code: public void deselect() {
          SelectExtension<Item> selectExtension = mFastAdapter.getExtension(SelectExtension.class);
          if (selectExtension == null) {
              return;
          }
          for (Item item : AdapterUtil.getAllItems(mFastAdapter)) {
              selectExtension.deselect(item);
          }
          mFastAdapter.notifyDataSetChanged();
      }
docs: deselects all selections