Detect swiping out of bounds in Android's ViewPager2

Question

I'm using ViewPager2 and want to detect when the user swipes either to the left on the first page or the right on the last page.

I know this can be implemented using the old ViewPager like discussed here, but this approach is not feasible since ViewPager2 is final and can't be subclassed.

ViewPager2 provides the OnPageChangeCallback but this can't be used either since there are no page events when swiping out of bounds.

Am I missing something?

Answer 1

I figured out a (slighly hacky) solution while I was typing this question.

It is based on the observation that the state SCROLL_STATE_SETTLING is only reached when the viewpager really settles on a new page. If there is only fruitless dragging on the first or last page then only the states SCROLL_STATE_DRAGGING and finally SCROLL_STATE_IDLE are passed.

viewPager.registerOnPageChangeCallback(new ViewPager2.OnPageChangeCallback() {

        private boolean settled = false;

        @Override
        public void onPageScrollStateChanged(int state) {
            super.onPageScrollStateChanged(state);
            if (state == SCROLL_STATE_DRAGGING) {
                settled = false;
            }
            if (state == SCROLL_STATE_SETTLING) {
                settled = true;
            }
            if (state == SCROLL_STATE_IDLE && !settled) {
                doYourOutOfBoundsStuff();
            }
        }
    });

I'm not entirely happy, but this is the best I came across so far.