docs: public void onItemBind(int position, T item) {
          if (onItemBind != null) {
              variableId = VAR_INVALID;
              layoutRes = LAYOUT_NONE;
              onItemBind.onItemBind(this, position, item);
              if (variableId == VAR_INVALID) {
                  throw new IllegalStateException("variableId not set in onItemBind()");
              }
              if (layoutRes == LAYOUT_NONE) {
                  throw new IllegalStateException("layoutRes not set in onItemBind()");
              }
          }
      }