Scrolling in WebViews leads to ViewPager page swipes

[tobiasrohloff]

Scrolling in WebViews leads to ViewPager page swipes

[bengelhaupt]

So I had a look into this, fiddled around a bit and the problem is indeed the communication between ViewPager2 and NestedScrollWebView. How ViewPager swiping works, is by intercepting the touch events from its inner views and checking whether the user swiped sideways. Other scrollable views call requestDisallowInterceptTouchEvent(true) when they do not want parent views to intercept touch events. NestedScrollWebView does not do this and touch events are handled by the ViewPager. The NestedScrollWebView's custom scroll handling supports horizontal and vertical scrolling. So calling requestDisallowInterceptTouchEvent(true) on startNestedScroll() and requestDisallowInterceptTouchEvent(false) on stopNestedScroll() does completely disable ViewPager swiping.

The feature has been broken because ViewPager2 also allows a vertical orientation, while ViewPager(1) only supports horizontal. So I guess in ViewPager(1) only vertical scrolling was allowed in the pager tabs and therefore the NestedScrollWebView.
The documentation says: "ViewPager2 does not natively support nested scroll views in cases where the scroll view has the same orientation as the ViewPager2 object that contains it. [...] To support a scroll view inside a ViewPager2 object with the same orientation, you must call requestDisallowInterceptTouchEvent() on the ViewPager2 object when you expect to scroll the nested element instead."

Solutions are either disabling ViewPager swiping for the selected tab or only allowing to scroll the NestedScrollWebView vertically.

[tobiasrohloff]

Hmm, disabling ViewPager swiping only for certain tabs sounds wrong to me and very confusing for users. The drawback of only allowing to scroll the NestedScrollWebView vertically is that web pages with bad responsiveness cannot be scrolled horizontally anymore, right? The latter sounds okay-ish to me.

[bengelhaupt]

Another idea would be to check whether there is "space to scroll" so pages that are already swiped to start allow viewpager swiping. But this would need a lot of custom touch handling.