flutter : Mixins 不能被实例化

如何解决flutter : Mixins 不能被实例化

我现在使用的是 Flutter 旧版本，我正在更新最新版本。在这个核心的旧版本中运行良好，但是当我更新最新版本时，这不起作用，无法实例化 Mixins。 dart（mixins 实例化）[14,30] 抖动错误。请帮我解决这个问题。

源代码：

错误行屏幕短：https://prnt.sc/12yc5h9

sidebarlayout.dart

class SideBarLayout extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: BlocProvider<NavigationBloc>(
        create: (context) => NavigationBloc(),child: Stack(
          children: <Widget>[
            BlocBuilder<NavigationBloc,NavigationStates>(
              builder: (context,navigationState) {
                return navigationState as Widget;
              },),SideBar(),],);
  }
}

navigation.dart

enum NavigationEvents {
  HomePageClickedEvent,MyAccountClickedEvent,MyOrdersClickedEvent,SignUpClickedEvent,SignInClickedEvent,}

abstract class NavigationStates {}

mixin NavigationBloc implements Bloc<NavigationEvents,NavigationStates> {
  @override
  NavigationStates get initialState => MyAccountsPage();

  @override
  Stream<NavigationStates> mapEventToState(NavigationEvents event) async* {
    switch (event) {
      case NavigationEvents.HomePageClickedEvent:
        yield HomePage();
        break;
      case NavigationEvents.MyAccountClickedEvent:
        yield MyAccountsPage();
        break;
      case NavigationEvents.MyOrdersClickedEvent:
        yield MyOrdersPage();
        break;
      case NavigationEvents.SignUpClickedEvent:
        yield SignupPage();
        break;
      case NavigationEvents.SignInClickedEvent:
        yield SigninPage();
        break;
    }
  }
}

希望我能得到解答区，谢谢你们。