flutter AutomaticKeepAliveClientMixin不起作用？

参考 https://www.colabug.com/3162835.html
https://stackoverflow.com/questions/53011686/flutter-automatickeepaliveclientmixin-is-not-working-with-bottomnavigationbar62835.html

Flutter切换tab后保留tab状态 概述 Flutter中为了节约内存不会保存widget的状态,widget都是临时变量。当我们使用TabBar,TabBarView是我们就会发现,切换tab，initState又会被调用一次。
怎么为了让tab一直保存在内存中，不被销毁？
添加AutomaticKeepAliveClientMixin，并设置为true,这样就能一直保持当前不被initState了。

class TicketListViewState extends State
    with AutomaticKeepAliveClientMixin {
  @override
  void initState() {
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    super.build(context);
    return new SmartRefresher(
        enablePullDown: true,
        enablePullUp: true,
        onRefresh: _onRefresh,
        controller: refreshController,
        child: ListView.builder(
          itemCount: _result.length,
          itemBuilder: (context, index) {
            return getItem(_result[index]);
          },
        ));
  }
  //不会被销毁,占内存中
  @override
  bool get wantKeepAlive => true;
}

如果不起作用

  @override
  Widget build(BuildContext context) {
    super.build(context);//必须添加
   .....
        ));

官方解释

/// A mixin with convenience methods for clients of [AutomaticKeepAlive]. Used
/// with [State] subclasses.
///
/// Subclasses must implement [wantKeepAlive], and their [build] methods must
/// call `super.build` (the return value will always return null, and should be
/// ignored).