Fix incorrect platform auto-scroll to right when height changes

Summary:
When the height of a HorizontalScrollView changes and there is a `layout` event, it can cause the underlying platform View code to scroll slightly to the right.

I'm... not really sure why, even after looking at the View code for a while. But it is clearly detectable and mirrors issues with RTL that were fixed recently.

This might warrant more investigation, but I believe the fix is relatively safe - we detect if there's an autoscroll only if the height changes and only if the scroll happens in "layout". That scopes the hack pretty well to just this bug.

There aren't really times when we actually want layout to scroll to the right, so... I think this is reasonable.

Changelog: [Changed][Android] Fixed issue that causes HorizontalScrollView to shift to the right when a TextInput is selected and keyboard pops up

Reviewed By: mdvacca

Differential Revision: D26972710

fbshipit-source-id: 441b1a3f07b9b68195a9e5e9a0c8d75c9d24a109

ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactHorizontalScrollView.java

@@ -54,12 +54,16 @@ public class ReactHorizontalScrollView extends HorizontalScrollView
   private static boolean DEBUG_MODE = false && ReactBuildConfig.DEBUG;
   private static String TAG = ReactHorizontalScrollView.class.getSimpleName();
 
+  private static int NO_SCROLL_POSITION = Integer.MIN_VALUE;
+
   private static @Nullable Field sScrollerField;
   private static boolean sTriedToGetScrollerField = false;
   private static final String CONTENT_OFFSET_LEFT = "contentOffsetLeft";
   private static final String CONTENT_OFFSET_TOP = "contentOffsetTop";
   private int mLayoutDirection;
 
+  private int mScrollXAfterMeasure = NO_SCROLL_POSITION;
+
   private static final int UNSET_CONTENT_OFFSET = -1;
 
   private final OnScrollDispatchHelper mOnScrollDispatchHelper = new OnScrollDispatchHelper();
@@ -275,7 +279,15 @@ protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
           measuredHeight);
     }
 
+    boolean measuredHeightChanged = getMeasuredHeight() != measuredHeight;
+
     setMeasuredDimension(measuredWidth, measuredHeight);
+
+    // See how `mScrollXAfterMeasure` is used in `onLayout`, and why we only enable the
+    // hack if the height has changed.
+    if (measuredHeightChanged && mScroller != null) {
+      mScrollXAfterMeasure = mScroller.getCurrX();
+    }
   }
 
   @Override
@@ -284,6 +296,30 @@ protected void onLayout(boolean changed, int l, int t, int r, int b) {
       FLog.i(TAG, "onLayout[%d] l %d t %d r %d b %d", getId(), l, t, r, b);
     }
 
+    // Has the scrollX changed between the last onMeasure and this layout?
+    // If so, cancel the animation.
+    // Essentially, if the height changes (due to keyboard popping up, for instance) the
+    // underlying View.layout method will in some cases scroll to an incorrect X position -
+    // see also the hacks in `fling`. The order of layout is called in the order of: onMeasure,
+    // layout, onLayout.
+    // We cannot override `layout` but we can detect the sequence of events between onMeasure
+    // and onLayout.
+    if (mScrollXAfterMeasure != NO_SCROLL_POSITION
+        && mScroller != null
+        && mScrollXAfterMeasure != mScroller.getFinalX()
+        && !mScroller.isFinished()) {
+      if (DEBUG_MODE) {
+        FLog.i(
+            TAG,
+            "onLayout[%d] scroll hack enabled: reset to previous scrollX position of %d",
+            getId(),
+            mScrollXAfterMeasure);
+      }
+      mScroller.startScroll(mScrollXAfterMeasure, mScroller.getFinalY(), 0, 0);
+      mScroller.forceFinished(true);
+      mScrollXAfterMeasure = NO_SCROLL_POSITION;
+    }
+
     // Call with the present values in order to re-layout if necessary
     // If a "pending" value has been set, we restore that value.
     // That value gets cleared by reactScrollTo.