public void setOnFastScrollStateChangeListener(OnFastScrollStateChangeListener stateChangeListener) {
        mStateChangeListener = stateChangeListener;
    }
Calculates the total height of the recycler view. This method should only be called when the
attached adapter implements {@link MeasurableAdapter}.

@return The total height of all rows in the RecyclerView
android/third_party/recyclerview-fastscroll/src/main/java/com/simplecityapps/recyclerview_fastscroll/views/FastScrollRecyclerView.java