code: private void enhanceFAB(final FloatingActionButton fab, MotionEvent e) {
          if (hasAllItemsShown()) {
              if (fab.getVisibility() != View.VISIBLE) {
                  fab.show();
              }
          }
      }
docs: Enhanced FAB UX Logic
  Handle RecyclerView scrolled
  If all item visible within view port, FAB will show
  
  @param fab FloatingActionButton
  @param e   MotionEvent