code: private void assignClickListenerRecursively(View parent) {
      if (parent == null) {
        return;
      }
  
      if (parent instanceof ViewGroup) {
        ViewGroup viewGroup = (ViewGroup) parent;
        int childCount = viewGroup.getChildCount();
        for (int i = childCount - 1; i >= 0; i--) {
          View child = viewGroup.getChildAt(i);
          assignClickListenerRecursively(child);
        }
      }
      setClickListener(parent);
    }
docs: Loop among the views in the hierarchy and assign listener to them