Vojtech Novak 9e85b7ad88 ScrollView, HorizontalScrollView: do not ignore null contentOffset prop (#28760)
Summary:
motivation: I was just checking out https://github.com/facebook/react-native/commit/30cc158a875a0414cf53d4d5155410eea5d5aeea
and noticed that the commit, I believe, is missing logic for when `contentOffset` is actually `null`.

That is, consider you render `ScrollView` with `contentOffset` { x: 0, y: 100 } and then change that to null / undefined. I'd expect the content offset to invalidate (set to 0 - hope that's the default).

## Changelog

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https://github.com/facebook/react-native/wiki/Changelog
-->

[Android] [Fixed] - ScrollView, HorizontalScrollView: do not ignore `null` `contentOffset` prop
Pull Request resolved: https://github.com/facebook/react-native/pull/28760

Test Plan:
Tested locally within RNTester

<details><summary>code</summary>
<p>

```js
const Ex = () => {
  let _scrollView: ?React.ElementRef<typeof ScrollView> = React.useRef(null);
  const [offset, setOffset] = React.useState({x: 0, y: 20});
  setTimeout(() => {
    setOffset(undefined);
  }, 2000);

  return (
    <View>
      <ScrollView
        ref={_scrollView}
        automaticallyAdjustContentInsets={false}
        onScroll={() => {
          console.log('onScroll!');
        }}
        contentOffset={offset}
        scrollEventThrottle={200}
        style={styles.scrollView}>
        {ITEMS.map(createItemRow)}
      </ScrollView>
      <Button
        label="Scroll to top"
        onPress={() => {
          nullthrows(_scrollView.current).scrollTo({y: 0});
        }}
      />
      <Button
        label="Scroll to bottom"
        onPress={() => {
          nullthrows(_scrollView.current).scrollToEnd({animated: true});
        }}
      />
      <Button
        label="Flash scroll indicators"
        onPress={() => {
          nullthrows(_scrollView.current).flashScrollIndicators();
        }}
      />
    </View>
  );
};
```

</p>
</details>

Reviewed By: shergin

Differential Revision: D22298676

Pulled By: JoshuaGross

fbshipit-source-id: e411ba4c8a276908e354d59085d164a38ae253c0
2020-06-30 12:52:06 -07:00
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