class CollectionView extends FrameLayout {

  void showLoading() {
    if (adapter == null) {
      throw new NullPointerException("adapter is null");
    }
    if (getChildCount() == 2) {
      removeViewAt(1);
    }
    refreshLayout.setRefreshing(true);
  }

  public  CollectionView(
      @NonNull Context context,
      @Nullable AttributeSet attrs);

}