Dart：如何在另一个 bloc 中正确调度 bloc 事件

Question

我需要在我的 LoginBloc 中访问 AuthenticationBloc，以便在登录成功时触发 AuthenticationLogin() 事件。到目前为止我所做的没有工作。

我做了什么：

class LoginBloc extends Bloc<LoginEvent, LoginState> {
  final AuthenticationBloc authenticationBloc;
  final AuthenticateCredentialsUsecase authenticateCredentialsUsecase;

//code

  Stream<LoginState> mapEventToState(
    LoginEvent event,
  ) async* {
        //code
        authenticationBloc.add(AuthenticationLogin());
        yield LoginLoadSuccess();
        //code
  }
}

我想要完成的事情：

class _AppViewState extends State<AppView> {

  final _navigatorKey = GlobalKey<NavigatorState>();
  NavigatorState get _navigator => _navigatorKey.currentState;

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      navigatorKey: _navigatorKey,
      builder: (context, child) {
        return BlocListener<AuthenticationBloc, AuthenticationState>(
          listener: (context, state) {
             if (state is AuthenticationAuthenticated) {
                _navigator.pushAndRemoveUntil<void>(
                  HomePage.route(),
                  (route) => false,
                );
             }
             else if (state is AuthenticationUnauthenticated){
                _navigator.pushAndRemoveUntil<void>(
                  LoginScreen.route(),
                  (route) => false,
                );
             }
          },
          child: child,
        );
      },
      onGenerateRoute: (_) => SplashPage.route(),
    );
  }
}

如您所见，用户当前在 LoginScreen 中，一旦登录成功，我需要在 AuthenticationBloc() 中产生 AuthenticationAuthenticated() 状态，这样我的用户将被定向到 HomePage()

如何在我的 LoginBloc() 中产生 AuthenticationBloc() 的 AuthenticationAuthenticated() 状态 - 因为我的登录逻辑发生在 LoginBloc 中。

Answer 1

1. 我为 AuthenticationBloc 订阅了我的 AuthenticateCredentialsUsecase 类的状态流。
2. 当在我的 LoginBloc 中调用 AuthenticateCredentialsUsecase 并验证凭据时...
3. 然后我更新状态流 - _controller.add(AuthenticationStatus.authenticated);
4. 哪个会触发 AuthenticationLogin 事件 在 AuthenticationBloc 中

身份验证块

 AuthenticationBloc({
    @required CheckAuthenticationStatusUsecase checkAuthenticationStatus,
    @required LogoutAuthenticatedUserUsecase logoutAuthenticatedUser,
    @required AuthenticateCredentialsUsecase authenticateCredentials,
  })  : assert(checkAuthenticationStatus != null),
        assert(logoutAuthenticatedUser != null),
        assert(authenticateCredentials != null),
        checkAuthenticationStatusUsecase = checkAuthenticationStatus,
        logoutAuthenticatedUserUsecase = logoutAuthenticatedUser,
        authenticateCredentialsUsecase = authenticateCredentials,
        super(AuthenticationInitial()) {
    add(AuthenticationStatusRequested());
    _loginStatusSubscription =
        authenticateCredentialsUsecase.status.listen((event) {
      if (event == AuthenticationStatus.authenticated) {
        add(AuthenticationLogin());
      }
    });
  }

AuthenticateCredentialsUsecase

  final _controller = StreamController<AuthenticationStatus>();

  Stream<AuthenticationStatus> get status async* {
    yield AuthenticationStatus.unknown;
    yield* _controller.stream;
  }

  void dispose() => _controller.close();

  @override
  Future<Either<Failure, AuthenticatedUser>> call(AuthenticationParams params) async {

    final result = await repository.authenticateCredentials(params.userName, params.password);

    if(result is Right){
      _controller.add(AuthenticationStatus.authenticated);
    }

    return result;
  }

Answer 2

这是一种方法。您必须调用 BlocBuilder 来处理构建小部件以响应新状态。

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      debugShowCheckedModeBanner: false,
      home: BlocBuilder<AuthenticationBloc, AuthenticationState>(
        builder: (context, state) {
          //If the login is successful, show homepage
          if (state is AuthenticationAuthenticated) {
            return HomePage();
          }
          //If the login failed, show login screen
          if (state is AuthenticationUnauthenticated) {
            return LoginScreen();
          }
          //If the login is in process, show loading indicator
          if (state is AuthenticationInProgress) {
            return LoadingIndicator();
          }
          return SplashScreen();
        },
      ),
    );
  }
}

一开始，状态为AuthenticationUnauthenticated，并显示登录屏幕。如果登录成功，则显示主页，否则，如果登录失败，则显示 LoginScreen。

class LoginBloc extends Bloc<LoginEvent, LoginState> {
  final AuthenticationBloc authenticationBloc;
  final AuthenticateCredentialsUsecase authenticateCredentialsUsecase;

//code

  Stream<LoginState> mapEventToState(
    LoginEvent event,
  ) async* {

    if(event is LoginButtonPressed) {
        // some logic code
        // eg. : final response = UserRepository.login(username: event.username, password: event.password);
            authenticationBloc.add(AuthenticationLogin());
            //code

    }
        
  }
}

这是处理身份验证的 AuthenticationBloc () 代码。

 class AuthenticationBloc extends Bloc<AuthenticationEvent, AuthenticationState>{
    
    //code
    
      Stream<AuthenticationState> mapEventToState(
        AuthenticationEvent event,
      ) async* {
          if(event is AuthenticationLogin) {
             yield AuthenticationInProgress();
             //code
             yield AuthenticationAuthenticated();
          }
    }
}