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C# 8.0 のnull許容参照型を有効化
[opentween/open-tween.git] / OpenTween / Tween.cs
index 5e66ed2..c7efd06 100644 (file)
@@ -24,6 +24,8 @@
 // the Free Software Foundation, Inc., 51 Franklin Street - Fifth Floor,
 // Boston, MA 02110-1301, USA.
 
+#nullable enable
+
 //コンパイル後コマンド
 //"c:\Program Files\Microsoft.NET\SDK\v2.0\Bin\sgen.exe" /f /a:"$(TargetPath)"
 //"C:\Program Files\Microsoft Visual Studio 8\SDK\v2.0\Bin\sgen.exe" /f /a:"$(TargetPath)"
@@ -33,6 +35,7 @@ using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.ComponentModel;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Drawing;
 using System.Globalization;
 using System.IO;
@@ -60,23 +63,46 @@ namespace OpenTween
     public partial class TweenMain : OTBaseForm
     {
         //各種設定
-        private Size _mySize;           //画面サイズ
-        private Point _myLoc;           //画面位置
-        private int _mySpDis;           //区切り位置
-        private int _mySpDis2;          //発言欄区切り位置
-        private int _mySpDis3;          //プレビュー区切り位置
-        private int _iconSz;            //アイコンサイズ(現在は16、24、48の3種類。将来直接数字指定可能とする 注:24x24の場合に26と指定しているのはMSゴシック系フォントのための仕様)
-        private bool _iconCol;          //1列表示の時true(48サイズのとき)
+
+        /// <summary>画面サイズ</summary>
+        private Size _mySize;
+
+        /// <summary>画面位置</summary>
+        private Point _myLoc;
+
+        /// <summary>区切り位置</summary>
+        private int _mySpDis;
+
+        /// <summary>発言欄区切り位置</summary>
+        private int _mySpDis2;
+
+        /// <summary>プレビュー区切り位置</summary>
+        private int _mySpDis3;
+
+        /// <summary>アイコンサイズ</summary>
+        /// <remarks>
+        /// 現在は16、24、48の3種類。将来直接数字指定可能とする
+        /// 注:24x24の場合に26と指定しているのはMSゴシック系フォントのための仕様
+        /// </remarks>
+        private int _iconSz;
+
+        private bool _iconCol; // 1列表示の時true(48サイズのとき)
 
         //雑多なフラグ類
-        private bool _initial;         //true:起動時処理中
+        private bool _initial; // true:起動時処理中
         private bool _initialLayout = true;
-        private bool _ignoreConfigSave;         //true:起動時処理中
-        private bool _tabDrag;           //タブドラッグ中フラグ(DoDragDropを実行するかの判定用)
-        private TabPage _beforeSelectedTab; //タブが削除されたときに前回選択されていたときのタブを選択する為に保持
+        private bool _ignoreConfigSave; // true:起動時処理中
+
+        /// <summary>タブドラッグ中フラグ(DoDragDropを実行するかの判定用)</summary>
+        private bool _tabDrag;
+
+        private TabPage? _beforeSelectedTab; // タブが削除されたときに前回選択されていたときのタブを選択する為に保持
         private Point _tabMouseDownPoint;
-        private string _rclickTabName;      //右クリックしたタブの名前(Tabコントロール機能不足対応)
-        private readonly object _syncObject = new object();    //ロック用
+
+        /// <summary>右クリックしたタブの名前(Tabコントロール機能不足対応)</summary>
+        private string? _rclickTabName;
+
+        private readonly object _syncObject = new object(); // ロック用
 
         private const string detailHtmlFormatHeaderMono = 
             "<html><head><meta http-equiv=\"X-UA-Compatible\" content=\"IE=8\">"
@@ -104,8 +130,8 @@ namespace OpenTween
             + "--></style>"
             + "</head><body><p>";
         private const string detailHtmlFormatFooterColor = "</p></body></html>";
-        private string detailHtmlFormatHeader;
-        private string detailHtmlFormatFooter;
+        private string detailHtmlFormatHeader = null!;
+        private string detailHtmlFormatFooter = null!;
 
         private bool _myStatusError = false;
         private bool _myStatusOnline = false;
@@ -113,82 +139,157 @@ namespace OpenTween
         private FormWindowState _formWindowState = FormWindowState.Normal; // フォームの状態保存用 通知領域からアイコンをクリックして復帰した際に使用する
 
         //twitter解析部
-        private TwitterApi twitterApi = new TwitterApi();
-        private Twitter tw;
+        private readonly TwitterApi twitterApi = new TwitterApi();
+        private Twitter tw = null!;
 
         //Growl呼び出し部
-        private GrowlHelper gh = new GrowlHelper(ApplicationSettings.ApplicationName);
+        private readonly GrowlHelper gh = new GrowlHelper(ApplicationSettings.ApplicationName);
 
         //サブ画面インスタンス
-        internal SearchWordDialog SearchDialog = new SearchWordDialog();     //検索画面インスタンス
-        private OpenURL UrlDialog = new OpenURL();
-        public AtIdSupplement AtIdSupl;     //@id補助
-        public AtIdSupplement HashSupl;    //Hashtag補助
-        public HashtagManage HashMgr;
-        private EventViewerDialog evtDialog;
+
+        /// <summary>検索画面インスタンス</summary>
+        internal SearchWordDialog SearchDialog = new SearchWordDialog();
+
+        private readonly OpenURL UrlDialog = new OpenURL();
+
+        /// <summary>@id補助</summary>
+        public AtIdSupplement AtIdSupl = null!;
+
+        /// <summary>Hashtag補助</summary>
+        public AtIdSupplement HashSupl = null!;
+
+        public HashtagManage HashMgr = null!;
+        private EventViewerDialog evtDialog = null!;
 
         //表示フォント、色、アイコン
-        private Font _fntUnread;            //未読用フォント
-        private Color _clUnread;            //未読用文字色
-        private Font _fntReaded;            //既読用フォント
-        private Color _clReaded;            //既読用文字色
-        private Color _clFav;               //Fav用文字色
-        private Color _clOWL;               //片思い用文字色
-        private Color _clRetweet;               //Retweet用文字色
-        private Color _clHighLight = Color.FromKnownColor(KnownColor.HighlightText);         //選択中の行用文字色
-        private Font _fntDetail;            //発言詳細部用フォント
-        private Color _clDetail;              //発言詳細部用色
-        private Color _clDetailLink;          //発言詳細部用リンク文字色
-        private Color _clDetailBackcolor;     //発言詳細部用背景色
-        private Color _clSelf;              //自分の発言用背景色
-        private Color _clAtSelf;            //自分宛返信用背景色
-        private Color _clTarget;            //選択発言者の他の発言用背景色
-        private Color _clAtTarget;          //選択発言中の返信先用背景色
-        private Color _clAtFromTarget;      //選択発言者への返信発言用背景色
-        private Color _clAtTo;              //選択発言の唯一@先
-        private Color _clListBackcolor;       //リスト部通常発言背景色
-        private Color _clInputBackcolor;      //入力欄背景色
-        private Color _clInputFont;           //入力欄文字色
-        private Font _fntInputFont;           //入力欄フォント
-        private ImageCache IconCache;        //アイコン画像リスト
-        private Icon NIconAt;               //At.ico             タスクトレイアイコン:通常時
-        private Icon NIconAtRed;            //AtRed.ico          タスクトレイアイコン:通信エラー時
-        private Icon NIconAtSmoke;          //AtSmoke.ico        タスクトレイアイコン:オフライン時
-        private Icon[] NIconRefresh = new Icon[4];       //Refresh.ico        タスクトレイアイコン:更新中(アニメーション用に4種類を保持するリスト)
-        private Icon TabIcon;               //Tab.ico            未読のあるタブ用アイコン
-        private Icon MainIcon;              //Main.ico           画面左上のアイコン
-        private Icon ReplyIcon;               //5g
-        private Icon ReplyIconBlink;          //6g
-
-        private ImageList _listViewImageList = new ImageList();    //ListViewItemの高さ変更用
-
-        private PostClass _anchorPost;
+
+        /// <summary>未読用フォント</summary>
+        private Font _fntUnread = null!;
+
+        /// <summary>未読用文字色</summary>
+        private Color _clUnread;
+
+        /// <summary>既読用フォント</summary>
+        private Font _fntReaded = null!;
+
+        /// <summary>既読用文字色</summary>
+        private Color _clReaded;
+
+        /// <summary>Fav用文字色</summary>
+        private Color _clFav;
+
+        /// <summary>片思い用文字色</summary>
+        private Color _clOWL;
+
+        /// <summary>Retweet用文字色</summary>
+        private Color _clRetweet;
+
+        /// <summary>選択中の行用文字色</summary>
+        private readonly Color _clHighLight = Color.FromKnownColor(KnownColor.HighlightText);
+
+        /// <summary>発言詳細部用フォント</summary>
+        private Font _fntDetail = null!;
+
+        /// <summary>発言詳細部用色</summary>
+        private Color _clDetail;
+
+        /// <summary>発言詳細部用リンク文字色</summary>
+        private Color _clDetailLink;
+
+        /// <summary>発言詳細部用背景色</summary>
+        private Color _clDetailBackcolor;
+
+        /// <summary>自分の発言用背景色</summary>
+        private Color _clSelf;
+
+        /// <summary>自分宛返信用背景色</summary>
+        private Color _clAtSelf;
+
+        /// <summary>選択発言者の他の発言用背景色</summary>
+        private Color _clTarget;
+
+        /// <summary>選択発言中の返信先用背景色</summary>
+        private Color _clAtTarget;
+
+        /// <summary>選択発言者への返信発言用背景色</summary>
+        private Color _clAtFromTarget;
+
+        /// <summary>選択発言の唯一@先</summary>
+        private Color _clAtTo;
+
+        /// <summary>リスト部通常発言背景色</summary>
+        private Color _clListBackcolor;
+
+        /// <summary>入力欄背景色</summary>
+        private Color _clInputBackcolor;
+
+        /// <summary>入力欄文字色</summary>
+        private Color _clInputFont;
+
+        /// <summary>入力欄フォント</summary>
+        private Font _fntInputFont = null!;
+
+        /// <summary>アイコン画像リスト</summary>
+        private ImageCache IconCache = null!;
+
+        /// <summary>タスクトレイアイコン:通常時 (At.ico)</summary>
+        private Icon NIconAt = null!;
+
+        /// <summary>タスクトレイアイコン:通信エラー時 (AtRed.ico)</summary>
+        private Icon NIconAtRed = null!;
+
+        /// <summary>タスクトレイアイコン:オフライン時 (AtSmoke.ico)</summary>
+        private Icon NIconAtSmoke = null!;
+
+        /// <summary>タスクトレイアイコン:更新中 (Refresh.ico)</summary>
+        private Icon[] NIconRefresh = new Icon[4];
+
+        /// <summary>未読のあるタブ用アイコン (Tab.ico)</summary>
+        private Icon TabIcon = null!;
+
+        /// <summary>画面左上のアイコン (Main.ico)</summary>
+        private Icon MainIcon = null!;
+
+        private Icon ReplyIcon = null!;
+        private Icon ReplyIconBlink = null!;
+
+        private readonly ImageList _listViewImageList = new ImageList();    //ListViewItemの高さ変更用
+
+        private PostClass? _anchorPost;
         private bool _anchorFlag;        //true:関連発言移動中(関連移動以外のオペレーションをするとfalseへ。trueだとリスト背景色をアンカー発言選択中として描画)
 
-        private List<StatusTextHistory> _history = new List<StatusTextHistory>();   //発言履歴
-        private int _hisIdx;                  //発言履歴カレントインデックス
+        /// <summary>発言履歴</summary>
+        private readonly List<StatusTextHistory> _history = new List<StatusTextHistory>();
+
+        /// <summary>発言履歴カレントインデックス</summary>
+        private int _hisIdx;
 
         //発言投稿時のAPI引数(発言編集時に設定。手書きreplyでは設定されない)
-        private (long StatusId, string ScreenName)? inReplyTo = null; // リプライ先のステータスID・スクリーン名
+
+        /// <summary>リプライ先のステータスID・スクリーン名</summary>
+        private (long StatusId, string ScreenName)? inReplyTo = null;
 
         //時速表示用
-        private List<DateTimeUtc> _postTimestamps = new List<DateTimeUtc>();
-        private List<DateTimeUtc> _favTimestamps = new List<DateTimeUtc>();
+        private readonly List<DateTimeUtc> _postTimestamps = new List<DateTimeUtc>();
+        private readonly List<DateTimeUtc> _favTimestamps = new List<DateTimeUtc>();
 
         // 以下DrawItem関連
-        private SolidBrush _brsHighLight = new SolidBrush(Color.FromKnownColor(KnownColor.Highlight));
-        private SolidBrush _brsBackColorMine;
-        private SolidBrush _brsBackColorAt;
-        private SolidBrush _brsBackColorYou;
-        private SolidBrush _brsBackColorAtYou;
-        private SolidBrush _brsBackColorAtFromTarget;
-        private SolidBrush _brsBackColorAtTo;
-        private SolidBrush _brsBackColorNone;
-        private SolidBrush _brsDeactiveSelection = new SolidBrush(Color.FromKnownColor(KnownColor.ButtonFace)); //Listにフォーカスないときの選択行の背景色
-        private StringFormat sfTab = new StringFormat();
+        private readonly SolidBrush _brsHighLight = new SolidBrush(Color.FromKnownColor(KnownColor.Highlight));
+        private SolidBrush _brsBackColorMine = null!;
+        private SolidBrush _brsBackColorAt = null!;
+        private SolidBrush _brsBackColorYou = null!;
+        private SolidBrush _brsBackColorAtYou = null!;
+        private SolidBrush _brsBackColorAtFromTarget = null!;
+        private SolidBrush _brsBackColorAtTo = null!;
+        private SolidBrush _brsBackColorNone = null!;
+
+        /// <summary>Listにフォーカスないときの選択行の背景色</summary>
+        private readonly SolidBrush _brsDeactiveSelection = new SolidBrush(Color.FromKnownColor(KnownColor.ButtonFace));
+
+        private readonly StringFormat sfTab = new StringFormat();
 
         //////////////////////////////////////////////////////////////////////////////////////////////////////////
-        private TabInformations _statuses;
+        private TabInformations _statuses = null!;
 
         /// <summary>
         /// 現在表示している発言一覧の <see cref="ListView"/> に対するキャッシュ
@@ -198,12 +299,12 @@ namespace OpenTween
         /// 使用する場合には <see cref="_listItemCache"/> に対して直接メソッド等を呼び出さずに
         /// 一旦ローカル変数に代入してから参照すること。
         /// </remarks>
-        private ListViewItemCache _listItemCache = null;
+        private ListViewItemCache? _listItemCache = null;
 
         internal class ListViewItemCache
         {
             /// <summary>アイテムをキャッシュする対象の <see cref="ListView"/></summary>
-            public ListView TargetList { get; set; }
+            public ListView TargetList { get; set; } = null!;
 
             /// <summary>キャッシュする範囲の開始インデックス</summary>
             public int StartIndex { get; set; }
@@ -212,7 +313,7 @@ namespace OpenTween
             public int EndIndex { get; set; }
 
             /// <summary>キャッシュされた範囲に対応する <see cref="ListViewItem"/> と <see cref="PostClass"/> の組</summary>
-            public (ListViewItem, PostClass)[] Cache { get; set; }
+            public (ListViewItem, PostClass)[] Cache { get; set; } = null!;
 
             /// <summary>キャッシュされたアイテムの件数</summary>
             public int Count
@@ -230,7 +331,7 @@ namespace OpenTween
 
             /// <summary>指定されたインデックスの <see cref="ListViewItem"/> と <see cref="PostClass"/> をキャッシュから取得することを試みます</summary>
             /// <returns>取得に成功すれば true、それ以外は false</returns>
-            public bool TryGetValue(int index, out ListViewItem item, out PostClass post)
+            public bool TryGetValue(int index, [NotNullWhen(true)] out ListViewItem? item, [NotNullWhen(true)] out PostClass? post)
             {
                 if (this.Contains(index))
                 {
@@ -249,38 +350,38 @@ namespace OpenTween
         private bool _isColumnChanged = false;
 
         private const int MAX_WORKER_THREADS = 20;
-        private SemaphoreSlim workerSemaphore = new SemaphoreSlim(MAX_WORKER_THREADS);
-        private CancellationTokenSource workerCts = new CancellationTokenSource();
-        private IProgress<string> workerProgress;
+        private readonly SemaphoreSlim workerSemaphore = new SemaphoreSlim(MAX_WORKER_THREADS);
+        private readonly CancellationTokenSource workerCts = new CancellationTokenSource();
+        private readonly IProgress<string> workerProgress = null!;
 
         private int UnreadCounter = -1;
         private int UnreadAtCounter = -1;
 
-        private string[] ColumnOrgText = new string[9];
-        private string[] ColumnText = new string[9];
+        private readonly string[] ColumnOrgText = new string[9];
+        private readonly string[] ColumnText = new string[9];
 
         private bool _DoFavRetweetFlags = false;
 
         //////////////////////////////////////////////////////////////////////////////////////////////////////////
 
         private readonly TimelineScheduler timelineScheduler = new TimelineScheduler();
-        private ThrottlingTimer RefreshThrottlingTimer;
-        private ThrottlingTimer colorizeDebouncer;
-        private ThrottlingTimer selectionDebouncer;
-        private ThrottlingTimer saveConfigDebouncer;
+        private ThrottlingTimer RefreshThrottlingTimer = null!;
+        private ThrottlingTimer colorizeDebouncer = null!;
+        private ThrottlingTimer selectionDebouncer = null!;
+        private ThrottlingTimer saveConfigDebouncer = null!;
 
-        private string recommendedStatusFooter;
+        private string recommendedStatusFooter = null!;
         private bool urlMultibyteSplit = false;
         private bool preventSmsCommand = true;
 
-        //URL短縮のUndo用
+        // URL短縮のUndo用
         private struct urlUndo
         {
             public string Before;
             public string After;
         }
 
-        private List<urlUndo> urlUndoBuffer = null;
+        private List<urlUndo>? urlUndoBuffer = null;
 
         private readonly struct ReplyChain
         {
@@ -296,8 +397,11 @@ namespace OpenTween
             }
         }
 
-        private Stack<ReplyChain> replyChains; //[, ]でのリプライ移動の履歴
-        private Stack<(TabModel, PostClass)> selectPostChains = new Stack<(TabModel, PostClass)>(); //ポスト選択履歴
+        /// <summary>[, ]でのリプライ移動の履歴</summary>
+        private Stack<ReplyChain>? replyChains;
+
+        /// <summary>ポスト選択履歴</summary>
+        private readonly Stack<(TabModel, PostClass?)> selectPostChains = new Stack<(TabModel, PostClass?)>();
 
         public TabModel CurrentTab
             => this._statuses.SelectedTab;
@@ -311,10 +415,10 @@ namespace OpenTween
         public DetailsListView CurrentListView
             => (DetailsListView)this.CurrentTabPage.Tag;
 
-        public PostClass CurrentPost
+        public PostClass? CurrentPost
             => this.CurrentTab.SelectedPost;
 
-        //検索処理タイプ
+        /// <summary>検索処理タイプ</summary>
         internal enum SEARCHTYPE
         {
             DialogSearch,
@@ -326,8 +430,11 @@ namespace OpenTween
         {
             public string status = "";
             public (long StatusId, string ScreenName)? inReplyTo = null;
-            public string imageService = "";      //画像投稿サービス名
-            public IMediaItem[] mediaItems = null;
+
+            /// <summary>画像投稿サービス名</summary>
+            public string imageService = "";
+
+            public IMediaItem[]? mediaItems = null;
             public StatusTextHistory()
             {
             }
@@ -488,7 +595,7 @@ namespace OpenTween
             }
         }
 
-        private Icon LoadIcon(string filePath)
+        private Icon? LoadIcon(string filePath)
         {
             if (!File.Exists(filePath))
                 return null;
@@ -507,7 +614,7 @@ namespace OpenTween
         {
             this.InitColumnText();
 
-            ColumnHeader[] columns = null;
+            ColumnHeader[]? columns = null;
             try
             {
                 if (this._iconCol)
@@ -629,7 +736,7 @@ namespace OpenTween
             ColumnOrgText[6] = "";
             ColumnOrgText[7] = "Source";
 
-            int c = 0;
+            var c = 0;
             switch (_statuses.SortMode)
             {
                 case ComparerMode.Nickname:  //ニックネーム
@@ -786,8 +893,8 @@ namespace OpenTween
 
             Networking.Initialize();
 
-            bool saveRequired = false;
-            bool firstRun = false;
+            var saveRequired = false;
+            var firstRun = false;
 
             //ユーザー名、パスワードが未設定なら設定画面を表示(初回起動時など)
             if (string.IsNullOrEmpty(tw.Username))
@@ -816,7 +923,7 @@ namespace OpenTween
             tw.RestrictFavCheck = SettingManager.Common.RestrictFavCheck;
             tw.ReadOwnPost = SettingManager.Common.ReadOwnPost;
             tw.TrackWord = SettingManager.Common.TrackWord;
-            TrackToolStripMenuItem.Checked = !String.IsNullOrEmpty(tw.TrackWord);
+            TrackToolStripMenuItem.Checked = !string.IsNullOrEmpty(tw.TrackWord);
             tw.AllAtReply = SettingManager.Common.AllAtReply;
             AllrepliesToolStripMenuItem.Checked = tw.AllAtReply;
             ShortUrl.Instance.DisableExpanding = !SettingManager.Common.TinyUrlResolve;
@@ -934,11 +1041,11 @@ namespace OpenTween
             //タイトルバー領域
             if (this.WindowState != FormWindowState.Minimized)
             {
-                Rectangle tbarRect = new Rectangle(this._myLoc, new Size(_mySize.Width, SystemInformation.CaptionHeight));
-                bool outOfScreen = true;
+                var tbarRect = new Rectangle(this._myLoc, new Size(_mySize.Width, SystemInformation.CaptionHeight));
+                var outOfScreen = true;
                 if (Screen.AllScreens.Length == 1)    //ハングするとの報告
                 {
-                    foreach (Screen scr in Screen.AllScreens)
+                    foreach (var scr in Screen.AllScreens)
                     {
                         if (!Rectangle.Intersect(tbarRect, scr.Bounds).IsEmpty)
                         {
@@ -1082,7 +1189,7 @@ namespace OpenTween
             if (SettingManager.Common.HotkeyEnabled)
             {
                 //////グローバルホットキーの登録
-                HookGlobalHotkey.ModKeys modKey = HookGlobalHotkey.ModKeys.None;
+                var modKey = HookGlobalHotkey.ModKeys.None;
                 if ((SettingManager.Common.HotkeyModifier & Keys.Alt) == Keys.Alt)
                     modKey |= HookGlobalHotkey.ModKeys.Alt;
                 if ((SettingManager.Common.HotkeyModifier & Keys.Control) == Keys.Control)
@@ -1137,7 +1244,7 @@ namespace OpenTween
             TimerRefreshIcon.Enabled = false;
 
             _ignoreConfigSave = false;
-            this.TweenMain_Resize(null, null);
+            this.TweenMain_Resize(this, EventArgs.Empty);
             if (saveRequired) SaveConfigsAll(false);
 
             foreach (var ua in SettingManager.Common.UserAccounts)
@@ -1240,7 +1347,7 @@ namespace OpenTween
                         tab = new FilterTabModel(tabSetting.TabName);
                         break;
                     case MyCommon.TabUsageType.UserTimeline:
-                        tab = new UserTimelineTabModel(tabSetting.TabName, tabSetting.User);
+                        tab = new UserTimelineTabModel(tabSetting.TabName, tabSetting.User!);
                         break;
                     case MyCommon.TabUsageType.PublicSearch:
                         tab = new PublicSearchTabModel(tabSetting.TabName)
@@ -1250,7 +1357,7 @@ namespace OpenTween
                         };
                         break;
                     case MyCommon.TabUsageType.Lists:
-                        tab = new ListTimelineTabModel(tabSetting.TabName, tabSetting.ListInfo);
+                        tab = new ListTimelineTabModel(tabSetting.TabName, tabSetting.ListInfo!);
                         break;
                     case MyCommon.TabUsageType.Mute:
                         tab = new MuteTabModel(tabSetting.TabName);
@@ -1500,7 +1607,7 @@ namespace OpenTween
 
         internal struct ListViewSelection
         {
-            public long[] SelectedStatusIds { get; set; }
+            public long[]? SelectedStatusIds { get; set; }
             public long? SelectionMarkStatusId { get; set; }
             public long? FocusedStatusId { get; set; }
         }
@@ -1602,7 +1709,7 @@ namespace OpenTween
         private void RestoreListViewSelection(DetailsListView listView, TabModel tab, ListViewSelection listSelection)
         {
             // status_id から ListView 上のインデックスに変換
-            int[] selectedIndices = null;
+            int[]? selectedIndices = null;
             if (listSelection.SelectedStatusIds != null)
                 selectedIndices = tab.IndexOf(listSelection.SelectedStatusIds).Where(x => x != -1).ToArray();
 
@@ -1688,11 +1795,11 @@ namespace OpenTween
                     //Growlは一個ずつばらして通知。ただし、3ポスト以上あるときはまとめる
                     if (SettingManager.Common.IsUseNotifyGrowl)
                     {
-                        StringBuilder sb = new StringBuilder();
-                        bool reply = false;
-                        bool dm = false;
+                        var sb = new StringBuilder();
+                        var reply = false;
+                        var dm = false;
 
-                        foreach (PostClass post in notifyPosts)
+                        foreach (var post in notifyPosts)
                         {
                             if (!(notifyPosts.Length > 3))
                             {
@@ -1718,7 +1825,7 @@ namespace OpenTween
                                 if (notifyPosts.Last() != post) continue;
                             }
 
-                            StringBuilder title = new StringBuilder();
+                            var title = new StringBuilder();
                             GrowlHelper.NotifyType nt;
                             if (SettingManager.Common.DispUsername)
                             {
@@ -1756,7 +1863,7 @@ namespace OpenTween
                                 title.AppendFormat(Properties.Resources.RefreshTimeline_NotifyText, addCount);
                                 nt = GrowlHelper.NotifyType.Notify;
                             }
-                            string bText = sb.ToString();
+                            var bText = sb.ToString();
                             if (string.IsNullOrEmpty(bText)) return;
 
                             var image = this.IconCache.TryGetFromCache(post.ImageUrl);
@@ -1765,10 +1872,10 @@ namespace OpenTween
                     }
                     else
                     {
-                        StringBuilder sb = new StringBuilder();
-                        bool reply = false;
-                        bool dm = false;
-                        foreach (PostClass post in notifyPosts)
+                        var sb = new StringBuilder();
+                        var reply = false;
+                        var dm = false;
+                        foreach (var post in notifyPosts)
                         {
                             if (post.IsReply && !post.IsExcludeReply) reply = true;
                             if (post.IsDm) dm = true;
@@ -1786,7 +1893,7 @@ namespace OpenTween
 
                         }
                         //if (SettingDialog.DispUsername) { NotifyIcon1.BalloonTipTitle = tw.Username + " - "; } else { NotifyIcon1.BalloonTipTitle = ""; }
-                        StringBuilder title = new StringBuilder();
+                        var title = new StringBuilder();
                         ToolTipIcon ntIcon;
                         if (SettingManager.Common.DispUsername)
                         {
@@ -1824,7 +1931,7 @@ namespace OpenTween
                             title.Append(" ");
                             title.AppendFormat(Properties.Resources.RefreshTimeline_NotifyText, addCount);
                         }
-                        string bText = sb.ToString();
+                        var bText = sb.ToString();
                         if (string.IsNullOrEmpty(bText)) return;
                         //NotifyIcon1.BalloonTipText = sb.ToString();
                         //NotifyIcon1.ShowBalloonTip(500);
@@ -1841,15 +1948,13 @@ namespace OpenTween
             {
                 try
                 {
-                    string dir = Application.StartupPath;
+                    var dir = Application.StartupPath;
                     if (Directory.Exists(Path.Combine(dir, "Sounds")))
                     {
                         dir = Path.Combine(dir, "Sounds");
                     }
-                    using (SoundPlayer player = new SoundPlayer(Path.Combine(dir, soundFile)))
-                    {
-                        player.Play();
-                    }
+                    using var player = new SoundPlayer(Path.Combine(dir, soundFile));
+                    player.Play();
                 }
                 catch (Exception)
                 {
@@ -1859,7 +1964,7 @@ namespace OpenTween
             //mentions新着時に画面ブリンク
             if (!_initial && SettingManager.Common.BlinkNewMentions && newMentions && Form.ActiveForm == null)
             {
-                NativeMethods.FlashMyWindow(this.Handle, NativeMethods.FlashSpecification.FlashTray, 3);
+                NativeMethods.FlashMyWindow(this.Handle, 3);
             }
         }
 
@@ -1880,7 +1985,7 @@ namespace OpenTween
 
             this.PushSelectPostChain();
 
-            var post = this.CurrentPost;
+            var post = this.CurrentPost!;
             this._statuses.SetReadAllTab(post.StatusId, read: true);
 
             //キャッシュの書き換え
@@ -1909,7 +2014,7 @@ namespace OpenTween
             ChangeItemStyleRead(Read, itm, post, (DetailsListView)listCache.TargetList);
         }
 
-        private void ChangeItemStyleRead(bool Read, ListViewItem Item, PostClass Post, DetailsListView DList)
+        private void ChangeItemStyleRead(bool Read, ListViewItem Item, PostClass Post, DetailsListView? DList)
         {
             Font fnt;
             string star;
@@ -1961,7 +2066,7 @@ namespace OpenTween
         {
             //Index:更新対象のListviewItem.Index。Colorを返す。
             //-1は全キャッシュ。Colorは返さない(ダミーを戻す)
-            PostClass _post;
+            PostClass? _post;
             if (_anchorFlag)
                 _post = _anchorPost;
             else
@@ -1985,11 +2090,11 @@ namespace OpenTween
             }
         }
 
-        private void ColorizeList(ListViewItem Item, PostClass post, int Index)
+        private void ColorizeList(ListViewItem Item, PostClass post)
         {
             //Index:更新対象のListviewItem.Index。Colorを返す。
             //-1は全キャッシュ。Colorは返さない(ダミーを戻す)
-            PostClass _post;
+            PostClass? _post;
             if (_anchorFlag)
                 _post = _anchorPost;
             else
@@ -2073,9 +2178,9 @@ namespace OpenTween
             }
 
             var currentPost = this.CurrentPost;
-            if (this.ExistCurrentPost && StatusText.Text.Trim() == string.Format("RT @{0}: {1}", currentPost.ScreenName, currentPost.TextFromApi))
+            if (this.ExistCurrentPost && currentPost != null && StatusText.Text.Trim() == string.Format("RT @{0}: {1}", currentPost.ScreenName, currentPost.TextFromApi))
             {
-                DialogResult rtResult = MessageBox.Show(string.Format(Properties.Resources.PostButton_Click1, Environment.NewLine),
+                var rtResult = MessageBox.Show(string.Format(Properties.Resources.PostButton_Click1, Environment.NewLine),
                                                                "Retweet",
                                                                MessageBoxButtons.YesNoCancel,
                                                                MessageBoxIcon.Question);
@@ -2157,8 +2262,8 @@ namespace OpenTween
                     return;
             }
 
-            IMediaUploadService uploadService = null;
-            IMediaItem[] uploadItems = null;
+            IMediaUploadService? uploadService = null;
+            IMediaItem[]? uploadItems = null;
             if (ImageSelector.Visible)
             {
                 //画像投稿
@@ -2180,7 +2285,7 @@ namespace OpenTween
             //Google検索(試験実装)
             if (StatusText.Text.StartsWith("Google:", StringComparison.OrdinalIgnoreCase) && StatusText.Text.Trim().Length > 7)
             {
-                string tmp = string.Format(Properties.Resources.SearchItem2Url, Uri.EscapeDataString(StatusText.Text.Substring(7)));
+                var tmp = string.Format(Properties.Resources.SearchItem2Url, Uri.EscapeDataString(StatusText.Text.Substring(7)));
                 await this.OpenUriInBrowserAsync(tmp);
             }
 
@@ -2363,7 +2468,7 @@ namespace OpenTween
                             .ConfigureAwait(false);
                     }
                     catch (TwitterApiException ex)
-                        when (ex.ErrorResponse.Errors.All(x => x.Code == TwitterErrorCode.AlreadyFavorited))
+                        when (ex.Errors.All(x => x.Code == TwitterErrorCode.AlreadyFavorited))
                     {
                         // エラーコード 139 のみの場合は成功と見なす
                     }
@@ -2380,12 +2485,11 @@ namespace OpenTween
                     this._favTimestamps.Add(DateTimeUtc.Now);
 
                     // TLでも取得済みならfav反映
-                    if (this._statuses.ContainsKey(statusId))
+                    if (this._statuses.Posts.TryGetValue(statusId, out var postTl))
                     {
-                        var postTl = this._statuses[statusId];
                         postTl.IsFav = true;
 
-                        var favTab = this._statuses.GetTabByType(MyCommon.TabUsageType.Favorites);
+                        var favTab = this._statuses.FavoriteTab;
                         favTab.AddPostQueue(postTl);
                     }
 
@@ -2498,10 +2602,8 @@ namespace OpenTween
                     successIds.Add(statusId);
                     post.IsFav = false; // リスト再描画必要
 
-                    if (this._statuses.ContainsKey(statusId))
-                    {
-                        this._statuses[statusId].IsFav = false;
-                    }
+                    if (this._statuses.Posts.TryGetValue(statusId, out var tabinfoPost))
+                        tabinfoPost.IsFav = false;
 
                     // 検索,リスト,UserTimeline,Relatedの各タブに反映
                     foreach (var tb in this._statuses.GetTabsInnerStorageType())
@@ -2515,7 +2617,7 @@ namespace OpenTween
             if (ct.IsCancellationRequested)
                 return;
 
-            var favTab = this._statuses.GetTabByType(MyCommon.TabUsageType.Favorites);
+            var favTab = this._statuses.FavoriteTab;
             foreach (var statusId in successIds)
             {
                 // ツイートが削除された訳ではないので IsDeleted はセットしない
@@ -2552,7 +2654,7 @@ namespace OpenTween
             }
         }
 
-        private async Task PostMessageAsync(PostStatusParams postParams, IMediaUploadService uploadService, IMediaItem[] uploadItems)
+        private async Task PostMessageAsync(PostStatusParams postParams, IMediaUploadService? uploadService, IMediaItem[]? uploadItems)
         {
             await this.workerSemaphore.WaitAsync();
             this.RefreshTasktrayIcon();
@@ -2575,7 +2677,7 @@ namespace OpenTween
         }
 
         private async Task PostMessageAsyncInternal(IProgress<string> p, CancellationToken ct, PostStatusParams postParams,
-            IMediaUploadService uploadService, IMediaItem[] uploadItems)
+            IMediaUploadService? uploadService, IMediaItem[]? uploadItems)
         {
             if (ct.IsCancellationRequested)
                 return;
@@ -2585,7 +2687,7 @@ namespace OpenTween
 
             p.Report("Posting...");
 
-            PostClass post = null;
+            PostClass? post = null;
             var errMsg = "";
 
             try
@@ -2930,13 +3032,13 @@ namespace OpenTween
                     await ShowUserTimeline();
                     break;
                 case 4:
-                    ShowRelatedStatusesMenuItem_Click(null, null);
+                    ShowRelatedStatusesMenuItem_Click(this.ShowRelatedStatusesMenuItem, EventArgs.Empty);
                     break;
                 case 5:
-                    MoveToHomeToolStripMenuItem_Click(null, null);
+                    MoveToHomeToolStripMenuItem_Click(this.MoveToHomeToolStripMenuItem, EventArgs.Empty);
                     break;
                 case 6:
-                    StatusOpenMenuItem_Click(null, null);
+                    StatusOpenMenuItem_Click(this.StatusOpenMenuItem, EventArgs.Empty);
                     break;
                 case 7:
                     //動作なし
@@ -3020,7 +3122,7 @@ namespace OpenTween
             var listCache = this._listItemCache;
             if (listCache != null)
             {
-                if (listCache.TryGetValue(Index, out var item, out var post))
+                if (listCache.TryGetValue(Index, out _, out var post))
                     return post;
             }
 
@@ -3218,7 +3320,7 @@ namespace OpenTween
             }
             var tab = this.CurrentTab;
             var post = this.CurrentPost;
-            if (tab.TabType == MyCommon.TabUsageType.DirectMessage || !this.ExistCurrentPost || post.IsDm)
+            if (tab.TabType == MyCommon.TabUsageType.DirectMessage || !this.ExistCurrentPost || post == null || post.IsDm)
             {
                 FavAddToolStripMenuItem.Enabled = false;
                 FavRemoveToolStripMenuItem.Enabled = false;
@@ -3263,7 +3365,7 @@ namespace OpenTween
             //{
             //    RefreshMoreStripMenuItem.Enabled = false;
             //}
-            if (!this.ExistCurrentPost || post.InReplyToStatusId == null)
+            if (!this.ExistCurrentPost || post == null || post.InReplyToStatusId == null)
             {
                 RepliedStatusOpenMenuItem.Enabled = false;
             }
@@ -3271,7 +3373,7 @@ namespace OpenTween
             {
                 RepliedStatusOpenMenuItem.Enabled = true;
             }
-            if (!this.ExistCurrentPost || string.IsNullOrEmpty(post.RetweetedBy))
+            if (!this.ExistCurrentPost || post == null || string.IsNullOrEmpty(post.RetweetedBy))
             {
                 MoveToRTHomeMenuItem.Enabled = false;
             }
@@ -3280,7 +3382,7 @@ namespace OpenTween
                 MoveToRTHomeMenuItem.Enabled = true;
             }
 
-            if (this.ExistCurrentPost)
+            if (this.ExistCurrentPost && post != null)
             {
                 this.DeleteStripMenuItem.Enabled = post.CanDeleteBy(this.tw.UserId);
                 if (post.RetweetedByUserId == this.tw.UserId)
@@ -3319,7 +3421,7 @@ namespace OpenTween
 
             using (ControlTransaction.Cursor(this, Cursors.WaitCursor))
             {
-                Exception lastException = null;
+                Exception? lastException = null;
                 foreach (var post in posts)
                 {
                     if (!post.CanDeleteBy(this.tw.UserId))
@@ -3484,35 +3586,33 @@ namespace OpenTween
 
         private DialogResult ShowSettingDialog(bool showTaskbarIcon = false)
         {
-            DialogResult result = DialogResult.Abort;
+            var result = DialogResult.Abort;
 
-            using (var settingDialog = new AppendSettingDialog())
-            {
-                settingDialog.Icon = this.MainIcon;
-                settingDialog.Owner = this;
-                settingDialog.ShowInTaskbar = showTaskbarIcon;
-                settingDialog.IntervalChanged += this.TimerInterval_Changed;
+            using var settingDialog = new AppendSettingDialog();
+            settingDialog.Icon = this.MainIcon;
+            settingDialog.Owner = this;
+            settingDialog.ShowInTaskbar = showTaskbarIcon;
+            settingDialog.IntervalChanged += this.TimerInterval_Changed;
 
-                settingDialog.tw = this.tw;
-                settingDialog.twitterApi = this.twitterApi;
+            settingDialog.tw = this.tw;
+            settingDialog.twitterApi = this.twitterApi;
 
-                settingDialog.LoadConfig(SettingManager.Common, SettingManager.Local);
+            settingDialog.LoadConfig(SettingManager.Common, SettingManager.Local);
 
-                try
-                {
-                    result = settingDialog.ShowDialog(this);
-                }
-                catch (Exception)
-                {
-                    return DialogResult.Abort;
-                }
+            try
+            {
+                result = settingDialog.ShowDialog(this);
+            }
+            catch (Exception)
+            {
+                return DialogResult.Abort;
+            }
 
-                if (result == DialogResult.OK)
+            if (result == DialogResult.OK)
+            {
+                lock (_syncObject)
                 {
-                    lock (_syncObject)
-                    {
-                        settingDialog.SaveConfig(SettingManager.Common, SettingManager.Local);
-                    }
+                    settingDialog.SaveConfig(SettingManager.Common, SettingManager.Local);
                 }
             }
 
@@ -3696,7 +3796,7 @@ namespace OpenTween
 
                         foreach (TabPage tp in ListTab.TabPages)
                         {
-                            DetailsListView lst = (DetailsListView)tp.Tag;
+                            var lst = (DetailsListView)tp.Tag;
 
                             using (ControlTransaction.Update(lst))
                             {
@@ -3727,7 +3827,7 @@ namespace OpenTween
                     if (SettingManager.Common.HotkeyEnabled)
                     {
                         ///グローバルホットキーの登録。設定で変更可能にするかも
-                        HookGlobalHotkey.ModKeys modKey = HookGlobalHotkey.ModKeys.None;
+                        var modKey = HookGlobalHotkey.ModKeys.None;
                         if ((SettingManager.Common.HotkeyModifier & Keys.Alt) == Keys.Alt)
                             modKey |= HookGlobalHotkey.ModKeys.Alt;
                         if ((SettingManager.Common.HotkeyModifier & Keys.Control) == Keys.Control)
@@ -3743,7 +3843,7 @@ namespace OpenTween
                     if (SettingManager.Common.IsUseNotifyGrowl) gh.RegisterGrowl();
                     try
                     {
-                        StatusText_TextChanged(null, null);
+                        StatusText_TextChanged(this.StatusText, EventArgs.Empty);
                     }
                     catch (Exception)
                     {
@@ -3864,8 +3964,8 @@ namespace OpenTween
                 }
             }
             //ユニークなタブ名生成
-            string tabName = searchWord;
-            for (int i = 0; i <= 100; i++)
+            var tabName = searchWord;
+            for (var i = 0; i <= 100; i++)
             {
                 if (_statuses.ContainsTab(tabName))
                     tabName += "_";
@@ -3880,18 +3980,19 @@ namespace OpenTween
             ListTab.SelectedIndex = this._statuses.Tabs.Count - 1;
             //検索条件の設定
             var tabPage = this.CurrentTabPage;
-            ComboBox cmb = (ComboBox)tabPage.Controls["panelSearch"].Controls["comboSearch"];
+            var cmb = (ComboBox)tabPage.Controls["panelSearch"].Controls["comboSearch"];
             cmb.Items.Add(searchWord);
             cmb.Text = searchWord;
             SaveConfigsTabs();
             //検索実行
-            this.SearchButton_Click(tabPage.Controls["panelSearch"].Controls["comboSearch"], null);
+            this.SearchButton_Click(tabPage.Controls["panelSearch"].Controls["comboSearch"], EventArgs.Empty);
         }
 
         private async Task ShowUserTimeline()
         {
-            if (!this.ExistCurrentPost) return;
-            await this.AddNewTabForUserTimeline(this.CurrentPost.ScreenName);
+            var post = this.CurrentPost;
+            if (post == null || !this.ExistCurrentPost) return;
+            await this.AddNewTabForUserTimeline(post.ScreenName);
         }
 
         private void SearchComboBox_KeyDown(object sender, KeyEventArgs e)
@@ -3917,7 +4018,7 @@ namespace OpenTween
                 }
             }
             //ユニークなタブ名生成
-            string tabName = "user:" + user;
+            var tabName = "user:" + user;
             while (_statuses.ContainsTab(tabName))
             {
                 tabName += "_";
@@ -3945,7 +4046,7 @@ namespace OpenTween
             var _tabPage = new TabPage();
             var _listCustom = new DetailsListView();
 
-            int cnt = this._statuses.Tabs.Count;
+            var cnt = this._statuses.Tabs.Count;
 
             ///ToDo:Create and set controls follow tabtypes
 
@@ -3982,7 +4083,7 @@ namespace OpenTween
                         label.Text = userTab.ScreenName + "'s Timeline";
                     }
                     label.TextAlign = ContentAlignment.MiddleLeft;
-                    using (ComboBox tmpComboBox = new ComboBox())
+                    using (var tmpComboBox = new ComboBox())
                     {
                         label.Height = tmpComboBox.Height;
                     }
@@ -4140,11 +4241,12 @@ namespace OpenTween
         public bool RemoveSpecifiedTab(string TabName, bool confirm)
         {
             var tabInfo = _statuses.GetTabByName(TabName);
-            if (tabInfo.IsDefaultTabType || tabInfo.Protected) return false;
+            if (tabInfo == null || tabInfo.IsDefaultTabType || tabInfo.Protected)
+                return false;
 
             if (confirm)
             {
-                string tmp = string.Format(Properties.Resources.RemoveSpecifiedTabText1, Environment.NewLine);
+                var tmp = string.Format(Properties.Resources.RemoveSpecifiedTabText1, Environment.NewLine);
                 if (MessageBox.Show(tmp, TabName + " " + Properties.Resources.RemoveSpecifiedTabText2,
                                  MessageBoxButtons.OKCancel, MessageBoxIcon.Question, MessageBoxDefaultButton.Button2) == DialogResult.Cancel)
                 {
@@ -4161,7 +4263,7 @@ namespace OpenTween
             SetListProperty();   //他のタブに列幅等を反映
 
             //オブジェクトインスタンスの削除
-            DetailsListView _listCustom = (DetailsListView)_tabPage.Tag;
+            var _listCustom = (DetailsListView)_tabPage.Tag;
             _tabPage.Tag = null;
 
             using (ControlTransaction.Layout(this.SplitContainer1.Panel1, false))
@@ -4181,32 +4283,29 @@ namespace OpenTween
                 // 後付けのコントロールを破棄
                 if (tabInfo.TabType == MyCommon.TabUsageType.UserTimeline || tabInfo.TabType == MyCommon.TabUsageType.Lists)
                 {
-                    using (Control label = _tabPage.Controls["labelUser"])
-                    {
-                        _tabPage.Controls.Remove(label);
-                    }
+                    using var label = _tabPage.Controls["labelUser"];
+                    _tabPage.Controls.Remove(label);
                 }
                 else if (tabInfo.TabType == MyCommon.TabUsageType.PublicSearch)
                 {
-                    using (Control pnl = _tabPage.Controls["panelSearch"])
-                    {
-                        pnl.Enter -= SearchControls_Enter;
-                        pnl.Leave -= SearchControls_Leave;
-                        _tabPage.Controls.Remove(pnl);
+                    using var pnl = _tabPage.Controls["panelSearch"];
 
-                        foreach (Control ctrl in pnl.Controls)
+                    pnl.Enter -= SearchControls_Enter;
+                    pnl.Leave -= SearchControls_Leave;
+                    _tabPage.Controls.Remove(pnl);
+
+                    foreach (Control ctrl in pnl.Controls)
+                    {
+                        if (ctrl.Name == "buttonSearch")
                         {
-                            if (ctrl.Name == "buttonSearch")
-                            {
-                                ctrl.Click -= SearchButton_Click;
-                            }
-                            else if (ctrl.Name == "comboSearch")
-                            {
-                                ctrl.KeyDown -= SearchComboBox_KeyDown;
-                            }
-                            pnl.Controls.Remove(ctrl);
-                            ctrl.Dispose();
+                            ctrl.Click -= SearchButton_Click;
                         }
+                        else if (ctrl.Name == "comboSearch")
+                        {
+                            ctrl.KeyDown -= SearchComboBox_KeyDown;
+                        }
+                        pnl.Controls.Remove(ctrl);
+                        ctrl.Dispose();
                     }
                 }
 
@@ -4269,8 +4368,8 @@ namespace OpenTween
 
             if (!SettingManager.Common.TabMouseLock && e.Button == MouseButtons.Left && _tabDrag)
             {
-                string tn = "";
-                Rectangle dragEnableRectangle = new Rectangle(_tabMouseDownPoint.X - (SystemInformation.DragSize.Width / 2), _tabMouseDownPoint.Y - (SystemInformation.DragSize.Height / 2), SystemInformation.DragSize.Width, SystemInformation.DragSize.Height);
+                var tn = "";
+                var dragEnableRectangle = new Rectangle(_tabMouseDownPoint.X - (SystemInformation.DragSize.Width / 2), _tabMouseDownPoint.Y - (SystemInformation.DragSize.Height / 2), SystemInformation.DragSize.Width, SystemInformation.DragSize.Height);
                 if (!dragEnableRectangle.Contains(e.Location))
                 {
                     //タブが多段の場合にはMouseDownの前の段階で選択されたタブの段が変わっているので、このタイミングでカーソルの位置からタブを判定出来ない。
@@ -4291,7 +4390,7 @@ namespace OpenTween
                 _tabDrag = false;
             }
 
-            Point cpos = new Point(e.X, e.Y);
+            var cpos = new Point(e.X, e.Y);
             foreach (var (tab, index) in this._statuses.Tabs.WithIndex())
             {
                 var rect = ListTab.GetTabRect(index);
@@ -4322,10 +4421,10 @@ namespace OpenTween
 
             var currentListView = this.CurrentListView;
 
-            int[] dispOrder = new int[currentListView.Columns.Count];
-            for (int i = 0; i < currentListView.Columns.Count; i++)
+            var dispOrder = new int[currentListView.Columns.Count];
+            for (var i = 0; i < currentListView.Columns.Count; i++)
             {
-                for (int j = 0; j < currentListView.Columns.Count; j++)
+                for (var j = 0; j < currentListView.Columns.Count; j++)
                 {
                     if (currentListView.Columns[j].DisplayIndex == i)
                     {
@@ -4343,8 +4442,8 @@ namespace OpenTween
 
                 if (tb.Tag != null && tb.Controls.Count > 0)
                 {
-                    DetailsListView lst = (DetailsListView)tb.Tag;
-                    for (int i = 0; i < lst.Columns.Count; i++)
+                    var lst = (DetailsListView)tb.Tag;
+                    for (var i = 0; i < lst.Columns.Count; i++)
                     {
                         lst.Columns[dispOrder[i]].DisplayIndex = i;
                         lst.Columns[i].Width = currentListView.Columns[i].Width;
@@ -4361,7 +4460,7 @@ namespace OpenTween
             {
                 if (!SettingManager.Common.UseAtIdSupplement) return;
                 //@マーク
-                int cnt = AtIdSupl.ItemCount;
+                var cnt = AtIdSupl.ItemCount;
                 ShowSuplDialog(StatusText, AtIdSupl);
                 if (cnt != AtIdSupl.ItemCount)
                     this.MarkSettingAtIdModified();
@@ -4393,9 +4492,9 @@ namespace OpenTween
                 dialog.ShowDialog();
             }
             this.TopMost = SettingManager.Common.AlwaysTop;
-            int selStart = owner.SelectionStart;
-            string fHalf = "";
-            string eHalf = "";
+            var selStart = owner.SelectionStart;
+            var fHalf = "";
+            var eHalf = "";
             if (dialog.DialogResult == DialogResult.OK)
             {
                 if (!string.IsNullOrEmpty(dialog.inputText))
@@ -4438,8 +4537,8 @@ namespace OpenTween
             {
                 if (e.KeyCode == Keys.Space || e.KeyCode == Keys.ProcessKey)
                 {
-                    bool isSpace = false;
-                    foreach (char c in StatusText.Text)
+                    var isSpace = false;
+                    foreach (var c in StatusText.Text)
                     {
                         if (c == ' ' || c == ' ')
                         {
@@ -4455,17 +4554,17 @@ namespace OpenTween
                     {
                         e.Handled = true;
                         StatusText.Text = "";
-                        JumpUnreadMenuItem_Click(null, null);
+                        JumpUnreadMenuItem_Click(this.JumpUnreadMenuItem, EventArgs.Empty);
                     }
                 }
             }
-            this.StatusText_TextChanged(null, null);
+            this.StatusText_TextChanged(this.StatusText, EventArgs.Empty);
         }
 
         private void StatusText_TextChanged(object sender, EventArgs e)
         {
             //文字数カウント
-            int pLen = this.GetRestStatusCount(this.FormatStatusTextExtended(this.StatusText.Text));
+            var pLen = this.GetRestStatusCount(this.FormatStatusTextExtended(this.StatusText.Text));
             lblLen.Text = pLen.ToString();
             if (pLen < 0)
             {
@@ -4515,7 +4614,7 @@ namespace OpenTween
         /// </summary>
         private string RemoveAutoPopuratedMentions(string statusText, out long[] autoPopulatedUserIds)
         {
-            List<long> _autoPopulatedUserIds = new List<long>();
+            var _autoPopulatedUserIds = new List<long>();
 
             var replyToPost = this.inReplyTo != null ? this._statuses[this.inReplyTo.Value.StatusId] : null;
             if (replyToPost != null)
@@ -4544,7 +4643,7 @@ namespace OpenTween
         /// <summary>
         /// attachment_url に指定可能な URL が含まれていれば除去
         /// </summary>
-        private string RemoveAttachmentUrl(string statusText, out string attachmentUrl)
+        private string RemoveAttachmentUrl(string statusText, out string? attachmentUrl)
         {
             attachmentUrl = null;
 
@@ -4566,12 +4665,12 @@ namespace OpenTween
         }
 
         private string FormatStatusTextExtended(string statusText)
-            => this.FormatStatusTextExtended(statusText, out var autoPopulatedUserIds, out var attachmentUrl);
+            => this.FormatStatusTextExtended(statusText, out _, out _);
 
         /// <summary>
         /// <see cref="FormatStatusText"/> に加えて、拡張モードで140字にカウントされない文字列の除去を行います
         /// </summary>
-        private string FormatStatusTextExtended(string statusText, out long[] autoPopulatedUserIds, out string attachmentUrl)
+        private string FormatStatusTextExtended(string statusText, out long[] autoPopulatedUserIds, out string? attachmentUrl)
         {
             statusText = this.RemoveAutoPopuratedMentions(statusText, out autoPopulatedUserIds);
 
@@ -4691,7 +4790,7 @@ namespace OpenTween
             return remainCount;
         }
 
-        private IMediaUploadService GetSelectedImageService()
+        private IMediaUploadService? GetSelectedImageService()
             => this.ImageSelector.Visible ? this.ImageSelector.SelectedService : null;
 
         private void MyList_CacheVirtualItems(object sender, CacheVirtualItemsEventArgs e)
@@ -4716,7 +4815,7 @@ namespace OpenTween
             var listCache = this._listItemCache;
             if (listCache?.TargetList == sender)
             {
-                if (listCache.TryGetValue(e.ItemIndex, out var item, out var cacheItemPost))
+                if (listCache.TryGetValue(e.ItemIndex, out var item, out _))
                 {
                     e.Item = item;
                     return;
@@ -4728,7 +4827,7 @@ namespace OpenTween
             var tab = this._statuses.Tabs[tabPage.Text];
             try
             {
-                e.Item = this.CreateItem(tab, tab[e.ItemIndex], e.ItemIndex);
+                e.Item = this.CreateItem(tab, tab[e.ItemIndex]);
             }
             catch (Exception)
             {
@@ -4758,7 +4857,7 @@ namespace OpenTween
             var tab = this.CurrentTab;
             var posts = tabInfo[startIndex, endIndex]; //配列で取得
             var listItems = Enumerable.Range(0, cacheLength)
-                .Select(x => this.CreateItem(tab, posts[x], startIndex + x))
+                .Select(x => this.CreateItem(tab, posts[x]))
                 .ToArray();
 
             var listCache = new ListViewItemCache
@@ -4778,9 +4877,9 @@ namespace OpenTween
         private void PurgeListViewItemCache()
             => Interlocked.Exchange(ref this._listItemCache, null);
 
-        private ListViewItem CreateItem(TabModel tab, PostClass Post, int Index)
+        private ListViewItem CreateItem(TabModel tab, PostClass Post)
         {
-            StringBuilder mk = new StringBuilder();
+            var mk = new StringBuilder();
             //if (Post.IsDeleted) mk.Append("×");
             //if (Post.IsMark) mk.Append("♪");
             //if (Post.IsProtect) mk.Append("Ю");
@@ -4814,7 +4913,7 @@ namespace OpenTween
             itm.StateIndex = Post.StateIndex;
             itm.Tag = Post;
 
-            bool read = Post.IsRead;
+            var read = Post.IsRead;
             // 未読管理していなかったら既読として扱う
             if (!tab.UnreadManage || !SettingManager.Common.UnreadManage)
                 read = true;
@@ -4822,7 +4921,7 @@ namespace OpenTween
             ChangeItemStyleRead(read, itm, Post, null);
 
             if (tab.TabName == this.CurrentTabName)
-                this.ColorizeList(itm, Post, Index);
+                this.ColorizeList(itm, Post);
 
             return itm;
         }
@@ -4874,7 +4973,7 @@ namespace OpenTween
             if (e.State == 0) return;
             e.DrawDefault = false;
 
-            SolidBrush brs2 = null;
+            SolidBrush brs2;
             if (!e.Item.Selected)     //e.ItemStateでうまく判定できない???
             {
                 if (e.Item.BackColor == _clSelf)
@@ -4916,14 +5015,14 @@ namespace OpenTween
 
                 RectangleF rct = e.Bounds;
                 rct.Width = e.Header.Width;
-                int fontHeight = e.Item.Font.Height;
+                var fontHeight = e.Item.Font.Height;
                 if (_iconCol)
                 {
                     rct.Y += fontHeight;
                     rct.Height -= fontHeight;
                 }
 
-                int drawLineCount = Math.Max(1, Math.DivRem((int)rct.Height, fontHeight, out var heightDiff));
+                var drawLineCount = Math.Max(1, Math.DivRem((int)rct.Height, fontHeight, out var heightDiff));
 
                 //if (heightDiff > fontHeight * 0.7)
                 //{
@@ -4956,37 +5055,36 @@ namespace OpenTween
 
                 if (rct.Width > 0)
                 {
-                    Color color = (!e.Item.Selected) ? e.Item.ForeColor :   //選択されていない行
+                    var color = (!e.Item.Selected) ? e.Item.ForeColor :   //選択されていない行
                         (((Control)sender).Focused) ? _clHighLight :        //選択中の行
                         _clUnread;
 
                     if (_iconCol)
                     {
-                        Rectangle rctB = e.Bounds;
+                        var rctB = e.Bounds;
                         rctB.Width = e.Header.Width;
                         rctB.Height = fontHeight;
 
-                        using (Font fnt = new Font(e.Item.Font, FontStyle.Bold))
-                        {
-                            TextRenderer.DrawText(e.Graphics,
-                                                    post.IsDeleted ? "(DELETED)" : post.TextSingleLine,
-                                                    e.Item.Font,
-                                                    Rectangle.Round(rct),
-                                                    color,
-                                                    TextFormatFlags.WordBreak |
-                                                    TextFormatFlags.EndEllipsis |
-                                                    TextFormatFlags.GlyphOverhangPadding |
-                                                    TextFormatFlags.NoPrefix);
-                            TextRenderer.DrawText(e.Graphics,
-                                                    e.Item.SubItems[4].Text + " / " + e.Item.SubItems[1].Text + " (" + e.Item.SubItems[3].Text + ") " + e.Item.SubItems[5].Text + e.Item.SubItems[6].Text + " [" + e.Item.SubItems[7].Text + "]",
-                                                    fnt,
-                                                    rctB,
-                                                    color,
-                                                    TextFormatFlags.SingleLine |
-                                                    TextFormatFlags.EndEllipsis |
-                                                    TextFormatFlags.GlyphOverhangPadding |
-                                                    TextFormatFlags.NoPrefix);
-                        }
+                        using var fnt = new Font(e.Item.Font, FontStyle.Bold);
+
+                        TextRenderer.DrawText(e.Graphics,
+                            post.IsDeleted ? "(DELETED)" : post.TextSingleLine,
+                            e.Item.Font,
+                            Rectangle.Round(rct),
+                            color,
+                            TextFormatFlags.WordBreak |
+                            TextFormatFlags.EndEllipsis |
+                            TextFormatFlags.GlyphOverhangPadding |
+                            TextFormatFlags.NoPrefix);
+                        TextRenderer.DrawText(e.Graphics,
+                            e.Item.SubItems[4].Text + " / " + e.Item.SubItems[1].Text + " (" + e.Item.SubItems[3].Text + ") " + e.Item.SubItems[5].Text + e.Item.SubItems[6].Text + " [" + e.Item.SubItems[7].Text + "]",
+                            fnt,
+                            rctB,
+                            color,
+                            TextFormatFlags.SingleLine |
+                            TextFormatFlags.EndEllipsis |
+                            TextFormatFlags.GlyphOverhangPadding |
+                            TextFormatFlags.NoPrefix);
                     }
                     else
                     {
@@ -5031,10 +5129,10 @@ namespace OpenTween
         {
             if (_iconSz == 0) return;
 
-            ImageListViewItem item = (ImageListViewItem)e.Item;
+            var item = (ImageListViewItem)e.Item;
 
             //e.Bounds.Leftが常に0を指すから自前で計算
-            Rectangle itemRect = item.Bounds;
+            var itemRect = item.Bounds;
             var col0 = e.Item.ListView.Columns[0];
             itemRect.Width = col0.Width;
 
@@ -5082,7 +5180,7 @@ namespace OpenTween
 
             if (item.StateIndex > -1)
             {
-                Rectangle stateRect = Rectangle.Intersect(new Rectangle(new Point(iconRect.X + realIconSize.Width + 2, iconRect.Y), realStateSize), itemRect);
+                var stateRect = Rectangle.Intersect(new Rectangle(new Point(iconRect.X + realIconSize.Width + 2, iconRect.Y), realStateSize), itemRect);
                 if (stateRect.Width > 0)
                 {
                     //e.Graphics.FillRectangle(Brushes.White, stateRect);
@@ -5250,7 +5348,7 @@ namespace OpenTween
             }
             this.TopMost = SettingManager.Common.AlwaysTop;
 
-            var searchOptions = this.SearchDialog.ResultOptions;
+            var searchOptions = this.SearchDialog.ResultOptions!;
             if (searchOptions.Type == SearchWordDialog.SearchType.Timeline)
             {
                 if (searchOptions.NewTab)
@@ -5340,7 +5438,7 @@ namespace OpenTween
 
         private void AboutMenuItem_Click(object sender, EventArgs e)
         {
-            using (TweenAboutBox about = new TweenAboutBox())
+            using (var about = new TweenAboutBox())
             {
                 about.ShowDialog(this);
             }
@@ -5354,10 +5452,8 @@ namespace OpenTween
             if (ImageSelector.Enabled)
                 return;
 
-            TabModel foundTab = null;
-            int foundIndex = 0;
-
-            DetailsListView lst = null;
+            TabModel? foundTab = null;
+            var foundIndex = 0;
 
             //現在タブから最終タブまで探索
             foreach (var (tab, index) in this._statuses.Tabs.WithIndex().Skip(bgnIdx))
@@ -5368,7 +5464,6 @@ namespace OpenTween
                     ListTab.SelectedIndex = index;
                     foundTab = tab;
                     foundIndex = unreadIndex;
-                    lst = (DetailsListView)this.ListTab.TabPages[index].Tag;
                     break;
                 }
             }
@@ -5384,12 +5479,13 @@ namespace OpenTween
                         ListTab.SelectedIndex = index;
                         foundTab = tab;
                         foundIndex = unreadIndex;
-                        lst = (DetailsListView)this.ListTab.TabPages[index].Tag;
                         break;
                     }
                 }
             }
 
+            DetailsListView lst;
+
             if (foundTab == null)
             {
                 //全部調べたが未読見つからず→先頭タブの最新発言へ
@@ -5407,6 +5503,11 @@ namespace OpenTween
 
                 lst = (DetailsListView)tabPage.Tag;
             }
+            else
+            {
+                var foundTabIndex = this._statuses.Tabs.IndexOf(foundTab);
+                lst = (DetailsListView)this.ListTab.TabPages[foundTabIndex].Tag;
+            }
 
             SelectListItem(lst, foundIndex);
 
@@ -5463,9 +5564,12 @@ namespace OpenTween
 
         public class VersionInfo
         {
-            public Version Version { get; set; }
-            public Uri DownloadUri { get; set; }
-            public string ReleaseNote { get; set; }
+            public Version Version { get; }
+            public Uri DownloadUri { get; }
+            public string ReleaseNote { get; }
+
+            public VersionInfo(Version version, Uri downloadUri, string releaseNote)
+                => (this.Version, this.DownloadUri, this.ReleaseNote) = (version, downloadUri, releaseNote);
         }
 
         /// <summary>
@@ -5487,12 +5591,11 @@ namespace OpenTween
 
             msgBody = Regex.Replace(msgBody, "(?<!\r)\n", "\r\n"); // LF -> CRLF
 
-            return new VersionInfo
-            {
-                Version = Version.Parse(msgHeader[0]),
-                DownloadUri = new Uri(msgHeader[1]),
-                ReleaseNote = msgBody,
-            };
+            return new VersionInfo(
+                version: Version.Parse(msgHeader[0]),
+                downloadUri: new Uri(msgHeader[1]),
+                releaseNote: msgBody
+            );
         }
 
         private async Task CheckNewVersion(bool startup = false)
@@ -5523,21 +5626,20 @@ namespace OpenTween
                 if (startup && versionInfo.Version <= SettingManager.Common.SkipUpdateVersion)
                     return;
 
-                using (var dialog = new UpdateDialog())
-                {
-                    dialog.SummaryText = string.Format(Properties.Resources.CheckNewVersionText3,
-                        MyCommon.GetReadableVersion(versionInfo.Version));
-                    dialog.DetailsText = versionInfo.ReleaseNote;
+                using var dialog = new UpdateDialog();
 
-                    if (dialog.ShowDialog(this) == DialogResult.Yes)
-                    {
-                        await this.OpenUriInBrowserAsync(versionInfo.DownloadUri.OriginalString);
-                    }
-                    else if (dialog.SkipButtonPressed)
-                    {
-                        SettingManager.Common.SkipUpdateVersion = versionInfo.Version;
-                        this.MarkSettingCommonModified();
-                    }
+                dialog.SummaryText = string.Format(Properties.Resources.CheckNewVersionText3,
+                    MyCommon.GetReadableVersion(versionInfo.Version));
+                dialog.DetailsText = versionInfo.ReleaseNote;
+
+                if (dialog.ShowDialog(this) == DialogResult.Yes)
+                {
+                    await this.OpenUriInBrowserAsync(versionInfo.DownloadUri.OriginalString);
+                }
+                else if (dialog.SkipButtonPressed)
+                {
+                    SettingManager.Common.SkipUpdateVersion = versionInfo.Version;
+                    this.MarkSettingCommonModified();
                 }
             }
             catch (Exception)
@@ -5596,7 +5698,7 @@ namespace OpenTween
         /// <summary>
         /// サムネイル表示に使用する CancellationToken の生成元
         /// </summary>
-        private CancellationTokenSource thumbnailTokenSource = null;
+        private CancellationTokenSource? thumbnailTokenSource = null;
 
         private void DispSelectedPost(bool forceupdate)
         {
@@ -5622,7 +5724,7 @@ namespace OpenTween
                 var oldTokenSource = Interlocked.Exchange(ref this.thumbnailTokenSource, new CancellationTokenSource());
                 oldTokenSource?.Cancel();
 
-                var token = this.thumbnailTokenSource.Token;
+                var token = this.thumbnailTokenSource!.Token;
                 loadTasks.Add(this.tweetThumbnail1.ShowThumbnailAsync(currentPost, token));
             }
 
@@ -5653,7 +5755,7 @@ namespace OpenTween
             var tab = this.CurrentTab;
             if (tab.TabType == MyCommon.TabUsageType.PublicSearch)
             {
-                Control pnl = this.CurrentTabPage.Controls["panelSearch"];
+                var pnl = this.CurrentTabPage.Controls["panelSearch"];
                 if (pnl.Controls["comboSearch"].Focused ||
                     pnl.Controls["comboLang"].Focused ||
                     pnl.Controls["buttonSearch"].Focused) return;
@@ -5699,7 +5801,7 @@ namespace OpenTween
                     .Do(() => this.OpenApplicationWebsite()),
 
                 ShortcutCommand.Create(Keys.F3)
-                    .Do(() => this.MenuItemSearchNext_Click(null, null)),
+                    .Do(() => this.MenuItemSearchNext_Click(this.MenuItemSearchNext, EventArgs.Empty)),
 
                 ShortcutCommand.Create(Keys.F5)
                     .Do(() => this.DoRefresh()),
@@ -5712,11 +5814,11 @@ namespace OpenTween
 
                 ShortcutCommand.Create(Keys.Space, Keys.ProcessKey)
                     .NotFocusedOn(FocusedControl.StatusText)
-                    .Do(() => { this._anchorFlag = false; this.JumpUnreadMenuItem_Click(null, null); }),
+                    .Do(() => { this._anchorFlag = false; this.JumpUnreadMenuItem_Click(this.JumpUnreadMenuItem, EventArgs.Empty); }),
 
                 ShortcutCommand.Create(Keys.G)
                     .NotFocusedOn(FocusedControl.StatusText)
-                    .Do(() => { this._anchorFlag = false; this.ShowRelatedStatusesMenuItem_Click(null, null); }),
+                    .Do(() => { this._anchorFlag = false; this.ShowRelatedStatusesMenuItem_Click(this.ShowRelatedStatusesMenuItem, EventArgs.Empty); }),
 
                 ShortcutCommand.Create(Keys.Right, Keys.N)
                     .FocusedOn(FocusedControl.ListTab)
@@ -5815,35 +5917,35 @@ namespace OpenTween
                     .Do(() => this.doQuoteOfficial()),
 
                 ShortcutCommand.Create(Keys.Control | Keys.B)
-                    .Do(() => this.ReadedStripMenuItem_Click(null, null)),
+                    .Do(() => this.ReadedStripMenuItem_Click(this.ReadedStripMenuItem, EventArgs.Empty)),
 
                 ShortcutCommand.Create(Keys.Control | Keys.T)
-                    .Do(() => this.HashManageMenuItem_Click(null, null)),
+                    .Do(() => this.HashManageMenuItem_Click(this.HashManageMenuItem, EventArgs.Empty)),
 
                 ShortcutCommand.Create(Keys.Control | Keys.L)
-                    .Do(() => this.UrlConvertAutoToolStripMenuItem_Click(null, null)),
+                    .Do(() => this.UrlConvertAutoToolStripMenuItem_Click(this.UrlConvertAutoToolStripMenuItem, EventArgs.Empty)),
 
                 ShortcutCommand.Create(Keys.Control | Keys.Y)
                     .NotFocusedOn(FocusedControl.PostBrowser)
-                    .Do(() => this.MultiLineMenuItem_Click(null, null)),
+                    .Do(() => this.MultiLineMenuItem_Click(this.MultiLineMenuItem, EventArgs.Empty)),
 
                 ShortcutCommand.Create(Keys.Control | Keys.F)
-                    .Do(() => this.MenuItemSubSearch_Click(null, null)),
+                    .Do(() => this.MenuItemSubSearch_Click(this.MenuItemSubSearch, EventArgs.Empty)),
 
                 ShortcutCommand.Create(Keys.Control | Keys.U)
                     .Do(() => this.ShowUserTimeline()),
 
                 ShortcutCommand.Create(Keys.Control | Keys.H)
-                    .Do(() => this.MoveToHomeToolStripMenuItem_Click(null, null)),
+                    .Do(() => this.MoveToHomeToolStripMenuItem_Click(this.MoveToHomeToolStripMenuItem, EventArgs.Empty)),
 
                 ShortcutCommand.Create(Keys.Control | Keys.G)
-                    .Do(() => this.MoveToFavToolStripMenuItem_Click(null, null)),
+                    .Do(() => this.MoveToFavToolStripMenuItem_Click(this.MoveToFavToolStripMenuItem, EventArgs.Empty)),
 
                 ShortcutCommand.Create(Keys.Control | Keys.O)
-                    .Do(() => this.StatusOpenMenuItem_Click(null, null)),
+                    .Do(() => this.StatusOpenMenuItem_Click(this.StatusOpenMenuItem, EventArgs.Empty)),
 
                 ShortcutCommand.Create(Keys.Control | Keys.E)
-                    .Do(() => this.OpenURLMenuItem_Click(null, null)),
+                    .Do(() => this.OpenURLMenuItem_Click(this.OpenURLMenuItem, EventArgs.Empty)),
 
                 ShortcutCommand.Create(Keys.Control | Keys.Home, Keys.Control | Keys.End)
                     .FocusedOn(FocusedControl.ListTab)
@@ -5960,7 +6062,7 @@ namespace OpenTween
                     }),
 
                 ShortcutCommand.Create(Keys.Shift | Keys.F3)
-                    .Do(() => this.MenuItemSearchPrev_Click(null, null)),
+                    .Do(() => this.MenuItemSearchPrev_Click(this.MenuItemSearchPrev, EventArgs.Empty)),
 
                 ShortcutCommand.Create(Keys.Shift | Keys.F5)
                     .Do(() => this.DoRefreshMore()),
@@ -6022,7 +6124,7 @@ namespace OpenTween
 
                 ShortcutCommand.Create(Keys.Alt | Keys.P)
                     .OnlyWhen(() => this.CurrentPost != null)
-                    .Do(() => this.doShowUserStatus(this.CurrentPost.ScreenName, ShowInputDialog: false)),
+                    .Do(() => this.doShowUserStatus(this.CurrentPost!.ScreenName, ShowInputDialog: false)),
 
                 ShortcutCommand.Create(Keys.Alt | Keys.Up)
                     .Do(() => this.tweetDetailsView.ScrollDownPostBrowser(forward: false)),
@@ -6059,13 +6161,13 @@ namespace OpenTween
                     .Do(() => this.FavoriteChange(FavAdd: false)),
 
                 ShortcutCommand.Create(Keys.Control | Keys.Shift | Keys.B)
-                    .Do(() => this.UnreadStripMenuItem_Click(null, null)),
+                    .Do(() => this.UnreadStripMenuItem_Click(this.UnreadStripMenuItem, EventArgs.Empty)),
 
                 ShortcutCommand.Create(Keys.Control | Keys.Shift | Keys.T)
-                    .Do(() => this.HashToggleMenuItem_Click(null, null)),
+                    .Do(() => this.HashToggleMenuItem_Click(this.HashToggleMenuItem, EventArgs.Empty)),
 
                 ShortcutCommand.Create(Keys.Control | Keys.Shift | Keys.P)
-                    .Do(() => this.ImageSelectMenuItem_Click(null, null)),
+                    .Do(() => this.ImageSelectMenuItem_Click(this.ImageSelectMenuItem, EventArgs.Empty)),
 
                 ShortcutCommand.Create(Keys.Control | Keys.Shift | Keys.H)
                     .Do(() => this.doMoveToRTHome()),
@@ -6103,19 +6205,19 @@ namespace OpenTween
                     .Do(() => {
                         if (StatusText.SelectionStart > 0)
                         {
-                            int endidx = StatusText.SelectionStart - 1;
-                            string startstr = "";
-                            for (int i = StatusText.SelectionStart - 1; i >= 0; i--)
+                            var endidx = StatusText.SelectionStart - 1;
+                            var startstr = "";
+                            for (var i = StatusText.SelectionStart - 1; i >= 0; i--)
                             {
-                                char c = StatusText.Text[i];
-                                if (Char.IsLetterOrDigit(c) || c == '_')
+                                var c = StatusText.Text[i];
+                                if (char.IsLetterOrDigit(c) || c == '_')
                                 {
                                     continue;
                                 }
                                 if (c == '@')
                                 {
                                     startstr = StatusText.Text.Substring(i + 1, endidx - i);
-                                    int cnt = AtIdSupl.ItemCount;
+                                    var cnt = AtIdSupl.ItemCount;
                                     ShowSuplDialog(StatusText, AtIdSupl, startstr.Length + 1, startstr);
                                     if (AtIdSupl.ItemCount != cnt)
                                         this.MarkSettingAtIdModified();
@@ -6209,7 +6311,7 @@ namespace OpenTween
             };
         }
 
-        internal bool CommonKeyDown(Keys keyData, FocusedControl focusedOn, out Task asyncTask)
+        internal bool CommonKeyDown(Keys keyData, FocusedControl focusedOn, out Task? asyncTask)
         {
             // Task を返す非同期処理があれば asyncTask に代入する
             asyncTask = null;
@@ -6229,7 +6331,7 @@ namespace OpenTween
 
         private void GoNextTab(bool forward)
         {
-            int idx = this._statuses.SelectedTabIndex;
+            var idx = this._statuses.SelectedTabIndex;
             var tabCount = this._statuses.Tabs.Count;
             if (forward)
             {
@@ -6246,10 +6348,9 @@ namespace OpenTween
 
         private void CopyStot()
         {
-            string clstr = "";
-            StringBuilder sb = new StringBuilder();
+            var sb = new StringBuilder();
             var tab = this.CurrentTab;
-            bool IsProtected = false;
+            var IsProtected = false;
             var isDm = tab.TabType == MyCommon.TabUsageType.DirectMessage;
             foreach (var post in tab.SelectedPosts)
             {
@@ -6272,7 +6373,7 @@ namespace OpenTween
             }
             if (sb.Length > 0)
             {
-                clstr = sb.ToString();
+                var clstr = sb.ToString();
                 try
                 {
                     Clipboard.SetDataObject(clstr, false, 5, 100);
@@ -6315,9 +6416,9 @@ namespace OpenTween
 
             var selectedIndex = tab.SelectedIndex;
 
-            int fIdx = 0;
-            int toIdx = 0;
-            int stp = 1;
+            int fIdx;
+            int toIdx;
+            int stp;
 
             if (forward)
             {
@@ -6328,7 +6429,8 @@ namespace OpenTween
                 else
                 {
                     fIdx = selectedIndex + 1;
-                    if (fIdx > tab.AllCount - 1) return;
+                    if (fIdx > tab.AllCount - 1)
+                        return;
                 }
                 toIdx = tab.AllCount;
                 stp = 1;
@@ -6342,13 +6444,14 @@ namespace OpenTween
                 else
                 {
                     fIdx = selectedIndex - 1;
-                    if (fIdx < 0) return;
+                    if (fIdx < 0)
+                        return;
                 }
                 toIdx = -1;
                 stp = -1;
             }
 
-            for (int idx = fIdx; idx != toIdx; idx += stp)
+            for (var idx = fIdx; idx != toIdx; idx += stp)
             {
                 if (tab[idx].IsFav)
                 {
@@ -6403,7 +6506,7 @@ namespace OpenTween
                 stp = 1;
             }
 
-            for (int tabidx = fIdx; tabidx != toIdx; tabidx += stp)
+            for (var tabidx = fIdx; tabidx != toIdx; tabidx += stp)
             {
                 var targetTab = this._statuses.Tabs[tabidx];
 
@@ -6450,8 +6553,8 @@ namespace OpenTween
                 stp = -1;
             }
 
-            string name = "";
-            if (currentPost.RetweetedId == null)
+            string name;
+            if (currentPost.RetweetedBy == null)
             {
                 name = currentPost.ScreenName;
             }
@@ -6459,7 +6562,7 @@ namespace OpenTween
             {
                 name = currentPost.RetweetedBy;
             }
-            for (int idx = fIdx; idx != toIdx; idx += stp)
+            for (var idx = fIdx; idx != toIdx; idx += stp)
             {
                 var post = tab[idx];
                 if (post.RetweetedId == null)
@@ -6522,7 +6625,7 @@ namespace OpenTween
                 if (_anchorPost == null) return;
             }
 
-            for (int idx = fIdx; idx != toIdx; idx += stp)
+            for (var idx = fIdx; idx != toIdx; idx += stp)
             {
                 var post = tab[idx];
                 if (post.ScreenName == _anchorPost.ScreenName ||
@@ -6545,7 +6648,7 @@ namespace OpenTween
         private void GoAnchor()
         {
             if (_anchorPost == null) return;
-            int idx = this.CurrentTab.IndexOf(_anchorPost.StatusId);
+            var idx = this.CurrentTab.IndexOf(_anchorPost.StatusId);
             if (idx == -1) return;
 
             var listView = this.CurrentListView;
@@ -6637,7 +6740,7 @@ namespace OpenTween
         {
             var listView = this.CurrentListView;
             if (listView.SelectedIndices.Count == 0) return;
-            int idx = listView.SelectedIndices[0];
+            var idx = listView.SelectedIndices[0];
             if (_statuses.SortOrder == SortOrder.Ascending)
             {
                 listView.EnsureVisible(listView.VirtualListSize - 1);
@@ -6734,7 +6837,7 @@ namespace OpenTween
 
             var tabIndex = this._statuses.Tabs.IndexOf(inReplyToTabName);
             var tabPage = this.ListTab.TabPages[tabIndex];
-            DetailsListView listView = (DetailsListView)tabPage.Tag;
+            var listView = (DetailsListView)tabPage.Tag;
 
             if (this.CurrentTabName != inReplyToTabName)
             {
@@ -6768,17 +6871,17 @@ namespace OpenTween
                     try
                     {
                         var postList = posts.ToList();
-                        for (int i = postList.Count - 1; i >= 0; i--)
+                        for (var i = postList.Count - 1; i >= 0; i--)
                         {
-                            int index = i;
-                            if (postList.FindIndex((pst) => { return pst.Post.StatusId == postList[index].Post.StatusId; }) != index)
+                            var index = i;
+                            if (postList.FindIndex(pst => pst.Post.StatusId == postList[index].Post.StatusId) != index)
                             {
                                 postList.RemoveAt(index);
                             }
                         }
                         var currentIndex = this.CurrentTab.SelectedIndex;
-                        var post = postList.FirstOrDefault((pst) => { return pst.Tab == curTabClass && isForward ? pst.Index > currentIndex : pst.Index < currentIndex; });
-                        if (post == null) post = postList.FirstOrDefault((pst) => { return pst.Tab != curTabClass; });
+                        var post = postList.FirstOrDefault(pst => pst.Tab == curTabClass && isForward ? pst.Index > currentIndex : pst.Index < currentIndex);
+                        if (post == null) post = postList.FirstOrDefault(pst => pst.Tab != curTabClass);
                         if (post == null) post = postList.First();
                         var tabIndex = this._statuses.Tabs.IndexOf(post.Tab);
                         this.ListTab.SelectedIndex = tabIndex;
@@ -6820,7 +6923,7 @@ namespace OpenTween
                 }
                 else
                 {
-                    ReplyChain chainHead = replyChains.Pop();
+                    var chainHead = replyChains.Pop();
                     if (chainHead.InReplyToId == currentPost.StatusId)
                     {
                         var tab = chainHead.OriginalTab;
@@ -6866,7 +6969,7 @@ namespace OpenTween
             if (this.selectPostChains.Count > 1)
             {
                 var idx = -1;
-                TabModel foundTab = null;
+                TabModel? foundTab = null;
 
                 do
                 {
@@ -6924,7 +7027,7 @@ namespace OpenTween
             var currentTab = this.CurrentTab;
             var currentPost = this.CurrentPost;
 
-            int count = this.selectPostChains.Count;
+            var count = this.selectPostChains.Count;
             if (count > 0)
             {
                 var (tab, post) = this.selectPostChains.Peek();
@@ -6941,13 +7044,13 @@ namespace OpenTween
         private void TrimPostChain()
         {
             if (this.selectPostChains.Count <= 2000) return;
-            var p = new Stack<(TabModel, PostClass)>(2000);
-            for (int i = 0; i < 2000; i++)
+            var p = new Stack<(TabModel, PostClass?)>(2000);
+            for (var i = 0; i < 2000; i++)
             {
                 p.Push(this.selectPostChains.Pop());
             }
             this.selectPostChains.Clear();
-            for (int i = 0; i < 2000; i++)
+            for (var i = 0; i < 2000; i++)
             {
                 this.selectPostChains.Push(p.Pop());
             }
@@ -6981,7 +7084,7 @@ namespace OpenTween
         {
             if (statusId == 0) return false;
 
-            var tab = this._statuses.GetTabByType<DirectMessagesTabModel>();
+            var tab = this._statuses.DirectMessageTab;
             var index = tab.IndexOf(statusId);
 
             if (index == -1)
@@ -7028,7 +7131,7 @@ namespace OpenTween
                 e.SuppressKeyPress = true;
             }
 
-            this.StatusText_TextChanged(null, null);
+            this.StatusText_TextChanged(this.StatusText, EventArgs.Empty);
 
             if (asyncTask != null)
                 await asyncTask;
@@ -7227,7 +7330,7 @@ namespace OpenTween
         {
             var tab = this.CurrentTab;
 
-            DialogResult rslt = MessageBox.Show(string.Format(Properties.Resources.SaveLogMenuItem_ClickText1, Environment.NewLine),
+            var rslt = MessageBox.Show(string.Format(Properties.Resources.SaveLogMenuItem_ClickText1, Environment.NewLine),
                     Properties.Resources.SaveLogMenuItem_ClickText2,
                     MessageBoxButtons.YesNoCancel, MessageBoxIcon.Question);
             if (rslt == DialogResult.Cancel) return;
@@ -7242,52 +7345,52 @@ namespace OpenTween
             if (SaveFileDialog1.ShowDialog() == DialogResult.OK)
             {
                 if (!SaveFileDialog1.ValidateNames) return;
-                using (StreamWriter sw = new StreamWriter(SaveFileDialog1.FileName, false, Encoding.UTF8))
-                {
-                    if (rslt == DialogResult.Yes)
-                    {
-                        //All
-                        for (int idx = 0; idx < tab.AllCount; idx++)
-                        {
-                            var post = tab[idx];
-                            string protect = "";
-                            if (post.IsProtect) protect = "Protect";
-                            sw.WriteLine(post.Nickname + "\t" +
-                                     "\"" + post.TextFromApi.Replace("\n", "").Replace("\"", "\"\"") + "\"" + "\t" +
-                                     post.CreatedAt.ToLocalTimeString() + "\t" +
-                                     post.ScreenName + "\t" +
-                                     post.StatusId + "\t" +
-                                     post.ImageUrl + "\t" +
-                                     "\"" + post.Text.Replace("\n", "").Replace("\"", "\"\"") + "\"" + "\t" +
-                                     protect);
-                        }
+                using var sw = new StreamWriter(SaveFileDialog1.FileName, false, Encoding.UTF8);
+                if (rslt == DialogResult.Yes)
+                {
+                    //All
+                    for (var idx = 0; idx < tab.AllCount; idx++)
+                    {
+                        var post = tab[idx];
+                        var protect = "";
+                        if (post.IsProtect)
+                            protect = "Protect";
+                        sw.WriteLine(post.Nickname + "\t" +
+                                 "\"" + post.TextFromApi.Replace("\n", "").Replace("\"", "\"\"") + "\"" + "\t" +
+                                 post.CreatedAt.ToLocalTimeString() + "\t" +
+                                 post.ScreenName + "\t" +
+                                 post.StatusId + "\t" +
+                                 post.ImageUrl + "\t" +
+                                 "\"" + post.Text.Replace("\n", "").Replace("\"", "\"\"") + "\"" + "\t" +
+                                 protect);
                     }
-                    else
+                }
+                else
+                {
+                    foreach (var post in this.CurrentTab.SelectedPosts)
                     {
-                        foreach (var post in this.CurrentTab.SelectedPosts)
-                        {
-                            string protect = "";
-                            if (post.IsProtect) protect = "Protect";
-                            sw.WriteLine(post.Nickname + "\t" +
-                                     "\"" + post.TextFromApi.Replace("\n", "").Replace("\"", "\"\"") + "\"" + "\t" +
-                                     post.CreatedAt.ToLocalTimeString() + "\t" +
-                                     post.ScreenName + "\t" +
-                                     post.StatusId + "\t" +
-                                     post.ImageUrl + "\t" +
-                                     "\"" + post.Text.Replace("\n", "").Replace("\"", "\"\"") + "\"" + "\t" +
-                                     protect);
-                        }
+                        var protect = "";
+                        if (post.IsProtect)
+                            protect = "Protect";
+                        sw.WriteLine(post.Nickname + "\t" +
+                                 "\"" + post.TextFromApi.Replace("\n", "").Replace("\"", "\"\"") + "\"" + "\t" +
+                                 post.CreatedAt.ToLocalTimeString() + "\t" +
+                                 post.ScreenName + "\t" +
+                                 post.StatusId + "\t" +
+                                 post.ImageUrl + "\t" +
+                                 "\"" + post.Text.Replace("\n", "").Replace("\"", "\"\"") + "\"" + "\t" +
+                                 protect);
                     }
                 }
             }
             this.TopMost = SettingManager.Common.AlwaysTop;
         }
 
-        public bool TabRename(string origTabName, out string newTabName)
+        public bool TabRename(string origTabName, [NotNullWhen(true)] out string? newTabName)
         {
             //タブ名変更
             newTabName = null;
-            using (InputTabName inputName = new InputTabName())
+            using (var inputName = new InputTabName())
             {
                 inputName.TabName = origTabName;
                 inputName.ShowDialog();
@@ -7300,7 +7403,7 @@ namespace OpenTween
                 //新タブ名存在チェック
                 if (this._statuses.ContainsTab(newTabName))
                 {
-                    string tmp = string.Format(Properties.Resources.Tabs_DoubleClickText1, newTabName);
+                    var tmp = string.Format(Properties.Resources.Tabs_DoubleClickText1, newTabName);
                     MessageBox.Show(tmp, Properties.Resources.Tabs_DoubleClickText2, MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
                     return false;
                 }
@@ -7342,7 +7445,7 @@ namespace OpenTween
         }
 
         private void ListTab_DoubleClick(object sender, MouseEventArgs e)
-            => this.TabRename(this.CurrentTabName, out var _);
+            => this.TabRename(this.CurrentTabName, out _);
 
         private void ListTab_MouseDown(object sender, MouseEventArgs e)
         {
@@ -7378,13 +7481,13 @@ namespace OpenTween
             if (!e.Data.GetDataPresent(typeof(TabPage))) return;
 
             _tabDrag = false;
-            string tn = "";
-            bool bef = false;
-            Point cpos = new Point(e.X, e.Y);
-            Point spos = ListTab.PointToClient(cpos);
+            var tn = "";
+            var bef = false;
+            var cpos = new Point(e.X, e.Y);
+            var spos = ListTab.PointToClient(cpos);
             foreach (var (tab, index) in this._statuses.Tabs.WithIndex())
             {
-                Rectangle rect = ListTab.GetTabRect(index);
+                var rect = ListTab.GetTabRect(index);
                 if (rect.Contains(spos))
                 {
                     tn = tab.TabName;
@@ -7405,7 +7508,7 @@ namespace OpenTween
                 bef = false;
             }
 
-            TabPage tp = (TabPage)e.Data.GetData(typeof(TabPage));
+            var tp = (TabPage)e.Data.GetData(typeof(TabPage));
             if (tp.Text == tn) return;
 
             ReOrderTab(tp.Text, tn, bef);
@@ -7531,8 +7634,8 @@ namespace OpenTween
                         else
                         {
                             //1件選んでCtrl-Rの場合(返信先操作せず)
-                            int sidx = StatusText.SelectionStart;
-                            string id = "@" + post.ScreenName + " ";
+                            var sidx = StatusText.SelectionStart;
+                            var id = "@" + post.ScreenName + " ";
                             if (sidx > 0)
                             {
                                 if (StatusText.Text.Substring(sidx - 1, 1) != " ")
@@ -7573,7 +7676,7 @@ namespace OpenTween
                     {
                         //Enter or DoubleClick
 
-                        string sTxt = StatusText.Text;
+                        var sTxt = StatusText.Text;
                         if (!sTxt.StartsWith(". ", StringComparison.Ordinal))
                         {
                             sTxt = ". " + sTxt;
@@ -7597,8 +7700,8 @@ namespace OpenTween
                         {
                             //複数ポスト選択
 
-                            string ids = "";
-                            int sidx = StatusText.SelectionStart;
+                            var ids = "";
+                            var sidx = StatusText.SelectionStart;
                             foreach (var post in selectedPosts)
                             {
                                 if (!ids.Contains("@" + post.ScreenName + " ") && post.UserId != tw.UserId)
@@ -7612,7 +7715,7 @@ namespace OpenTween
                                         if (!ids.Contains("@" + screenName + " ") &&
                                             !screenName.Equals(tw.Username, StringComparison.CurrentCultureIgnoreCase))
                                         {
-                                            Match m = Regex.Match(post.TextFromApi, "[@@](?<id>" + screenName + ")([^a-zA-Z0-9]|$)", RegexOptions.IgnoreCase);
+                                            var m = Regex.Match(post.TextFromApi, "[@@](?<id>" + screenName + ")([^a-zA-Z0-9]|$)", RegexOptions.IgnoreCase);
                                             if (m.Success)
                                                 ids += "@" + m.Result("${id}") + " ";
                                             else
@@ -7655,8 +7758,8 @@ namespace OpenTween
                         {
                             //1件のみ選択のC-S-r(返信元付加する可能性あり)
 
-                            string ids = "";
-                            int sidx = StatusText.SelectionStart;
+                            var ids = "";
+                            var sidx = StatusText.SelectionStart;
                             var post = selectedPosts.Single();
                             if (!ids.Contains("@" + post.ScreenName + " ") && post.UserId != tw.UserId)
                             {
@@ -7667,7 +7770,7 @@ namespace OpenTween
                                 if (!ids.Contains("@" + screenName + " ") &&
                                     !screenName.Equals(tw.Username, StringComparison.CurrentCultureIgnoreCase))
                                 {
-                                    Match m = Regex.Match(post.TextFromApi, "[@@](?<id>" + screenName + ")([^a-zA-Z0-9]|$)", RegexOptions.IgnoreCase);
+                                    var m = Regex.Match(post.TextFromApi, "[@@](?<id>" + screenName + ")([^a-zA-Z0-9]|$)", RegexOptions.IgnoreCase);
                                     if (m.Success)
                                         ids += "@" + m.Result("${id}") + " ";
                                     else
@@ -7807,17 +7910,17 @@ namespace OpenTween
             this.SoundFileTbComboBox.Items.Clear();
             SoundFileComboBox.Items.Add("");
             this.SoundFileTbComboBox.Items.Add("");
-            DirectoryInfo oDir = new DirectoryInfo(Application.StartupPath + Path.DirectorySeparatorChar);
+            var oDir = new DirectoryInfo(Application.StartupPath + Path.DirectorySeparatorChar);
             if (Directory.Exists(Path.Combine(Application.StartupPath, "Sounds")))
             {
                 oDir = oDir.GetDirectories("Sounds")[0];
             }
-            foreach (FileInfo oFile in oDir.GetFiles("*.wav"))
+            foreach (var oFile in oDir.GetFiles("*.wav"))
             {
                 SoundFileComboBox.Items.Add(oFile.Name);
                 this.SoundFileTbComboBox.Items.Add(oFile.Name);
             }
-            int idx = SoundFileComboBox.Items.IndexOf(tb.SoundFile);
+            var idx = SoundFileComboBox.Items.IndexOf(tb.SoundFile);
             if (idx == -1) idx = 0;
             SoundFileComboBox.SelectedIndex = idx;
             this.SoundFileTbComboBox.SelectedIndex = idx;
@@ -7830,7 +7933,7 @@ namespace OpenTween
 
         private void TabMenuControl(string tabName)
         {
-            var tabInfo = _statuses.GetTabByName(tabName);
+            var tabInfo = _statuses.GetTabByName(tabName)!;
 
             this.FilterEditMenuItem.Enabled = true;
             this.EditRuleTbMenuItem.Enabled = true;
@@ -7952,7 +8055,7 @@ namespace OpenTween
 
         private void FilterEditMenuItem_Click(object sender, EventArgs e)
         {
-            if (string.IsNullOrEmpty(_rclickTabName)) _rclickTabName = _statuses.GetTabByType(MyCommon.TabUsageType.Home).TabName;
+            if (string.IsNullOrEmpty(_rclickTabName)) _rclickTabName = _statuses.HomeTab.TabName;
 
             using (var fltDialog = new FilterDialog())
             {
@@ -7968,9 +8071,9 @@ namespace OpenTween
 
         private async void AddTabMenuItem_Click(object sender, EventArgs e)
         {
-            string tabName = null;
+            string? tabName = null;
             MyCommon.TabUsageType tabUsage;
-            using (InputTabName inputName = new InputTabName())
+            using (var inputName = new InputTabName())
             {
                 inputName.TabName = _statuses.MakeTabName("MyTab");
                 inputName.IsShowUsage = true;
@@ -7983,15 +8086,15 @@ namespace OpenTween
             if (!string.IsNullOrEmpty(tabName))
             {
                 //List対応
-                ListElement list = null;
+                ListElement? list = null;
                 if (tabUsage == MyCommon.TabUsageType.Lists)
                 {
-                    using (ListAvailable listAvail = new ListAvailable())
-                    {
-                        if (listAvail.ShowDialog(this) == DialogResult.Cancel) return;
-                        if (listAvail.SelectedList == null) return;
-                        list = listAvail.SelectedList;
-                    }
+                    using var listAvail = new ListAvailable();
+                    if (listAvail.ShowDialog(this) == DialogResult.Cancel)
+                        return;
+                    if (listAvail.SelectedList == null)
+                        return;
+                    list = listAvail.SelectedList;
                 }
 
                 TabModel tab;
@@ -8004,7 +8107,7 @@ namespace OpenTween
                         tab = new PublicSearchTabModel(tabName);
                         break;
                     case MyCommon.TabUsageType.Lists:
-                        tab = new ListTimelineTabModel(tabName, list);
+                        tab = new ListTimelineTabModel(tabName, list!);
                         break;
                     default:
                         return;
@@ -8012,7 +8115,7 @@ namespace OpenTween
 
                 if (!_statuses.AddTab(tab) || !AddNewTab(tab, startup: false))
                 {
-                    string tmp = string.Format(Properties.Resources.AddTabMenuItem_ClickText1, tabName);
+                    var tmp = string.Format(Properties.Resources.AddTabMenuItem_ClickText1, tabName);
                     MessageBox.Show(tmp, Properties.Resources.AddTabMenuItem_ClickText2, MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
                 }
                 else
@@ -8050,7 +8153,7 @@ namespace OpenTween
 
                     fltDialog.SetCurrent(tabName);
 
-                    if (post.RetweetedId == null)
+                    if (post.RetweetedBy == null)
                     {
                         fltDialog.AddNewFilter(post.ScreenName, post.TextFromApi);
                     }
@@ -8074,8 +8177,8 @@ namespace OpenTween
             {
                 if (StatusText.Focused)
                 {
-                    bool _NewLine = false;
-                    bool _Post = false;
+                    var _NewLine = false;
+                    var _Post = false;
 
                     if (SettingManager.Common.PostCtrlEnter) //Ctrl+Enter投稿時
                     {
@@ -8124,7 +8227,7 @@ namespace OpenTween
 
                     if (_NewLine)
                     {
-                        int pos1 = StatusText.SelectionStart;
+                        var pos1 = StatusText.SelectionStart;
                         if (StatusText.SelectionLength > 0)
                         {
                             StatusText.Text = StatusText.Text.Remove(pos1, StatusText.SelectionLength);  //選択状態文字列削除
@@ -8135,7 +8238,7 @@ namespace OpenTween
                     }
                     else if (_Post)
                     {
-                        PostButton_Click(null, null);
+                        PostButton_Click(this.PostButton, EventArgs.Empty);
                         return true;
                     }
                 }
@@ -8148,7 +8251,7 @@ namespace OpenTween
                         if (tabPage.Controls["panelSearch"].Controls["comboSearch"].Focused ||
                             tabPage.Controls["panelSearch"].Controls["comboLang"].Focused)
                         {
-                            this.SearchButton_Click(tabPage.Controls["panelSearch"].Controls["comboSearch"], null);
+                            this.SearchButton_Click(tabPage.Controls["panelSearch"].Controls["comboSearch"], EventArgs.Empty);
                             return true;
                         }
                     }
@@ -8171,19 +8274,19 @@ namespace OpenTween
                 return;
 
             var screenNameArray = selectedPosts
-                .Select(x => x.RetweetedId != null ? x.RetweetedBy : x.ScreenName)
+                .Select(x => x.RetweetedBy ?? x.ScreenName)
                 .ToArray();
 
             this.AddFilterRuleByScreenName(screenNameArray);
 
             if (screenNameArray.Length != 0)
             {
-                List<string> atids = new List<string>();
+                var atids = new List<string>();
                 foreach (var screenName in screenNameArray)
                 {
                     atids.Add("@" + screenName);
                 }
-                int cnt = AtIdSupl.ItemCount;
+                var cnt = AtIdSupl.ItemCount;
                 AtIdSupl.AddRangeItem(atids.ToArray());
                 if (AtIdSupl.ItemCount != cnt)
                     this.MarkSettingAtIdModified();
@@ -8279,7 +8382,7 @@ namespace OpenTween
             this.SaveConfigsTabs();
         }
 
-        private bool SelectTab(out string tabName)
+        private bool SelectTab([NotNullWhen(true)] out string? tabName)
         {
             do
             {
@@ -8297,7 +8400,7 @@ namespace OpenTween
                 //新規タブを選択→タブ作成
                 if (tabName == null)
                 {
-                    using (InputTabName inputName = new InputTabName())
+                    using (var inputName = new InputTabName())
                     {
                         inputName.TabName = _statuses.MakeTabName("MyTab");
                         inputName.ShowDialog();
@@ -8310,7 +8413,7 @@ namespace OpenTween
                         var tab = new FilterTabModel(tabName);
                         if (!_statuses.AddTab(tab) || !AddNewTab(tab, startup: false))
                         {
-                            string tmp = string.Format(Properties.Resources.IDRuleMenuItem_ClickText2, tabName);
+                            var tmp = string.Format(Properties.Resources.IDRuleMenuItem_ClickText2, tabName);
                             MessageBox.Show(tmp, Properties.Resources.IDRuleMenuItem_ClickText3, MessageBoxButtons.OK, MessageBoxIcon.Exclamation);
                             //もう一度タブ名入力
                         }
@@ -8333,7 +8436,7 @@ namespace OpenTween
         {
             {
                 //移動するか?
-                string _tmp = string.Format(Properties.Resources.IDRuleMenuItem_ClickText4, Environment.NewLine);
+                var _tmp = string.Format(Properties.Resources.IDRuleMenuItem_ClickText4, Environment.NewLine);
                 if (MessageBox.Show(_tmp, Properties.Resources.IDRuleMenuItem_ClickText5, MessageBoxButtons.YesNo, MessageBoxIcon.Question) == DialogResult.Yes)
                     move = false;
                 else
@@ -8342,7 +8445,7 @@ namespace OpenTween
             if (!move)
             {
                 //マークするか?
-                string _tmp = string.Format(Properties.Resources.IDRuleMenuItem_ClickText6, Environment.NewLine);
+                var _tmp = string.Format(Properties.Resources.IDRuleMenuItem_ClickText6, Environment.NewLine);
                 if (MessageBox.Show(_tmp, Properties.Resources.IDRuleMenuItem_ClickText7, MessageBoxButtons.YesNo, MessageBoxIcon.Question) == DialogResult.Yes)
                     mark = true;
                 else
@@ -8383,7 +8486,7 @@ namespace OpenTween
             var listView = this.CurrentListView;
             if (listView.SelectedIndices.Count == 0) return;
 
-            int idx = listView.SelectedIndices[0];
+            var idx = listView.SelectedIndices[0];
 
             _item = listView.GetItemAt(0, 25);
             if (_item == null)
@@ -8470,7 +8573,7 @@ namespace OpenTween
         {
             if (showWarning)
             {
-                string tmp = string.Format(Properties.Resources.ClearTabMenuItem_ClickText1, Environment.NewLine);
+                var tmp = string.Format(Properties.Resources.ClearTabMenuItem_ClickText1, Environment.NewLine);
                 if (MessageBox.Show(tmp, tabName + " " + Properties.Resources.ClearTabMenuItem_ClickText2, MessageBoxButtons.OKCancel, MessageBoxIcon.Question) == DialogResult.Cancel)
                 {
                     return;
@@ -8503,9 +8606,9 @@ namespace OpenTween
         private void SetMainWindowTitle()
         {
             //メインウインドウタイトルの書き換え
-            StringBuilder ttl = new StringBuilder(256);
-            int ur = 0;
-            int al = 0;
+            var ttl = new StringBuilder(256);
+            var ur = 0;
+            var al = 0;
             if (SettingManager.Common.DispLatestPost != MyCommon.DispTitleEnum.None &&
                 SettingManager.Common.DispLatestPost != MyCommon.DispTitleEnum.Post &&
                 SettingManager.Common.DispLatestPost != MyCommon.DispTitleEnum.Ver &&
@@ -8531,13 +8634,13 @@ namespace OpenTween
                         ttl.Append(_history[_history.Count - 2].status.Replace("\r\n", " "));
                     break;
                 case MyCommon.DispTitleEnum.UnreadRepCount:
-                    ttl.AppendFormat(Properties.Resources.SetMainWindowTitleText1, _statuses.GetTabByType(MyCommon.TabUsageType.Mentions).UnreadCount + _statuses.GetTabByType(MyCommon.TabUsageType.DirectMessage).UnreadCount);
+                    ttl.AppendFormat(Properties.Resources.SetMainWindowTitleText1, _statuses.MentionTab.UnreadCount + _statuses.DirectMessageTab.UnreadCount);
                     break;
                 case MyCommon.DispTitleEnum.UnreadAllCount:
                     ttl.AppendFormat(Properties.Resources.SetMainWindowTitleText2, ur);
                     break;
                 case MyCommon.DispTitleEnum.UnreadAllRepCount:
-                    ttl.AppendFormat(Properties.Resources.SetMainWindowTitleText3, ur, _statuses.GetTabByType(MyCommon.TabUsageType.Mentions).UnreadCount + _statuses.GetTabByType(MyCommon.TabUsageType.DirectMessage).UnreadCount);
+                    ttl.AppendFormat(Properties.Resources.SetMainWindowTitleText3, ur, _statuses.MentionTab.UnreadCount + _statuses.DirectMessageTab.UnreadCount);
                     break;
                 case MyCommon.DispTitleEnum.UnreadCountAllCount:
                     ttl.AppendFormat(Properties.Resources.SetMainWindowTitleText4, ur, al);
@@ -8563,15 +8666,15 @@ namespace OpenTween
             //ステータス欄にカウント表示
             //タブ未読数/タブ発言数 全未読数/総発言数 (未読@+未読DM数)
             if (_statuses == null) return "";
-            TabModel tbRep = _statuses.GetTabByType(MyCommon.TabUsageType.Mentions);
-            TabModel tbDm = _statuses.GetTabByType(MyCommon.TabUsageType.DirectMessage);
+            var tbRep = _statuses.MentionTab;
+            var tbDm = _statuses.DirectMessageTab;
             if (tbRep == null || tbDm == null) return "";
-            int urat = tbRep.UnreadCount + tbDm.UnreadCount;
-            int ur = 0;
-            int al = 0;
-            int tur = 0;
-            int tal = 0;
-            StringBuilder slbl = new StringBuilder(256);
+            var urat = tbRep.UnreadCount + tbDm.UnreadCount;
+            var ur = 0;
+            var al = 0;
+            var tur = 0;
+            var tal = 0;
+            var slbl = new StringBuilder(256);
             try
             {
                 foreach (var tab in _statuses.Tabs)
@@ -8593,7 +8696,7 @@ namespace OpenTween
             UnreadCounter = ur;
             UnreadAtCounter = urat;
 
-            var homeTab = this._statuses.GetTabByType<HomeTabModel>();
+            var homeTab = this._statuses.HomeTab;
 
             slbl.AppendFormat(Properties.Resources.SetStatusLabelText1, tur, tal, ur, al, urat, _postTimestamps.Count, _favTimestamps.Count, homeTab.TweetsPerHour);
             if (SettingManager.Common.TimelinePeriod == 0)
@@ -8617,7 +8720,7 @@ namespace OpenTween
                 }
                 else
                 {
-                    var endpointName = (e as TwitterApiStatus.AccessLimitUpdatedEventArgs).EndpointName;
+                    var endpointName = ((TwitterApiStatus.AccessLimitUpdatedEventArgs)e).EndpointName;
                     SetApiStatusLabel(endpointName);
                 }
             }
@@ -8631,7 +8734,7 @@ namespace OpenTween
             }
         }
 
-        private void SetApiStatusLabel(string endpointName = null)
+        private void SetApiStatusLabel(string? endpointName = null)
         {
             var tabType = this.CurrentTab.TabType;
 
@@ -8768,7 +8871,7 @@ namespace OpenTween
             MatchCollection m;
             //ハッシュタグの保存
             m = Regex.Matches(StatusText, Twitter.HASHTAG, RegexOptions.IgnoreCase);
-            string hstr = "";
+            var hstr = "";
             foreach (Match hm in m)
             {
                 if (!hstr.Contains("#" + hm.Result("$3") + " "))
@@ -8788,7 +8891,7 @@ namespace OpenTween
 
             if (SettingManager.Common.UseAtIdSupplement)
             {
-                int bCnt = AtIdSupl.ItemCount;
+                var bCnt = AtIdSupl.ItemCount;
                 foreach (Match mid in m)
                 {
                     AtIdSupl.AddItem(mid.Result("${id}"));
@@ -8852,7 +8955,7 @@ namespace OpenTween
                 if (StatusText.Multiline)
                 {
                     var statusTextHeight = ScaleBy(configScaleFactor.Height, SettingManager.Local.StatusTextHeight);
-                    int dis = SplitContainer2.Height - statusTextHeight - SplitContainer2.SplitterWidth;
+                    var dis = SplitContainer2.Height - statusTextHeight - SplitContainer2.SplitterWidth;
                     if (dis > SplitContainer2.Panel1MinSize && dis < SplitContainer2.Height - SplitContainer2.Panel2MinSize - SplitContainer2.SplitterWidth)
                     {
                         SplitContainer2.SplitterDistance = SplitContainer2.Height - statusTextHeight - SplitContainer2.SplitterWidth;
@@ -8927,24 +9030,23 @@ namespace OpenTween
         private async Task doRepliedStatusOpen()
         {
             var currentPost = this.CurrentPost;
-            if (this.ExistCurrentPost && currentPost.InReplyToUser != null && currentPost.InReplyToStatusId != null)
+            if (this.ExistCurrentPost && currentPost != null && currentPost.InReplyToUser != null && currentPost.InReplyToStatusId != null)
             {
                 if (MyCommon.IsKeyDown(Keys.Shift))
                 {
                     await this.OpenUriInBrowserAsync(MyCommon.GetStatusUrl(currentPost.InReplyToUser, currentPost.InReplyToStatusId.Value));
                     return;
                 }
-                if (_statuses.ContainsKey(currentPost.InReplyToStatusId.Value))
+                if (this._statuses.Posts.TryGetValue(currentPost.InReplyToStatusId.Value, out var repPost))
                 {
-                    PostClass repPost = _statuses[currentPost.InReplyToStatusId.Value];
                     MessageBox.Show($"{repPost.ScreenName} / {repPost.Nickname}   ({repPost.CreatedAt.ToLocalTimeString()})" + Environment.NewLine + repPost.TextFromApi);
                 }
                 else
                 {
-                    foreach (TabModel tb in _statuses.GetTabsByType(MyCommon.TabUsageType.Lists | MyCommon.TabUsageType.PublicSearch))
+                    foreach (var tb in _statuses.GetTabsByType(MyCommon.TabUsageType.Lists | MyCommon.TabUsageType.PublicSearch))
                     {
                         if (tb == null || !tb.Contains(currentPost.InReplyToStatusId.Value)) break;
-                        PostClass repPost = _statuses[currentPost.InReplyToStatusId.Value];
+                        repPost = tb.Posts[currentPost.InReplyToStatusId.Value];
                         MessageBox.Show($"{repPost.ScreenName} / {repPost.Nickname}   ({repPost.CreatedAt.ToLocalTimeString()})" + Environment.NewLine + repPost.TextFromApi);
                         return;
                     }
@@ -9022,13 +9124,12 @@ namespace OpenTween
             //Appendix A.  Collected ABNF for URI
             //http://www.ietf.org/rfc/rfc3986.txt
 
-            string result = "";
-
             const string nico = @"^https?://[a-z]+\.(nicovideo|niconicommons|nicolive)\.jp/[a-z]+/[a-z0-9]+$";
 
+            string result;
             if (StatusText.SelectionLength > 0)
             {
-                string tmp = StatusText.SelectedText;
+                var tmp = StatusText.SelectedText;
                 // httpから始まらない場合、ExcludeStringで指定された文字列で始まる場合は対象としない
                 if (tmp.StartsWith("http", StringComparison.OrdinalIgnoreCase))
                 {
@@ -9066,7 +9167,7 @@ namespace OpenTween
 
                     if (!string.IsNullOrEmpty(result))
                     {
-                        urlUndo undotmp = new urlUndo();
+                        var undotmp = new urlUndo();
 
                         // 短縮 URL が生成されるまでの間に投稿欄から元の URL が削除されていたら中断する
                         var origUrlIndex = this.StatusText.Text.IndexOf(tmp, StringComparison.Ordinal);
@@ -9100,10 +9201,12 @@ namespace OpenTween
                 // 正規表現にマッチしたURL文字列をtinyurl化
                 foreach (Match mt in Regex.Matches(StatusText.Text, url, RegexOptions.IgnoreCase))
                 {
-                    if (StatusText.Text.IndexOf(mt.Result("${url}"), StringComparison.Ordinal) == -1) continue;
-                    string tmp = mt.Result("${url}");
-                    if (tmp.StartsWith("w", StringComparison.OrdinalIgnoreCase)) tmp = "http://" + tmp;
-                    urlUndo undotmp = new urlUndo();
+                    if (StatusText.Text.IndexOf(mt.Result("${url}"), StringComparison.Ordinal) == -1)
+                        continue;
+                    var tmp = mt.Result("${url}");
+                    if (tmp.StartsWith("w", StringComparison.OrdinalIgnoreCase))
+                        tmp = "http://" + tmp;
+                    var undotmp = new urlUndo();
 
                     //選んだURLを選択(?)
                     StatusText.Select(StatusText.Text.IndexOf(mt.Result("${url}"), StringComparison.Ordinal), mt.Result("${url}").Length);
@@ -9178,8 +9281,8 @@ namespace OpenTween
         {
             if (urlUndoBuffer != null)
             {
-                string tmp = StatusText.Text;
-                foreach (urlUndo data in urlUndoBuffer)
+                var tmp = StatusText.Text;
+                foreach (var data in urlUndoBuffer)
                 {
                     tmp = tmp.Replace(data.After, data.Before);
                 }
@@ -9204,8 +9307,9 @@ namespace OpenTween
         {
             if (!await UrlConvertAsync(SettingManager.Common.AutoShortUrlFirst))
             {
-                MyCommon.UrlConverter svc = SettingManager.Common.AutoShortUrlFirst;
-                Random rnd = new Random();
+                var rnd = new Random();
+
+                MyCommon.UrlConverter svc;
                 // 前回使用した短縮URLサービス以外を選択する
                 do
                 {
@@ -9238,7 +9342,7 @@ namespace OpenTween
         private void MenuStrip1_MenuActivate(object sender, EventArgs e)
         {
             // フォーカスがメニューに移る (MenuStrip1.Tag フラグを立てる)
-            MenuStrip1.Tag = new Object();
+            MenuStrip1.Tag = new object();
             MenuStrip1.Select(); // StatusText がフォーカスを持っている場合 Leave が発生
         }
 
@@ -9263,7 +9367,7 @@ namespace OpenTween
 
         private void MyList_ColumnReordered(object sender, ColumnReorderedEventArgs e)
         {
-            DetailsListView lst = (DetailsListView)sender;
+            var lst = (DetailsListView)sender;
             if (SettingManager.Local == null) return;
 
             if (_iconCol)
@@ -9273,14 +9377,14 @@ namespace OpenTween
             }
             else
             {
-                int[] darr = new int[lst.Columns.Count];
-                for (int i = 0; i < lst.Columns.Count; i++)
+                var darr = new int[lst.Columns.Count];
+                for (var i = 0; i < lst.Columns.Count; i++)
                 {
                     darr[lst.Columns[i].DisplayIndex] = i;
                 }
                 MyCommon.MoveArrayItem(darr, e.OldDisplayIndex, e.NewDisplayIndex);
 
-                for (int i = 0; i < lst.Columns.Count; i++)
+                for (var i = 0; i < lst.Columns.Count; i++)
                 {
                     switch (darr[i])
                     {
@@ -9325,7 +9429,7 @@ namespace OpenTween
 
         private void MyList_ColumnWidthChanged(object sender, ColumnWidthChangedEventArgs e)
         {
-            DetailsListView lst = (DetailsListView)sender;
+            var lst = (DetailsListView)sender;
             if (SettingManager.Local == null) return;
 
             var modified = false;
@@ -9435,7 +9539,7 @@ namespace OpenTween
             }
             else if (e.Data.GetDataPresent(DataFormats.StringFormat))
             {
-                string data = (string)e.Data.GetData(DataFormats.StringFormat, true);
+                var data = (string)e.Data.GetData(DataFormats.StringFormat, true);
                 if (data != null) StatusText.Text += data;
             }
         }
@@ -9448,45 +9552,39 @@ namespace OpenTween
         /// </remarks>
         /// <exception cref="ArgumentException">不正なフォーマットが入力された場合</exception>
         /// <exception cref="NotSupportedException">サポートされていないデータが入力された場合</exception>
-        internal static (string Url, string Title) GetUrlFromDataObject(IDataObject data)
+        internal static (string Url, string? Title) GetUrlFromDataObject(IDataObject data)
         {
             if (data.GetDataPresent("text/x-moz-url"))
             {
                 // Firefox, Google Chrome で利用可能
                 // 参照: https://developer.mozilla.org/ja/docs/DragDrop/Recommended_Drag_Types
 
-                using (var stream = (MemoryStream)data.GetData("text/x-moz-url"))
-                {
-                    var lines = Encoding.Unicode.GetString(stream.ToArray()).TrimEnd('\0').Split('\n');
-                    if (lines.Length < 2)
-                        throw new ArgumentException("不正な text/x-moz-url フォーマットです", nameof(data));
+                using var stream = (MemoryStream)data.GetData("text/x-moz-url");
+                var lines = Encoding.Unicode.GetString(stream.ToArray()).TrimEnd('\0').Split('\n');
+                if (lines.Length < 2)
+                    throw new ArgumentException("不正な text/x-moz-url フォーマットです", nameof(data));
 
-                    return (lines[0], lines[1]);
-                }
+                return (lines[0], lines[1]);
             }
             else if (data.GetDataPresent("IESiteModeToUrl"))
             {
                 // Internet Exproler 用
                 // 保護モードが有効なデフォルトの IE では DragDrop イベントが発火しないため使えない
 
-                using (var stream = (MemoryStream)data.GetData("IESiteModeToUrl"))
-                {
-                    var lines = Encoding.Unicode.GetString(stream.ToArray()).TrimEnd('\0').Split('\0');
-                    if (lines.Length < 2)
-                        throw new ArgumentException("不正な IESiteModeToUrl フォーマットです", nameof(data));
+                using var stream = (MemoryStream)data.GetData("IESiteModeToUrl");
+                var lines = Encoding.Unicode.GetString(stream.ToArray()).TrimEnd('\0').Split('\0');
+                if (lines.Length < 2)
+                    throw new ArgumentException("不正な IESiteModeToUrl フォーマットです", nameof(data));
 
-                    return (lines[0], lines[1]);
-                }
+                return (lines[0], lines[1]);
             }
             else if (data.GetDataPresent("UniformResourceLocatorW"))
             {
                 // それ以外のブラウザ向け
 
-                using (var stream = (MemoryStream)data.GetData("UniformResourceLocatorW"))
-                {
-                    var url = Encoding.Unicode.GetString(stream.ToArray()).TrimEnd('\0');
-                    return (url, null);
-                }
+                using var stream = (MemoryStream)data.GetData("UniformResourceLocatorW");
+                var url = Encoding.Unicode.GetString(stream.ToArray()).TrimEnd('\0');
+                return (url, null);
             }
 
             throw new NotSupportedException("サポートされていないデータ形式です: " + data.GetFormats()[0]);
@@ -9527,8 +9625,7 @@ namespace OpenTween
 
         public bool IsNetworkAvailable()
         {
-            bool nw = true;
-            nw = MyCommon.IsNetworkAvailable();
+            var nw = MyCommon.IsNetworkAvailable();
             _myStatusOnline = nw;
             return nw;
         }
@@ -9599,7 +9696,7 @@ namespace OpenTween
         {
             return Task.Run(() =>
             {
-                string myPath = UriString;
+                var myPath = UriString;
 
                 try
                 {
@@ -9608,9 +9705,9 @@ namespace OpenTween
                     {
                         if (configBrowserPath.StartsWith("\"", StringComparison.Ordinal) && configBrowserPath.Length > 2 && configBrowserPath.IndexOf("\"", 2, StringComparison.Ordinal) > -1)
                         {
-                            int sep = configBrowserPath.IndexOf("\"", 2, StringComparison.Ordinal);
-                            string browserPath = configBrowserPath.Substring(1, sep - 1);
-                            string arg = "";
+                            var sep = configBrowserPath.IndexOf("\"", 2, StringComparison.Ordinal);
+                            var browserPath = configBrowserPath.Substring(1, sep - 1);
+                            var arg = "";
                             if (sep < configBrowserPath.Length - 1)
                             {
                                 arg = configBrowserPath.Substring(sep + 1);
@@ -9654,7 +9751,7 @@ namespace OpenTween
             }
             else
             {
-                for (int i = 0; i < listView.Columns.Count; i++)
+                for (var i = 0; i < listView.Columns.Count; i++)
                 {
                     listView.Columns[i].Text = ColumnText[i];
                 }
@@ -9667,8 +9764,8 @@ namespace OpenTween
         private void SelectListItem(DetailsListView LView, int Index)
         {
             //単一
-            Rectangle bnd = new Rectangle();
-            bool flg = false;
+            var bnd = new Rectangle();
+            var flg = false;
             var item = LView.FocusedItem;
             if (item != null)
             {
@@ -9688,11 +9785,11 @@ namespace OpenTween
             if (flg) LView.Invalidate(bnd);
         }
 
-        private void SelectListItem(DetailsListView LView , int[] Index, int focusedIndex, int selectionMarkIndex)
+        private void SelectListItem(DetailsListView LView , int[]? Index, int focusedIndex, int selectionMarkIndex)
         {
             //複数
-            Rectangle bnd = new Rectangle();
-            bool flg = false;
+            var bnd = new Rectangle();
+            var flg = false;
             var item = LView.FocusedItem;
             if (item != null)
             {
@@ -9803,7 +9900,7 @@ namespace OpenTween
                 if (MyCommon.TwitterApiInfo.AccessLevel == TwitterApiAccessLevel.ReadWrite)
                 {
                     MessageBox.Show(Properties.Resources.ReAuthorizeText);
-                    SettingStripMenuItem_Click(null, null);
+                    SettingStripMenuItem_Click(this.SettingStripMenuItem, EventArgs.Empty);
                 }
 
                 // 取得失敗の場合は再試行する
@@ -9862,7 +9959,7 @@ namespace OpenTween
                 }
                 else if (selectedPosts.Length > 1)
                 {
-                    string QuestionText = Properties.Resources.RetweetQuestion2;
+                    var QuestionText = Properties.Resources.RetweetQuestion2;
                     if (_DoFavRetweetFlags) QuestionText = Properties.Resources.FavoriteRetweetQuestionText1;
                     switch (MessageBox.Show(QuestionText, "Retweet", MessageBoxButtons.YesNoCancel, MessageBoxIcon.Question))
                     {
@@ -9876,7 +9973,7 @@ namespace OpenTween
                 {
                     if (!SettingManager.Common.RetweetNoConfirm)
                     {
-                        string Questiontext = Properties.Resources.RetweetQuestion1;
+                        var Questiontext = Properties.Resources.RetweetQuestion1;
                         if (_DoFavRetweetFlags) Questiontext = Properties.Resources.FavoritesRetweetQuestionText2;
                         if (isConfirm && MessageBox.Show(Questiontext, "Retweet", MessageBoxButtons.OKCancel, MessageBoxIcon.Question) == DialogResult.Cancel)
                         {
@@ -9916,7 +10013,7 @@ namespace OpenTween
         private async Task FavoritesRetweetUnofficial()
         {
             var post = this.CurrentPost;
-            if (this.ExistCurrentPost && !post.IsDm)
+            if (this.ExistCurrentPost && post != null && !post.IsDm)
             {
                 _DoFavRetweetFlags = true;
                 var favoriteTask = this.FavoriteChange(true);
@@ -10034,7 +10131,7 @@ namespace OpenTween
         {
             if (string.IsNullOrEmpty(_rclickTabName)) return;
 
-            TabRename(_rclickTabName, out var _);
+            _ = TabRename(_rclickTabName, out _);
         }
 
         private async void BitlyToolStripMenuItem_Click(object sender, EventArgs e)
@@ -10045,7 +10142,7 @@ namespace OpenTween
 
         private async void ApiUsageInfoMenuItem_Click(object sender, EventArgs e)
         {
-            TwitterApiStatus apiStatus;
+            TwitterApiStatus? apiStatus;
 
             using (var dialog = new WaitingDialog(Properties.Resources.ApiInfo6))
             {
@@ -10071,10 +10168,8 @@ namespace OpenTween
                 }
             }
 
-            using (var apiDlg = new ApiInfoDialog())
-            {
-                apiDlg.ShowDialog(this);
-            }
+            using var apiDlg = new ApiInfoDialog();
+            apiDlg.ShowDialog(this);
         }
 
         private async void FollowCommandMenuItem_Click(object sender, EventArgs e)
@@ -10128,19 +10223,17 @@ namespace OpenTween
         {
             if (!skipInput)
             {
-                using (var inputName = new InputTabName())
-                {
-                    inputName.FormTitle = "Unfollow";
-                    inputName.FormDescription = Properties.Resources.FRMessage1;
-                    inputName.TabName = id;
+                using var inputName = new InputTabName();
+                inputName.FormTitle = "Unfollow";
+                inputName.FormDescription = Properties.Resources.FRMessage1;
+                inputName.TabName = id;
 
-                    if (inputName.ShowDialog(this) != DialogResult.OK)
-                        return;
-                    if (string.IsNullOrWhiteSpace(inputName.TabName))
-                        return;
+                if (inputName.ShowDialog(this) != DialogResult.OK)
+                    return;
+                if (string.IsNullOrWhiteSpace(inputName.TabName))
+                    return;
 
-                    id = inputName.TabName.Trim();
-                }
+                id = inputName.TabName.Trim();
             }
 
             using (var dialog = new WaitingDialog(Properties.Resources.RemoveCommandText1))
@@ -10208,7 +10301,7 @@ namespace OpenTween
                     return;
             }
 
-            string result = "";
+            string result;
             if (isFollowing)
             {
                 result = Properties.Resources.GetFriendshipInfo1 + System.Environment.NewLine;
@@ -10231,7 +10324,7 @@ namespace OpenTween
 
         internal async Task ShowFriendship(string[] ids)
         {
-            foreach (string id in ids)
+            foreach (var id in ids)
             {
                 bool isFollowing, isFollowed;
 
@@ -10258,8 +10351,8 @@ namespace OpenTween
                         return;
                 }
 
-                string result = "";
-                string ff = "";
+                var result = "";
+                var ff = "";
 
                 ff = "  ";
                 if (isFollowing)
@@ -10315,9 +10408,9 @@ namespace OpenTween
 
         private void doQuoteOfficial()
         {
-            if (this.ExistCurrentPost)
+            var post = this.CurrentPost;
+            if (this.ExistCurrentPost && post != null)
             {
-                var post = this.CurrentPost;
                 if (post.IsDm || !StatusText.Enabled)
                     return;
 
@@ -10341,9 +10434,9 @@ namespace OpenTween
         private void doReTweetUnofficial()
         {
             //RT @id:内容
-            if (this.ExistCurrentPost)
+            var post = this.CurrentPost;
+            if (this.ExistCurrentPost && post != null)
             {
-                var post = this.CurrentPost;
                 if (post.IsDm || !StatusText.Enabled)
                     return;
 
@@ -10352,7 +10445,7 @@ namespace OpenTween
                     MessageBox.Show("Protected.");
                     return;
                 }
-                string rtdata = post.Text;
+                var rtdata = post.Text;
                 rtdata = CreateRetweetUnofficial(rtdata, this.StatusText.Multiline);
 
                 var selection = (this.StatusText.SelectionStart, this.StatusText.SelectionLength);
@@ -10375,18 +10468,18 @@ namespace OpenTween
         private async void SearchButton_Click(object sender, EventArgs e)
         {
             //公式検索
-            Control pnl = ((Control)sender).Parent;
+            var pnl = ((Control)sender).Parent;
             if (pnl == null) return;
-            string tbName = pnl.Parent.Text;
+            var tbName = pnl.Parent.Text;
             var tb = (PublicSearchTabModel)_statuses.Tabs[tbName];
-            ComboBox cmb = (ComboBox)pnl.Controls["comboSearch"];
-            ComboBox cmbLang = (ComboBox)pnl.Controls["comboLang"];
+            var cmb = (ComboBox)pnl.Controls["comboSearch"];
+            var cmbLang = (ComboBox)pnl.Controls["comboLang"];
             cmb.Text = cmb.Text.Trim();
             // 検索式演算子 OR についてのみ大文字しか認識しないので強制的に大文字とする
-            bool Quote = false;
-            StringBuilder buf = new StringBuilder();
-            char[] c = cmb.Text.ToCharArray();
-            for (int cnt = 0; cnt < cmb.Text.Length; cnt++)
+            var Quote = false;
+            var buf = new StringBuilder();
+            var c = cmb.Text.ToCharArray();
+            for (var cnt = 0; cnt < cmb.Text.Length; cnt++)
             {
                 if (cnt > cmb.Text.Length - 4)
                 {
@@ -10424,7 +10517,7 @@ namespace OpenTween
             }
             if (queryChanged)
             {
-                int idx = cmb.Items.IndexOf(tb.SearchWords);
+                var idx = cmb.Items.IndexOf(tb.SearchWords);
                 if (idx > -1) cmb.Items.RemoveAt(idx);
                 cmb.Items.Insert(0, tb.SearchWords);
                 cmb.Text = tb.SearchWords;
@@ -10460,9 +10553,9 @@ namespace OpenTween
             }
             else
             {
-                DetailsListView listView = null;
+                DetailsListView? listView;
 
-                TabModel tb = _statuses.RemovedTab.Pop();
+                var tb = _statuses.RemovedTab.Pop();
                 if (tb.TabType == MyCommon.TabUsageType.Related)
                 {
                     var relatedTab = _statuses.GetTabByType(MyCommon.TabUsageType.Related);
@@ -10482,10 +10575,11 @@ namespace OpenTween
                     else
                     {
                         const string TabName = "Related Tweets";
-                        string renamed = TabName;
-                        for (int i = 2; i <= 100; i++)
+                        var renamed = TabName;
+                        for (var i = 2; i <= 100; i++)
                         {
-                            if (!_statuses.ContainsTab(renamed)) break;
+                            if (!_statuses.ContainsTab(renamed))
+                                break;
                             renamed = TabName + i;
                         }
                         tb.TabName = renamed;
@@ -10502,10 +10596,11 @@ namespace OpenTween
                 }
                 else
                 {
-                    string renamed = tb.TabName;
-                    for (int i = 1; i < int.MaxValue; i++)
+                    var renamed = tb.TabName;
+                    for (var i = 1; i < int.MaxValue; i++)
                     {
-                        if (!_statuses.ContainsTab(renamed)) break;
+                        if (!_statuses.ContainsTab(renamed))
+                            break;
                         renamed = tb.TabName + "(" + i + ")";
                     }
                     tb.TabName = renamed;
@@ -10550,15 +10645,13 @@ namespace OpenTween
 
         public void ListManageUserContext(string screenName)
         {
-            using (var listSelectForm = new MyLists(screenName, this.twitterApi))
-            {
-                listSelectForm.ShowDialog(this);
-            }
+            using var listSelectForm = new MyLists(screenName, this.twitterApi);
+            listSelectForm.ShowDialog(this);
         }
 
         private void SearchControls_Enter(object sender, EventArgs e)
         {
-            Control pnl = (Control)sender;
+            var pnl = (Control)sender;
             foreach (Control ctl in pnl.Controls)
             {
                 ctl.TabStop = true;
@@ -10567,7 +10660,7 @@ namespace OpenTween
 
         private void SearchControls_Leave(object sender, EventArgs e)
         {
-            Control pnl = (Control)sender;
+            var pnl = (Control)sender;
             foreach (Control ctl in pnl.Controls)
             {
                 ctl.TabStop = false;
@@ -10586,7 +10679,7 @@ namespace OpenTween
 
         private void HashManageMenuItem_Click(object sender, EventArgs e)
         {
-            DialogResult rslt = DialogResult.Cancel;
+            DialogResult rslt;
             try
             {
                 rslt = HashMgr.ShowDialog();
@@ -10624,7 +10717,7 @@ namespace OpenTween
             //    StatusText.Focus();
             //}
             this.MarkSettingCommonModified();
-            this.StatusText_TextChanged(null, null);
+            this.StatusText_TextChanged(this.StatusText, EventArgs.Empty);
         }
 
         private void HashToggleMenuItem_Click(object sender, EventArgs e)
@@ -10643,11 +10736,11 @@ namespace OpenTween
                 HashTogglePullDownMenuItem.Checked = false;
             }
             this.MarkSettingCommonModified();
-            this.StatusText_TextChanged(null, null);
+            this.StatusText_TextChanged(this.StatusText, EventArgs.Empty);
         }
 
         private void HashStripSplitButton_ButtonClick(object sender, EventArgs e)
-            => this.HashToggleMenuItem_Click(null, null);
+            => this.HashToggleMenuItem_Click(this.HashToggleMenuItem, EventArgs.Empty);
 
         public void SetPermanentHashtag(string hashtag)
         {
@@ -10694,7 +10787,7 @@ namespace OpenTween
 
             var tab = this.CurrentTab;
             var post = this.CurrentPost;
-            if (tab.TabType == MyCommon.TabUsageType.DirectMessage || !this.ExistCurrentPost || post.IsDm)
+            if (tab.TabType == MyCommon.TabUsageType.DirectMessage || !this.ExistCurrentPost || post == null || post.IsDm)
             {
                 this.FavOpMenuItem.Enabled = false;
                 this.UnFavOpMenuItem.Enabled = false;
@@ -10739,7 +10832,7 @@ namespace OpenTween
             {
                 this.RefreshPrevOpMenuItem.Enabled = false;
             }
-            if (!this.ExistCurrentPost || post.InReplyToStatusId == null)
+            if (!this.ExistCurrentPost || post == null || post.InReplyToStatusId == null)
             {
                 OpenRepSourceOpMenuItem.Enabled = false;
             }
@@ -10747,7 +10840,7 @@ namespace OpenTween
             {
                 OpenRepSourceOpMenuItem.Enabled = true;
             }
-            if (!this.ExistCurrentPost || string.IsNullOrEmpty(post.RetweetedBy))
+            if (!this.ExistCurrentPost || post == null || string.IsNullOrEmpty(post.RetweetedBy))
             {
                 OpenRterHomeMenuItem.Enabled = false;
             }
@@ -10756,14 +10849,14 @@ namespace OpenTween
                 OpenRterHomeMenuItem.Enabled = true;
             }
 
-            if (this.ExistCurrentPost)
+            if (this.ExistCurrentPost && post != null)
             {
                 this.DelOpMenuItem.Enabled = post.CanDeleteBy(this.tw.UserId);
             }
         }
 
         private void MenuItemTab_DropDownOpening(object sender, EventArgs e)
-            => this.ContextMenuTabProperty_Opening(sender, null);
+            => this.ContextMenuTabProperty_Opening(sender, null!);
 
         public Twitter TwitterInstance
             => this.tw;
@@ -10809,7 +10902,8 @@ namespace OpenTween
             else
                 PublicSearchQueryMenuItem.Enabled = false;
 
-            if (!this.ExistCurrentPost)
+            var post = this.CurrentPost;
+            if (!this.ExistCurrentPost || post == null)
             {
                 this.CopySTOTMenuItem.Enabled = false;
                 this.CopyURLMenuItem.Enabled = false;
@@ -10821,7 +10915,6 @@ namespace OpenTween
                 this.CopyURLMenuItem.Enabled = true;
                 this.CopyUserIdStripMenuItem.Enabled = true;
 
-                var post = this.CurrentPost;
                 if (post.IsDm) this.CopyURLMenuItem.Enabled = false;
                 if (post.IsProtect) this.CopySTOTMenuItem.Enabled = false;
             }
@@ -10835,23 +10928,21 @@ namespace OpenTween
 
         private async Task doShowUserStatus(string id, bool ShowInputDialog)
         {
-            TwitterUser user = null;
+            TwitterUser? user = null;
 
             if (ShowInputDialog)
             {
-                using (var inputName = new InputTabName())
-                {
-                    inputName.FormTitle = "Show UserStatus";
-                    inputName.FormDescription = Properties.Resources.FRMessage1;
-                    inputName.TabName = id;
+                using var inputName = new InputTabName();
+                inputName.FormTitle = "Show UserStatus";
+                inputName.FormDescription = Properties.Resources.FRMessage1;
+                inputName.TabName = id;
 
-                    if (inputName.ShowDialog(this) != DialogResult.OK)
-                        return;
-                    if (string.IsNullOrWhiteSpace(inputName.TabName))
-                        return;
+                if (inputName.ShowDialog(this) != DialogResult.OK)
+                    return;
+                if (string.IsNullOrWhiteSpace(inputName.TabName))
+                    return;
 
-                    id = inputName.TabName.Trim();
-                }
+                id = inputName.TabName.Trim();
             }
 
             using (var dialog = new WaitingDialog(Properties.Resources.doShowUserStatusText1))
@@ -10879,17 +10970,15 @@ namespace OpenTween
 
         private async Task doShowUserStatus(TwitterUser user)
         {
-            using (var userDialog = new UserInfoDialog(this, this.twitterApi))
-            {
-                var showUserTask = userDialog.ShowUserAsync(user);
-                userDialog.ShowDialog(this);
+            using var userDialog = new UserInfoDialog(this, this.twitterApi);
+            var showUserTask = userDialog.ShowUserAsync(user);
+            userDialog.ShowDialog(this);
 
-                this.Activate();
-                this.BringToFront();
+            this.Activate();
+            this.BringToFront();
 
-                // ユーザー情報の表示が完了するまで userDialog を破棄しない
-                await showUserTask;
-            }
+            // ユーザー情報の表示が完了するまで userDialog を破棄しない
+            await showUserTask;
         }
 
         internal Task ShowUserStatus(string id, bool ShowInputDialog)
@@ -10909,10 +10998,10 @@ namespace OpenTween
 
         private async void RtCountMenuItem_Click(object sender, EventArgs e)
         {
-            if (!this.ExistCurrentPost)
+            var post = this.CurrentPost;
+            if (!this.ExistCurrentPost || post == null)
                 return;
 
-            var post = this.CurrentPost;
             var statusId = post.RetweetedId ?? post.StatusId;
             TwitterStatus status;
 
@@ -10939,7 +11028,7 @@ namespace OpenTween
             MessageBox.Show(status.RetweetCount + Properties.Resources.RtCountText1);
         }
 
-        private HookGlobalHotkey _hookGlobalHotkey;
+        private readonly HookGlobalHotkey _hookGlobalHotkey;
         public TweenMain()
         {
             _hookGlobalHotkey = new HookGlobalHotkey(this);
@@ -11044,12 +11133,12 @@ namespace OpenTween
             if (ImageSelector.Visible)
             {
                 this.MarkSettingCommonModified();
-                this.StatusText_TextChanged(null, null);
+                this.StatusText_TextChanged(this.StatusText, EventArgs.Empty);
             }
         }
 
         private void ImageSelector_VisibleChanged(object sender, EventArgs e)
-            => this.StatusText_TextChanged(null, null);
+            => this.StatusText_TextChanged(this.StatusText, EventArgs.Empty);
 
         /// <summary>
         /// StatusTextでCtrl+Vが押下された時の処理
@@ -11074,10 +11163,8 @@ namespace OpenTween
                                    == DialogResult.OK)
                     {
                         // clipboardから画像を取得
-                        using (var image = Clipboard.GetImage())
-                        {
-                            this.ImageSelector.BeginSelection(image);
-                        }
+                        using var image = Clipboard.GetImage();
+                        this.ImageSelector.BeginSelection(image);
                     }
                 }
             }
@@ -11090,10 +11177,8 @@ namespace OpenTween
 
         private void ListManageToolStripMenuItem_Click(object sender, EventArgs e)
         {
-            using (ListManage form = new ListManage(tw))
-            {
-                form.ShowDialog(this);
-            }
+            using var form = new ListManage(tw);
+            form.ShowDialog(this);
         }
 
         private bool ModifySettingCommon { get; set; }
@@ -11103,7 +11188,7 @@ namespace OpenTween
         private void MenuItemCommand_DropDownOpening(object sender, EventArgs e)
         {
             var post = this.CurrentPost;
-            if (this.ExistCurrentPost && !post.IsDm)
+            if (this.ExistCurrentPost && post != null && !post.IsDm)
                 RtCountMenuItem.Enabled = true;
             else
                 RtCountMenuItem.Enabled = false;
@@ -11135,7 +11220,7 @@ namespace OpenTween
         private async void ShowRelatedStatusesMenuItem_Click(object sender, EventArgs e)
         {
             var post = this.CurrentPost;
-            if (this.ExistCurrentPost && !post.IsDm)
+            if (this.ExistCurrentPost && post != null && !post.IsDm)
             {
                 try
                 {
@@ -11221,7 +11306,7 @@ namespace OpenTween
 
         private void CacheInfoMenuItem_Click(object sender, EventArgs e)
         {
-            StringBuilder buf = new StringBuilder();
+            var buf = new StringBuilder();
             //buf.AppendFormat("キャッシュメモリ容量         : {0}bytes({1}MB)" + Environment.NewLine, IconCache.CacheMemoryLimit, ((ImageDictionary)IconCache).CacheMemoryLimit / 1048576);
             //buf.AppendFormat("物理メモリ使用割合           : {0}%" + Environment.NewLine, IconCache.PhysicalMemoryLimit);
             buf.AppendFormat("キャッシュエントリ保持数     : {0}" + Environment.NewLine, IconCache.CacheCount);
@@ -11371,7 +11456,7 @@ namespace OpenTween
                 }
                 if (ev.Event == "unfavorite" && ev.Username.Equals(tw.Username, StringComparison.InvariantCultureIgnoreCase))
                 {
-                    var favTab = this._statuses.GetTabByType(MyCommon.TabUsageType.Favorites);
+                    var favTab = this._statuses.FavoriteTab;
                     favTab.EnqueueRemovePost(ev.Id, setIsDeleted: false);
                 }
             }
@@ -11385,7 +11470,7 @@ namespace OpenTween
                 NotifyIcon1.BalloonTipIcon = ToolTipIcon.Info;
                 //if (SettingDialog.DispUsername) NotifyIcon1.BalloonTipTitle = tw.Username + " - "; else NotifyIcon1.BalloonTipTitle = "";
                 //NotifyIcon1.BalloonTipTitle += Application.ProductName + " [" + ev.Event.ToUpper() + "] by " + ((string)(!string.IsNullOrEmpty(ev.Username) ? ev.Username : ""), string);
-                StringBuilder title = new StringBuilder();
+                var title = new StringBuilder();
                 if (SettingManager.Common.DispUsername)
                 {
                     title.Append(tw.Username);
@@ -11434,22 +11519,20 @@ namespace OpenTween
             }
 
             //サウンド再生
-            string snd = SettingManager.Common.EventSoundFile;
+            var snd = SettingManager.Common.EventSoundFile;
             if (!_initial && SettingManager.Common.PlaySound && !string.IsNullOrEmpty(snd))
             {
                 if ((ev.Eventtype & SettingManager.Common.EventNotifyFlag) != 0 && IsMyEventNotityAsEventType(ev))
                 {
                     try
                     {
-                        string dir = Application.StartupPath;
+                        var dir = Application.StartupPath;
                         if (Directory.Exists(Path.Combine(dir, "Sounds")))
                         {
                             dir = Path.Combine(dir, "Sounds");
                         }
-                        using (SoundPlayer player = new SoundPlayer(Path.Combine(dir, snd)))
-                        {
-                            player.Play();
-                        }
+                        using var player = new SoundPlayer(Path.Combine(dir, snd));
+                        player.Play();
                     }
                     catch (Exception)
                     {
@@ -11482,7 +11565,7 @@ namespace OpenTween
         {
             if (TrackToolStripMenuItem.Checked)
             {
-                using (InputTabName inputForm = new InputTabName())
+                using (var inputForm = new InputTabName())
                 {
                     inputForm.TabName = inputTrack;
                     inputForm.FormTitle = "Input track word";
@@ -11579,27 +11662,26 @@ namespace OpenTween
         {
             var id = this.CurrentPost?.ScreenName ?? "";
 
-            using (InputTabName inputName = new InputTabName())
+            using var inputName = new InputTabName();
+            inputName.FormTitle = caption;
+            inputName.FormDescription = Properties.Resources.FRMessage1;
+            inputName.TabName = id;
+
+            if (inputName.ShowDialog() == DialogResult.OK &&
+                !string.IsNullOrEmpty(inputName.TabName.Trim()))
             {
-                inputName.FormTitle = caption;
-                inputName.FormDescription = Properties.Resources.FRMessage1;
-                inputName.TabName = id;
-                if (inputName.ShowDialog() == DialogResult.OK &&
-                    !string.IsNullOrEmpty(inputName.TabName.Trim()))
-                {
-                    id = inputName.TabName.Trim();
-                }
-                else
-                {
-                    id = "";
-                }
+                id = inputName.TabName.Trim();
+            }
+            else
+            {
+                id = "";
             }
             return id;
         }
 
         private async void UserTimelineToolStripMenuItem_Click(object sender, EventArgs e)
         {
-            string id = GetUserIdFromCurPostOrInput("Show UserTimeline");
+            var id = GetUserIdFromCurPostOrInput("Show UserTimeline");
             if (!string.IsNullOrEmpty(id))
             {
                 await this.AddNewTabForUserTimeline(id);
@@ -11655,7 +11737,7 @@ namespace OpenTween
                     var post = this.CurrentPost;
                     if (post != null)
                     {
-                        string xUrl = SettingManager.Common.UserAppointUrl;
+                        var xUrl = SettingManager.Common.UserAppointUrl;
                         xUrl = xUrl.Replace("{ID}", post.ScreenName);
 
                         var statusId = post.RetweetedId ?? post.StatusId;
@@ -11725,7 +11807,7 @@ namespace OpenTween
         {
             if (e.KeyCode == Keys.Space)
             {
-                this.JumpUnreadMenuItem_Click(null, null);
+                this.JumpUnreadMenuItem_Click(this.JumpUnreadMenuItem, EventArgs.Empty);
 
                 e.SuppressKeyPress = true;
             }