@Override
        public int compare(ItemInfo lhs, ItemInfo rhs) {
            return lhs.position - rhs.position;
        }
Used to track what the expected number of items in the adapter should be.
If the app changes this when we don't expect it, we'll throw a big obnoxious exception.
dkplayer-sample/src/main/java/xyz/doikki/dkplayer/widget/VerticalViewPager.java