失败的断言：第 515 行 pos 12：'haveDimensions == (_lastMetrics != null)'：不是真的

Question

我在应用 scrollController Failed 断言时收到此错误：第 515 行 pos 12: 'haveDimensions == (_lastMetrics != null)': 不正确。

void initState() {
    super.initState();
    _scrollController = ScrollController();
    _scrollController.addListener(_scrollListener);
  } 

_scrollListener() {
    if (selectedcard == 0) {

      _scrollController.animateTo(_scrollController.offset + 120,
          curve: Curves.linear, duration: Duration(milliseconds: 500));
    }
  }


 child: CircleListScrollView(
                controller: _scrollController,
                physics: CircleFixedExtentScrollPhysics(),
                ................
);