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Fix Inverted Horizontal ScrollView on Android #23233

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Fix Inverted Horizontal ScrollView on Android #23233

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18 changes: 14 additions & 4 deletions ReactAndroid/src/main/java/com/facebook/react/views/scroll/ReactHorizontalScrollView.java
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Original file line number Diff line number Diff line change
Expand Up @@ -286,8 +286,18 @@ public boolean onTouchEvent(MotionEvent ev) {

@Override
public void fling(int velocityX) {

// Workaround.
// On Android P if a ScrollView is inverted, we will get a wrong sign for
// velocityX (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.
final int correctedVelocityX = (int)(Math.abs(velocityX) * Math.signum(mOnScrollDispatchHelper.getXFlingVelocity()));

if (mPagingEnabled) {
flingAndSnap(velocityX);
flingAndSnap(correctedVelocityX);
} else if (mScroller != null) {
// FB SCROLLVIEW CHANGE

Expand All @@ -302,7 +312,7 @@ public void fling(int velocityX) {
mScroller.fling(
getScrollX(), // startX
getScrollY(), // startY
velocityX, // velocityX
correctedVelocityX, // velocityX
0, // velocityY
0, // minX
Integer.MAX_VALUE, // maxX
Expand All @@ -316,9 +326,9 @@ public void fling(int velocityX) {

// END FB SCROLLVIEW CHANGE
} else {
super.fling(velocityX);
super.fling(correctedVelocityX);
}
handlePostTouchScrolling(velocityX, 0);
handlePostTouchScrolling(correctedVelocityX, 0);
}

@Override
Expand Down