InheritedWidget

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return RootWidget(
      child: MaterialApp(
        debugShowCheckedModeBanner: false,
        title: 'V2EX app',
        theme: ThemeData(
          primarySwatch: Colors.grey,
        ),
        initialRoute: '/',
        routes: {
          '/': (context) => HomePage(),
          '/nodes': (context) => NodePage(),
          '/test': (context) => TestApp(),
//          '/web': (context) => WebTest(),
        },
      ),
      bloc: UserBloc(),
    );
  }
}

　　

class RootWidget extends InheritedWidget {
  RootWidget({this.bloc, this.child}) : super(child: child);
  final UserBloc bloc;
  final Widget child;

  static RootWidget of(BuildContext context) =>
      (context).inheritFromWidgetOfExactType(RootWidget);

  @override
  bool updateShouldNotify(InheritedWidget oldWidget) {
    return true;
  }
}