Flutter onPressed 异步函数不等待来自 cubit/repository 的 await 函数

Question

我有一个注册按钮，它向我的 API 发送一个 http 请求。我想在请求完成后离开注册页面。使用 bloc 模式，我向 bloc 添加了一个事件以导航到登录页面，但注册页面在将事件添加到 bloc 之前没有等待 http 请求完成。

注册按钮代码：-

class _SignUpButton extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return BlocBuilder<SignUpCubit, SignUpState>(
      buildWhen: (previous, current) => previous.status != current.status,
      builder: (context, state) {
        return state.status.isSubmissionInProgress
            ? const CircularProgressIndicator()
            : IconButton(
                key: const Key('loginForm_continue_raisedButton'),
                onPressed: state.status.isValidated
                    ? () async {
                      await context.bloc<SignUpCubit>().signUpFormSubmitted();
                      context.bloc<AuthenticationBloc>().add(AuthenticationUserChanged(User.empty));
                    }
                    : () => print('invalid'),
                icon: Icon(Icons.keyboard_arrow_right),
                color: Colors.white,
                iconSize: 40,
              );
      },
    );
  }
}

报名肘：-

part 'signup_state.dart';

class SignUpCubit extends Cubit<SignUpState> {
  SignUpCubit(this._authenticationRepository)
      : assert(_authenticationRepository != null),
        super(const SignUpState());

  final AuthenticationRepository _authenticationRepository;

  //irrelevant code omitted

  Future<void> signUpFormSubmitted() async {
    if (!state.status.isValidated) return;
    emit(state.copyWith(status: FormzStatus.submissionInProgress));
    try {
      await _authenticationRepository.signUp(
          name: state.name,
          password: state.password.value,
          mobile: state.mobile.value,
          village: state.village,
          email: state.email.value,
          pincode: state.pincode);
      emit(state.copyWith(status: FormzStatus.submissionSuccess));
    } on Exception {
      emit(state.copyWith(status: FormzStatus.submissionFailure));
    }
  }
}

身份验证存储库：-

/// Thrown if during the sign up process if a failure occurs.
class SignUpFailure implements Exception {}

class AuthenticationRepository {
  /// {@macro authentication_repository}
  AuthenticationRepository({
    FirebaseAuth firebaseAuth,
    GoogleSignIn googleSignIn,
  })  : _firebaseAuth = firebaseAuth ?? FirebaseAuth.instance,
        _googleSignIn = googleSignIn ?? GoogleSignIn.standard();

  final FirebaseAuth _firebaseAuth;
  final GoogleSignIn _googleSignIn;

  /// Stream of [User] which will emit the current user when
  /// the authentication state changes.
  ///
  /// Emits [User.empty] if the user is not authenticated.
  Stream<User> get user {
    return _firebaseAuth.onAuthStateChanged.map((firebaseUser) {
      return firebaseUser == null ? User.empty : firebaseUser.toUser;
    });
  }

  //irrelevant code omitted

  Future<void> signUp(
      {@required String name,
      @required String password,
      @required String mobile,
      @required String village,
      @required String pincode,
      @required String email}) async {
    assert(
        name != null && mobile != null && village != null && pincode != null);
    try {
      if (email != '' && password != '') {
        await _firebaseAuth.createUserWithEmailAndPassword(
            email: email, password: password);
      }
      final params = {
        'name': name,
        'phone': mobile,
        'village': village + '_' + pincode,
        'api': 't',
        'login': 'NA'
      };
      Response res = await Dio().get(
          "https://us-central1-greensat-9087a.cloudfunctions.net/addUser",
          queryParameters: params);
      print(res.data);
    } on Exception {
      throw SignUpFailure();
    }
  }  

}

身份验证块：-

class AuthenticationBloc
    extends Bloc<AuthenticationEvent, AuthenticationState> {
  AuthenticationBloc({
    @required AuthenticationRepository authenticationRepository,
  })  : assert(authenticationRepository != null),
        _authenticationRepository = authenticationRepository,
        super(const AuthenticationState.unknown()) {
    _userSubscription = _authenticationRepository.user.listen(
      (user) => add(AuthenticationUserChanged(user)),
    );
  }

  final AuthenticationRepository _authenticationRepository;
  StreamSubscription<User> _userSubscription;

  @override
  Stream<AuthenticationState> mapEventToState(
    AuthenticationEvent event,
  ) async* {
    if (event is AuthenticationUserChanged) {
      yield _mapAuthenticationUserChangedToState(event);
    } else if (event is AuthenticationLogoutRequested) {
      unawaited(_authenticationRepository.logOut());
    } else if (event is AuthenticationOTPRequested) {
      yield _mapAuthenticationUserOTPRequested(event);
    } else if (event is AuthenticationSignupStarted) {
      yield _mapAuthenticationUserSignupStarted(event);
    }
  }

  @override
  Future<void> close() {
    _userSubscription?.cancel();
    return super.close();
  }

  AuthenticationState _mapAuthenticationUserChangedToState(
    AuthenticationUserChanged event,
  ) {
    print('user changed state');
    print(event.user);
    return event.user != User.empty
        ? AuthenticationState.authenticated(event.user)
        : const AuthenticationState.unauthenticated();
  }

  AuthenticationState _mapAuthenticationUserOTPRequested(
    AuthenticationOTPRequested event,
  ) {
    return const AuthenticationState.unauthenticatedOTP();
  }

  AuthenticationState _mapAuthenticationUserSignupStarted(
    AuthenticationSignupStarted event,
  ) {
    return const AuthenticationState.signupStarted();
  }
}

Answer 1

你不能在 cubit 发射器函数中使用异步

不正确：⛔️

void increment() async => emit(state+1)

正确：✅

void increment() => emit(state+1)