From 1c1945569fd2a40dfdec09bdcb9c0ec0706b026f Mon Sep 17 00:00:00 2001
From: Xin Chen <xch@fb.com>
Date: Mon, 6 Dec 2021 09:39:08 -0800
Subject: [PATCH] Fix mis-use of the post animated value when predict fling
 distance

Summary:
This diff fixes an edge case where scroll to the end of the list may trigger a bounce back effect.

This issue is a regression from D32487846 (https://github.com/facebook/react-native/commit/f70018b37532622f08f20b2c51cdbfca55d730ea) (See [this comment](https://www.internalfb.com/diff/D32487846 (https://github.com/facebook/react-native/commit/f70018b37532622f08f20b2c51cdbfca55d730ea)?dst_version_fbid=263960175698224&transaction_fbid=566201141113715)) that zero velocity fling at the end of the scroll view makes the next fling animator use previous post animation position. This is due to cached `postAnimationValue` is applied mistakenly.

- Pass velocity instead of velocity sign to the helper class
- Update helper class logic to decide if we need to use post animated value from last fling animation

Changelog:
[Internal]

Reviewed By: javache

Differential Revision: D32566010

fbshipit-source-id: 1c61659030151f8f2c7648ca901b8b4158835538
---
 .../react/views/scroll/ReactHorizontalScrollView.java         | 4 ++--
 .../java/com/facebook/react/views/scroll/ReactScrollView.java | 4 ++--
 .../facebook/react/views/scroll/ReactScrollViewHelper.java    | 4 ++--
 3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactHorizontalScrollView.java b/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactHorizontalScrollView.java
index ae5443e098b..dcc64670f7c 100644
--- a/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactHorizontalScrollView.java
+++ b/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactHorizontalScrollView.java
@@ -816,7 +816,7 @@ public class ReactHorizontalScrollView extends HorizontalScrollView
             this,
             getScrollX(),
             getReactScrollViewScrollState().getFinalAnimatedPositionScroll().x,
-            velocityX > 0), // startX
+            velocityX), // startX
         getScrollY(), // startY
         velocityX, // velocityX
         0, // velocityY
@@ -847,7 +847,7 @@ public class ReactHorizontalScrollView extends HorizontalScrollView
                 this,
                 getScrollX(),
                 getReactScrollViewScrollState().getFinalAnimatedPositionScroll().x,
-                velocity > 0));
+                velocity));
     double targetOffset = (double) predictFinalScrollPosition(velocity);
 
     int previousPage = (int) Math.floor(currentOffset / interval);
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
index a73db8746f2..755f54420c0 100644
--- a/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollView.java
+++ b/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollView.java
@@ -606,7 +606,7 @@ public class ReactScrollView extends ScrollView
             this,
             getScrollY(),
             getReactScrollViewScrollState().getFinalAnimatedPositionScroll().y,
-            velocityY > 0), // startY
+            velocityY), // startY
         0, // velocityX
         velocityY, // velocityY
         0, // minX
@@ -636,7 +636,7 @@ public class ReactScrollView extends ScrollView
                 this,
                 getScrollY(),
                 getReactScrollViewScrollState().getFinalAnimatedPositionScroll().y,
-                velocity > 0));
+                velocity));
     double targetOffset = (double) predictFinalScrollPosition(velocity);
 
     int previousPage = (int) Math.floor(currentOffset / interval);
diff --git a/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollViewHelper.java b/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollViewHelper.java
index 018a719084e..6d76c670452 100644
--- a/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollViewHelper.java
+++ b/ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactScrollViewHelper.java
@@ -339,9 +339,9 @@ public class ReactScrollViewHelper {
           final T scrollView,
           final int currentValue,
           final int postAnimationValue,
-          final boolean isPositiveVelocity) {
+          final int velocity) {
     final ReactScrollViewScrollState scrollState = scrollView.getReactScrollViewScrollState();
-    final int velocityDirectionMask = isPositiveVelocity ? 1 : -1;
+    final int velocityDirectionMask = velocity != 0 ? velocity / Math.abs(velocity) : 0;
     final boolean isMovingTowardsAnimatedValue =
         velocityDirectionMask * (postAnimationValue - currentValue) > 0;