Flutter Bloc How to emit inside a listener

Issue

I have wanted to set up authentication using Firebase. I have this auth repository that has this method that gets the current user.

@override
Stream<User?> get user => _firebaseAuth.userChanges();

Inside my bloc, I Have this constructor.

class AuthBloc extends Bloc<AuthEvent, AuthState> {
  final AuthRepository _authRepository;
  late StreamSubscription<User?> _authSubscription;

  AuthBloc(AuthRepository authRepository)
      : _authRepository = authRepository,
        super(const AuthState.initial()) {
    on<AuthStarted>(_onUserChanged);
  }

  void _onUserChanged(AuthStarted event, Emitter<AuthState> emit) {
    _authSubscription = _authRepository.user.listen((user) async {
      if (user != null) {
        emit(AuthState.authenticated(user));
      } else {
        const AuthState.unauthenticated();
      }
    });
  }
}

When my app starts, I’m calling this on my main class.

 BlocProvider<AuthBloc>(
            create: (context) => AuthBloc(context.read<AuthRepository>())
              ..add(const AuthEvent.started()),
          ),

This is how my state looks like

part of 'auth_bloc.dart';

@freezed
class AuthState with _$AuthState {
  const factory AuthState.initial() = _initial;
  const factory AuthState.authenticated(User user) = _Authenticated;
  const factory AuthState.unauthenticated() = _Unauthenticated;
}

Now I have this on my UI depending on the state of my app. I want to render different views.

    return state.when(
      initial: () => _buildInitial(context),
      authenticated: (user) => _buildAuthenticated(),
      unauthenticated: () => _buildUnauthenticated(),
    );

I’m getting the following error on my bloc.

This line right here is triggering the error.

I’m using the freezed package to generate Union, and using Bloc 8.0.

Solution

I have a solution/workaround for this case.
Let’s make an (for example) AuthEvent.onUserDataUpdated(User) event, in the stream listener you have to call add() with this event and create a handler for it (on<…>(…)) to emit new AuthState.

Answered By – jkirtyan

Answer Checked By – Terry (FlutterFixes Volunteer)