code: @Override
  	public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
  		boolean bCanScrollUp;
  		if (android.os.Build.VERSION.SDK_INT < 14) {
  			bCanScrollUp = view.getChildCount() > 0
  				&& (view.getFirstVisiblePosition() > 0 ||
  				view.getChildAt(0).getTop() < view.getPaddingTop());
  		} else {
  			bCanScrollUp = ViewCompat.canScrollVertically(view, -1);
  		}
  		showToolbarElevation(bCanScrollUp);
  	}
docs: /* Show header elevation when listview can scroll up; flatten header when listview
  scrolls to the top; For pre-llolipop devices, fallback to a divider