Workaround a wrong fling direction if FlatList or VirtualizedList is …

…inverted.
facebook · Sep 14, 2018 · 107a9ec · 107a9ec
1 parent a3752c6
commit 107a9ec
Showing 1 changed file with 10 additions and 0 deletions.
diff --git a/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollView.java b/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollView.java
@@ -302,6 +302,16 @@ public void getClippingRect(Rect outClippingRect) {
 
   @Override
   public void fling(int velocityY) {
+    // Workaround.
+    // On Android P if a ScrollView is inverted, we will get a wrong sign for
+    // velocityY (see https://issuetracker.google.com/issues/112385925). 
+    // At the same time, mOnScrollDispatchHelper tracks the correct velocity direction. 
+    //
+    // Hence, we can use the absolute value from whatever the OS gives
+    // us and use the sign of what mOnScrollDispatchHelper has tracked.
+    velocityY = (int)(Math.abs(velocityY) * Math.signum(mOnScrollDispatchHelper.getYFlingVelocity()));
+
+
     if (mPagingEnabled) {
       smoothScrollAndSnap(velocityY);
     } else if (mScroller != null) {