由于mapEventToState導致的Flutter塊遷移不起作用

我正在關注遷移到新的 bloc 8.0.0。我正在嘗試洗掉mapEventToState 但我在這樣做時遇到了困難。你能幫我怎么做嗎。我已經在下面嘗試過，但它不起作用。

舊代碼：

class SignInBloc extends Bloc<SignInEvent, SignInState> {
  final AuthenticationRepository authenticationRepository;
  final UserDataRepository userDataRepository;

  SignInBloc(
      {required this.authenticationRepository,
      required this.userDataRepository})
      : super(SignInInitialState());

  SignInState get initialState => SignInInitialState();

  @override
  Stream<SignInState> mapEventToState(
    SignInEvent event,
  ) async* {
    if (event is SignInWithGoogle) {
      yield* mapSignInWithGoogleToState();
    }
  }

Stream<SignInState> mapSignInWithGoogleToState() async* {
    yield SignInWithGoogleInProgressState();
    try {
      String res = await authenticationRepository.signInWithGoogle();
      yield SignInWithGoogleCompletedState(res);
    } catch (e) {
      print(e);
      yield SignInWithGoogleFailedState();
    }
  }
...

遷移代碼（不起作用）：

class SignInBloc extends Bloc<SignInEvent, SignInState> {
  final AuthenticationRepository authenticationRepository;
  final UserDataRepository userDataRepository;

  SignInBloc(
      {required this.authenticationRepository,
        required this.userDataRepository})
      : super(SignInInitialState())
  {
    SignInState get initialState => SignInInitialState();

    on<SignInWithGoogle>((event, emit) => emit(mapSignInWithGoogleToState()));
  }

Stream<SignInState> mapSignInWithGoogleToState() async* {
    yield SignInWithGoogleInProgressState();
    try {
      String res = await authenticationRepository.signInWithGoogle();
      yield SignInWithGoogleCompletedState(res);
    } catch (e) {
      print(e);
      yield SignInWithGoogleFailedState();
    }
  }
...

uj5u.com熱心網友回復：

您的問題是mapSignInWithGoogleToState()回傳一個狀態Stream，但新結構需要在emit每次需要發出新狀態時顯式呼叫。

class SignInBloc extends Bloc<SignInEvent, SignInState> {
  final AuthenticationRepository authenticationRepository;
  final UserDataRepository userDataRepository;

  SignInBloc({required this.authenticationRepository,
    required this.userDataRepository})
      : super(SignInInitialState()) {
    on<SignInWithGoogle>(mapSignInWithGoogleToState);
  }

  Future<void> mapSignInWithGoogleToState(
      SignInWithGoogle event,
      Emitter<SignInState> emit,
  ) async {
    emit(SignInWithGoogleInProgressState());
    try {
      String res = await authenticationRepository.signInWithGoogle();
      emit(SignInWithGoogleCompletedState(res));
    } catch (e) {
      print(e);
      emit(SignInWithGoogleFailedState());
    }
  }
}

這里有一些關于“為什么？”的更多資訊：https : //bloclibrary.dev/#/migration ? id=rationale-6

uj5u.com熱心網友回復：

getter 不屬于建構式體，我想它不再需要了。你可以這樣解決問題：

class SignInBloc extends Bloc<SignInEvent, SignInState> {
  final AuthenticationRepository authenticationRepository;
  final UserDataRepository userDataRepository;

  SignInBloc({required this.authenticationRepository,
    required this.userDataRepository})
      : super(SignInInitialState()) {
    on<SignInWithGoogle>(_handleSignInWithGoogleEvent);
  }

  Future<void> _handleSignInWithGoogleEvent(
      SignInWithGoogle event,
      Emitter<SignInState> emit,
  ) async {
    // TODO do your thing and create and emit the SignInWithGoogleState
    emit(SignInWithGoogleState());
  }
}

請注意，bloc v8 中的事件不再按順序處理，而是并發處理。閱讀這篇博文：https : //verygood.ventures/blog/how-to-use-bloc-with-streams-and-concurrency

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