Track offset of center child view in Gallery for later layouts

When apps request layouts while scrolling is in progress, Gallery
children can get offset in strange ways. Compensate for this by
tracking the last known offset and applying it during layout.

Bug 7245853

Change-Id: I9d746ae6bb06918e2d920c58052f72e749a7ffbf

diff --git a/core/java/android/widget/Gallery.java b/core/java/android/widget/Gallery.java
index b72b8cb..e0c5bbd 100644 (file)
--- a/core/java/android/widget/Gallery.java
+++ b/core/java/android/widget/Gallery.java
@@ -182,6 +182,12 @@ public class Gallery extends AbsSpinner implements GestureDetector.OnGestureList
      */
     private boolean mIsRtl = true;
     
+    /**
+     * Offset between the center of the selected child view and the center of the Gallery.
+     * Used to reset position correctly during layout.
+     */
+    private int mSelectedCenterOffset;
+
     public Gallery(Context context) {
         this(context, null);
     }
@@ -395,6 +401,14 @@ public class Gallery extends AbsSpinner implements GestureDetector.OnGestureList
         
         setSelectionToCenterChild();
 
+        final View selChild = mSelectedChild;
+        if (selChild != null) {
+            final int childLeft = selChild.getLeft();
+            final int childCenter = selChild.getWidth() / 2;
+            final int galleryCenter = getWidth() / 2;
+            mSelectedCenterOffset = childLeft + childCenter - galleryCenter;
+        }
+
         onScrollChanged(0, 0, 0, 0); // dummy values, View's implementation does not use these.
 
         invalidate();
@@ -537,6 +551,7 @@ public class Gallery extends AbsSpinner implements GestureDetector.OnGestureList
             // We haven't been callbacking during the fling, so do it now
             super.selectionChanged();
         }
+        mSelectedCenterOffset = 0;
         invalidate();
     }
     
@@ -650,7 +665,8 @@ public class Gallery extends AbsSpinner implements GestureDetector.OnGestureList
         View sel = makeAndAddView(mSelectedPosition, 0, 0, true);
         
         // Put the selected child in the center
-        int selectedOffset = childrenLeft + (childrenWidth / 2) - (sel.getWidth() / 2);
+        int selectedOffset = childrenLeft + (childrenWidth / 2) - (sel.getWidth() / 2) +
+                mSelectedCenterOffset;
         sel.offsetLeftAndRight(selectedOffset);
 
         fillToGalleryRight();