boolean pageDown() {
        if (mAdapter != null && mCurItem < (mAdapter.getCount() - 1)) {
            setCurrentItem(mCurItem + 1, true);
            return true;
        }
        return false;
    }
You can call this function yourself to have the scroll view perform
scrolling from a key event, just as if the event had been dispatched to
it by the view hierarchy.

@param event The key event to execute.
@return Return true if the event was handled, else false.
dkplayer-sample/src/main/java/xyz/doikki/dkplayer/widget/VerticalViewPager.java