code: public long getChildItemId(View child) {
          if (mAdapter == null || !mAdapter.hasStableIds()) {
              return NO_ID;
          }
          final ViewHolder holder = getChildViewHolderInt(child);
          return holder != null ? holder.getItemId() : NO_ID;
      }
docs: Return the stable item id that the given child view corresponds to.
  
  @param child Child View to query
  @return Item id corresponding to the given view or {@link #NO_ID}