code: @UiThread
      public int getParentAdapterPosition() {
          int flatPosition = getAdapterPosition();
          if (mExpandableAdapter == null || flatPosition == RecyclerView.NO_POSITION) {
              return RecyclerView.NO_POSITION;
          }
  
          return mExpandableAdapter.getNearestParentPosition(flatPosition);
      }
docs: Returns the adapter position of the Parent associated with this ChildViewHolder
  
  @return The adapter position of the Parent if it still exists in the adapter.
  RecyclerView.NO_POSITION if item has been removed from the adapter,
  RecyclerView.Adapter.notifyDataSetChanged() has been called after the last
  layout pass or the ViewHolder has already been recycled.