Summary:
This adds support for pagingEnabled to the HorizontalScrollView.
This is an initial implementation.
Because Android doesn't provide great details about what is happening with a scroll view after you are done touching it, we have some post touch handling. This is kicked off either by touch up or a fling call.
Once we are doing that handling, we start a runnable that basically checks if we are still scrolling. If we are, we just schedule that runnable again and check a frame later. If we are done scrolling (no onScrollChanged since we last fired), we could be in one of two states, the fling is done or we are done snapping to the page boundary. If we are in the fling done case, we then check if we need to scroll to a page boundary. If so, we call smoothScrollTo and schedule ourself to check onScroll events again until done with that scroll. If we are done with both (either we only did momentum scroll or we did that and then snapped to page), we can then fire the final event and stop checking. This logic is all in handlePostTouchScrolling.
Because of the decision to only do page scrolling after momentum ends, we do allow you to scroll through with momentum a number of pages and the transition can be a little strange where it stops a sec and then slides to be page aligned. As a follow up, we can probably smooth that up by changing the value we pass to super.fling() that would adjust it to be let momentum carry it to the page boundary.
Reviewed By: weicool
Differential Revision: D3207608
fb-gh-sync-id: 02f62970ed9a5e3a5f9c0d959402756bc4b3699e
fbshipit-source-id: 02f62970ed9a5e3a5f9c0d959402756bc4b3699e
a3146e41a2