docs: public void setAreHeadersSticky(boolean areHeadersSticky) {
          mAreHeadersSticky = areHeadersSticky;
          if (!areHeadersSticky) {
              clearHeader();
          } else {
              updateOrClearHeader(mList.getFixedFirstVisibleItem());
          }
          // invalidating the list will trigger dispatchDraw()
          mList.invalidate();
      }