Question

我正在使用BLoC，我需要从PageOne导航到PageTwo，并能够使用“后退”按钮返回，我不知道这是否是解决此问题的正确方法。调用函数 _navigateToPage2 时也会出错。

用于从导航器推送或弹出路由的上下文必须是作为导航器小部件的后代的小部件的上下文。

class SimpleBlocDelegate extends BlocDelegate {

  @override
  void onTransition(Transition transition) {
     print(transition);
  }

  @override
  void onError(Object error, StackTrace stacktrace) {
      print(error);
   }
}



void main() {
  BlocSupervisor().delegate = SimpleBlocDelegate();
  runApp(MyApp(userRepository: UserRepository(GuriApi())));
}

class MyApp extends StatefulWidget {
  final UserRepository userRepository;

  MyApp({Key key, @required this.userRepository}) : super(key: key);

  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  AuthenticationBloc _authenticationBloc;
  UserRepository get _userRepository => widget.userRepository;

  @override
  void initState() {
    _authenticationBloc = AuthenticationBloc(userRepository: _userRepository);
    _authenticationBloc.dispatch(AppStarted());
    super.initState();
  }

  @override
  void dispose() {
    _authenticationBloc.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return BlocProvider<AuthenticationBloc>(
      bloc: _authenticationBloc,
      child: MaterialApp(
        theme: new ThemeData(
            fontFamily: 'Monserrat',
            primaryColor: Colors.lightBlue[50],
            accentColor: Colors.white),
        home: BlocBuilder<AuthenticationEvent, AuthenticationState>(
          bloc: _authenticationBloc,
          builder: (BuildContext context, AuthenticationState state) {
            if (state is AuthenticationUninitialized) {
              return SplashPage();
            }
            if (state is AuthenticationAuthenticated) {
              return Home(userRepository: _userRepository);
            }
            if (state is AuthenticationUnauthenticated) {
              return LoginPage(userRepository: _userRepository);
            }
            if (state is AuthenticationLoading) {
              return LoadingIndicator();
            }
            if (state is PageOneSelected) {
              return PageOne();
            }
            if (state is PageTwoSelected) {
              _navigateToPage2();
            }
          },
        ),
      ),
    );
  }

  _navigateToPage2() {
    Navigator.of(context).push<bool>(
        MaterialPageRoute(
            builder: (BuildContext context) =>
                PageTwo(userRepository: _userRepository)));
  }
}

Answer 1

我认为最好通过订阅initState中的状态更改来处理导航：

@override
void initState() {
    super.initState();

    bloc.state.listen((state) {
        if (state is PageOneSelected) {
            _navigateToPage2();
        } else if (state is PageTwoSelected) {
            _navigateToPage2();
        }
    });
}

在构建方法中显示其他一些小部件。您的代码中发生错误，因为blocBuilder必须返回Widget，但是在PageTwoSelected状态下，您什么也不返回。

Answer 2

有必要在小部件中执行以下操作：

     if (state is PageTwoSelected) {
         WidgetsBinding.instance.addPostFrameCallback((_){
            Navigator.push(context, 
              MaterialPageRoute(builder: (context) =>
                PageTwo(userRepository: _userRepository))
            );
         });
     }

这是必要的，因为如果在仍在构建小部件（处于脏状态）的同时进行导航，则Flutter将抛出异常。

通过将其嵌套在addPostFrameCallback的回调中，您基本上是在说完成小部件的构建，然后执行导航代码。

您可以详细了解here，评论中有解释。

使用BLoC进行Flutter导航：用于从Navigator推送路由的上下文必须是Navigator小部件的后代

2 个答案: