From 87ad1e857096393fcb7b4b086a117d08e1c4f7d5 Mon Sep 17 00:00:00 2001
From: Xin Chen <xch@fb.com>
Date: Fri, 4 Mar 2022 15:50:00 -0800
Subject: [PATCH] Intercept touch event for simulated joystick scrolling to
 avoid nested scroll view issues

Summary:
The issue to be fixed here is an edge case when in nested scroll view, for example vertical scroll wraps horizontal scroll, when user scrolls horizontally then move the joystick downwards, the horizontal scroll would bounce back. This is shown in the demo:

https://pxl.cl/209f8

The root cause of the issue is due to two workflows fight to set the scroll position and confusing the scroll change dispatcher to calculate fling velocity direction, which caused a wrong fling behavior. Check this log and description to get more details:

{F706620839}

To fix the issue, in this diff we overridden the `onInterceptTouchEvent` method in panel app scroll views, and make it return true when the previous scroll is still running. This effectively skips the drag slop in the default scroll view behavior, as we know the touch event should've been handled by the scroll view if it's still scrolling.

This way, the vertical scroll part on the vertical scroll view will not be dispatched to the horizontal scroll at all. This allows the nested scroll view to work separately.

Changelog:
[Android][Internal] - Share the post intercept touch event logic in scroll views

Reviewed By: javache

Differential Revision: D34627329

fbshipit-source-id: d500ec3bfbe349a45ef5c1360b5c8807c168f682
---
 .../views/scroll/ReactHorizontalScrollView.java    | 14 +++++++++-----
 .../react/views/scroll/ReactScrollView.java        | 14 +++++++++-----
 2 files changed, 18 insertions(+), 10 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 1317c6e43de..006feb2ffac 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
@@ -460,11 +460,7 @@ public class ReactHorizontalScrollView extends HorizontalScrollView
 
     try {
       if (super.onInterceptTouchEvent(ev)) {
-        NativeGestureUtil.notifyNativeGestureStarted(this, ev);
-        ReactScrollViewHelper.emitScrollBeginDragEvent(this);
-        mDragging = true;
-        enableFpsListener();
-        getFlingAnimator().cancel();
+        handleInterceptedTouchEvent(ev);
         return true;
       }
     } catch (IllegalArgumentException e) {
@@ -477,6 +473,14 @@ public class ReactHorizontalScrollView extends HorizontalScrollView
     return false;
   }
 
+  protected void handleInterceptedTouchEvent(MotionEvent ev) {
+    NativeGestureUtil.notifyNativeGestureStarted(this, ev);
+    ReactScrollViewHelper.emitScrollBeginDragEvent(this);
+    mDragging = true;
+    enableFpsListener();
+    getFlingAnimator().cancel();
+  }
+
   @Override
   public boolean pageScroll(int direction) {
     boolean handled = super.pageScroll(direction);
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 3fbfb7a4d52..32261eb3dc9 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
@@ -340,11 +340,7 @@ public class ReactScrollView extends ScrollView
 
     try {
       if (super.onInterceptTouchEvent(ev)) {
-        NativeGestureUtil.notifyNativeGestureStarted(this, ev);
-        ReactScrollViewHelper.emitScrollBeginDragEvent(this);
-        mDragging = true;
-        enableFpsListener();
-        getFlingAnimator().cancel();
+        handleInterceptedTouchEvent(ev);
         return true;
       }
     } catch (IllegalArgumentException e) {
@@ -357,6 +353,14 @@ public class ReactScrollView extends ScrollView
     return false;
   }
 
+  protected void handleInterceptedTouchEvent(MotionEvent ev) {
+    NativeGestureUtil.notifyNativeGestureStarted(this, ev);
+    ReactScrollViewHelper.emitScrollBeginDragEvent(this);
+    mDragging = true;
+    enableFpsListener();
+    getFlingAnimator().cancel();
+  }
+
   @Override
   public boolean onTouchEvent(MotionEvent ev) {
     if (!mScrollEnabled) {