protected int getAvailableScrollHeight(int adapterHeight, int yOffset) {
        int visibleHeight = getHeight();
        int scrollHeight = getPaddingTop() + yOffset + adapterHeight + getPaddingBottom();
        return scrollHeight - visibleHeight;
    }
Returns the available scroll height:
AvailableScrollHeight = Total height of the all items - last page height

@param yOffset the offset from the top of the recycler view to start tracking.
android/third_party/recyclerview-fastscroll/src/main/java/com/simplecityapps/recyclerview_fastscroll/views/FastScrollRecyclerView.java