尽管观察器中的状态发生了变化，但是为什么应用重启后Flutter BloC UI没有更新？

class MyBloc {
  final _myStreamController = StreamController<String>();

  Stream<String> get myStream => _myStreamController.stream;

  // ...
}

class MyWidget extends StatelessWidget {
  final MyBloc _bloc = MyBloc();

  @override
  Widget build(BuildContext context) {
    return StreamBuilder<String>(
      stream: _bloc.myStream,
      builder: (context, snapshot) {
        if (snapshot.hasData) {
          // 更新UI
          return Text(snapshot.data);
        } else {
          // 显示加载中或默认UI
          return CircularProgressIndicator();
        }
      },
    );
  }
}

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  final MyBloc _bloc = MyBloc();

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: MyWidget(),
    );
  }
}