Fix home/back buttons flow in PreferenceActivity.

Bug: b/35977048
Test: Done manually. Automated test will be added later.

After recent changes in PreferenceActivity finishing the activity on
pressing back is not correct anymore. Instead onBackButton method should
be called to deal with it (we have fragments transactions for instance).

There can be multiple buttons:
1. The native default one - calls onBackPressed by default so no extra work
needed.
2. PreferenceActivity has buttons that can de displayed when settting
EXTRA_PREFS_SHOW_BUTTON_BAR to true. But it is a private API and I
didn't find any usage of it, so there is no need to change that. Also
it looks like something very specific used in WiFi wizards.
3. Apps often use a toolbar that has a home button which essentialy
emulates back button. The issue is that this Activity never had support
for this. So apps had to override onOptionsItemSelected and some of
those are unfortunately calling finish() which worked previously when
PreferenceActivity wasn't using fragments in single pane. This CL adds
support so app will no longer need to override that method and some
apps need to be instructed to use that override in O.

Change-Id: I94f557edb2e03f89fbf02e800beb390b2ad0544f

diff --git a/core/java/android/preference/PreferenceActivity.java b/core/java/android/preference/PreferenceActivity.java
index 600d82f..d59d9f7 100644 (file)
--- a/core/java/android/preference/PreferenceActivity.java
+++ b/core/java/android/preference/PreferenceActivity.java
@@ -40,6 +40,7 @@ import android.util.AttributeSet;
 import android.util.TypedValue;
 import android.util.Xml;
 import android.view.LayoutInflater;
+import android.view.MenuItem;
 import android.view.View;
 import android.view.View.OnClickListener;
 import android.view.ViewGroup;
@@ -75,12 +76,11 @@ import java.util.List;
  * however vary; currently there are two major approaches it may take:
  *
  * <ul>
- * <li>On a small screen it may display only the headers as a single list
- * when first launched.  Selecting one of the header items will re-launch
- * the activity with it only showing the PreferenceFragment of that header.
- * <li>On a large screen in may display both the headers and current
- * PreferenceFragment together as panes.  Selecting a header item switches
- * to showing the correct PreferenceFragment for that item.
+ * <li>On a small screen it may display only the headers as a single list when first launched.
+ * Selecting one of the header items will only show the PreferenceFragment of that header (on
+ * Android N and lower a new Activity is launched).
+ * <li>On a large screen in may display both the headers and current PreferenceFragment together as
+ * panes. Selecting a header item switches to showing the correct PreferenceFragment for that item.
  * </ul>
  *
  * <p>Subclasses of PreferenceActivity should implement
@@ -536,6 +536,16 @@ public abstract class PreferenceActivity extends ListActivity implements
     }
 
     @Override
+    public boolean onOptionsItemSelected(MenuItem item) {
+        if (item.getItemId() == android.R.id.home) {
+            // Override home navigation button to call onBackPressed (b/35152749).
+            onBackPressed();
+            return true;
+        }
+        return super.onOptionsItemSelected(item);
+    }
+
+    @Override
     protected void onCreate(@Nullable Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);