code: @Nullable
      public FastAdapter<Item> getFastAdapter(RecyclerView.ViewHolder viewHolder) {
          Object tag = viewHolder.itemView.getTag(R.id.fastadapter_item_adapter);
          if (tag instanceof FastAdapter) {
              return (FastAdapter<Item>) tag;
          }
          return null;
      }
docs: Helper method to get the FastAdapter from this ViewHolder
  
  @param viewHolder
  @return