Xin Chen
f70018b375
Summary:
This diff fixes two edge case (similar to a race condition) that caused unexpected behaviors.
**Problem one**
{F680816408}
The previous fling animation is not canceled when user starts to scroll or drag. This is causing both the animation and scroll are setting the scroll position. Depends on the animation path and scroll speed, there may be cases where the [velocity calculation](https://fburl.com/code/010lsu72) ends up getting reversed values. See P467905091 as an example where you can see `mXFlingVelocity` goes back and forth from positive to negative.
It's hard to see if the wrong values are in the middle, but if that happens in the end of user gesture, the velocity for the next fling would be wrong. It shows a "bounce back" effect, and can be triggered when user makes small quick joystick scrolls in one direction.
**Problem two**
{F680821494}
There is a gap between animator's `onAnimationEnd` lifecycle method [finished](https://fburl.com/code/6baq04ne) and the `Animator#isRunning` API to return false. This is causing issues for `getPostAnimationScrollX` where we [decide to return](https://fburl.com/code/hzzugvch) the animated final value or the scroll value. User may see the `-1` value got used for the next fling start value, and the whole scroll view goes back to the beginning of scroll view and starts to fling.
This happens when the previous fling animation finishes and the animated final value is set to -1, but at the same time the next fling starts before `isRunning` returns false for the previous animation.
**Solution**
The problems are fixed by
- Do not reset animated final value to -1 in `onAnimationEnd` method
- Add `mIsFinished` states and use it to track animation finish signal, instead of using `isRunning` API
- Update logic where we decide to return the correct value for the next animation starts point. We will return previous animated final value when the animation got canceled, and user is going towards that value from the current scroll value.
Changelog:
[Android][Fixed] - Fixed edge case for quick small scrolls causing unexpected scrolling behaviors.
Reviewed By: javache
Differential Revision: D32487846
fbshipit-source-id: f1b0647656e021390e3a05de5846251a4a2647ff
React Native
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