Summary:
Sometimes is handy to check if a React node is a descendant of another node or not. For instance, I want to check if the focused `TextInput` is descendant of an specific `ScrollView`:
```js
const currentlyFocusedField = TextInput.State.currentlyFocusedField()
UIManager.viewIsAncestorOf(
currentlyFocusedField,
this.getInnerViewNode(),
(isAncestor) => {
if (isAncestor) {
console.log('The focused field is a descendant of this ScrollView!')
}
}
)
```
This function uses the same strategy as the `measureLayout` method to check if one node is an ancestor of other node. As the `measureLayout` method, this is performed outside the main thread.
By now I've only implemented the iOS version and its tests, but if this function is going to be merged I'll implement the Android version too. I have objc experience but no Java or Android, so I prefer to validate this functionality before jumping into developing the Android part.
Closes https://github.com/facebook/react-native/pull/7876
Differential Revision: D3662045
Pulled By: javache
fbshipit-source-id: b9668e8ea94fd01db76651f16243926cf9c2566f
e52cab5a7f