返回类型“SliverAppBar？” 不是&#39;列表<Widget> &#39;，根据闭包上下文的要求

Question

//I do not know why here is an error I wrote the class, then the function, and when I called, I returned the return.

class WhatsAppHomeState extends State<WhatsAppHome>
    with SingleTickerProviderStateMixin {
  late TabController tabController;
  late Map<String, SliverAppBar> appBarList;
  String _currentAppBar = 'mainAppBar';

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    tabController = new TabController(initialIndex: 1, length: 4, vsync: this);

    SliverAppBar mainAppBar = new SliverAppBar(...);
      

    appBarList = <String, SliverAppBar>{
      'mainAppBar': mainAppBar,
      'searchAppBar': mainAppBar
    };
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      body: new NestedScrollView(
        headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
          return appBarList[_currentAppBar]];//I do not know why here is an error
        },..

. . .

Answer 1

headerSliverBuilder needs a list of widgets:

headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) {
          return <Widget>[
                appBarList[_currentAppBar]]
              ];
        }