maintain correct content offset when scroll view is suspended

[sammy-SC]

Summary:

Changelog:

[iOS] [Fixed] - Preserve content offset in ScrollView when the component is suspended

The problem

On iOS, components are recycled. For ScrollView, its content offset has to be reset back to original position. When we call [UIScrollView setContentOffset:], it triggers all of its delegate methods and triggers scrollViewDidScroll where we set native state.

So when user scrolls to position 100 and scroll view suspends. it is removed from view hierarchy and recycled. Once the suspense boundary is resolved, scroll view will be inserted back into view hierarchy. But when it was recycled, we set back its original content offset (the default is 0, 0) but this was accidentally propagated through to shadow tree.

Solution

To avoid this, we simply need to invalidate _state before calling [UIScrollView setContentOffset:].

Differential Revision: D56573370