anchor.diff:    _renderTopicGroup(BuildContext context) {
       if (widget.reposHeaderViewModel.topics == null ||
           widget.reposHeaderViewModel.topics.length == 0) {
  -      return Container();
  +      return Container(
  +        key: layoutTopicContainerKey,
  +      );
       }
       List<Widget> list = new List();
       for (int i = 0; i < widget.reposHeaderViewModel.topics.length; i++) {
  
positive.code:       RenderBox renderBox2 =
            layoutTopicContainerKey.currentContext?.findRenderObject();
  
        /// 最后面的一个tag
        RenderBox renderBox3 =
            layoutLastTopicKey.currentContext?.findRenderObject();
        double overflow = ((renderBox3?.localToGlobal(Offset.zero)?.dy ?? 0) -
                (renderBox2?.localToGlobal(Offset.zero)?.dy ?? 0)) -
            (layoutLastTopicKey.currentContext?.size?.height ?? 0);
        var newSize;
        if (overflow > 0) {
          newSize = layoutKey.currentContext.size.height + overflow;
        } else {
          newSize = layoutKey.currentContext.size.height + 10.0;
        }
        if (Config.DEBUG) {
          print("newSize $newSize overflow $overflow");
        }
        if (widgetHeight != newSize && newSize > 0) {
          print("widget?.layoutListener?.call");
          widgetHeight = newSize;
          widget?.layoutListener
              ?.call(Size(layoutKey.currentContext.size.width, widgetHeight));
        }
      });
    }
  
  
negative.code:     return new Container(
        key: layoutTopicContainerKey,
        alignment: Alignment.topLeft,
        //margin: EdgeInsets.only(top: 5.0),
        child: Wrap(
          spacing: 10.0,
          runSpacing: 5.0,
  