Error: Type argument 'RoutesBloc' doesn't conform to the bound 'BlocBase<S>' of the type variable 'B' on 'BlocBuilder'

Question

我遇到了这个错误，但我不知道它是从哪里来的。

class Routes extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return BlocBuilder<RoutesBloc, RoutesEvent>( // <-- It occurs here
      builder: (context, state) {
        return Text('...');
      },
    );
  }
}

完整错误：

lib/screens/home_screen.dart:86:12: Error: Type argument 'RoutesBloc' doesn't conform to the bound 'BlocBase' of the type variable 'B' on 'BlocBuilder'.

'RoutesBloc' is from '/blocs/routes/routes_bloc.dart' ('lib/blocs/routes/routes_bloc.dart').

'BlocBase' is from 'package:bloc/src/bloc.dart' ('../../AppData/Local/Pub/Cache/hosted/pub.dartlang.org/bloc-7.0.0/lib/src/bloc.dart'). Try changing type arguments so that they conform to the bounds. return BlocBuilder<RoutesBloc, RoutesEvent>( ^

我在 main.dart 中使用 multiplocprovider 是这样的：

MultiBlocProvider(
  providers: [
      ...,
      BlocProvider<RoutesBloc>(
          create: (_) => RoutesBloc(
            apiRepository: ApiRepository.create(),
          )..add(RoutesLoaded()),
        ),
      ],
  child: AppView(),
)

routes_state.dart:

abstract class RoutesState extends Equatable {

const RoutesState();

  @override
  List<Object> get props => [];
}

class RoutesLoadInProgress extends RoutesState {}

class RoutesLoadSuccess extends RoutesState {
  final List<BoulderingRoute> routes;

  const RoutesLoadSuccess([this.routes = const []]);

  @override
  List<Object> get props => [routes];
}

class RoutesLoadFailure extends RoutesState {}

routes_event.dart:

abstract class RoutesEvent extends Equatable {
  const RoutesEvent();

  @override
  List<Object> get props => [];
}

class RoutesLoaded extends RoutesEvent {}

class RouteAdded extends RoutesEvent {
  final BoulderingRoute route;

  const RouteAdded({this.route}) : assert(route != null);

  @override
  List<Object> get props => [route];
}

class RouteUpdated extends RoutesEvent {
  final BoulderingRoute route;

  const RouteUpdated({this.route}) : assert(route != null);

  @override
  List<Object> get props => [route];
}

class RouteDeleted extends RoutesEvent {
  final BoulderingRoute route;

  const RouteDeleted({this.route}) : assert(route != null);

  @override
  List<Object> get props => [route];
}

routes_bloc.dart:

class RoutesBloc extends Bloc<RoutesEvent, RoutesState> {
  final ApiRepository _apiRepository;

  RoutesBloc({ApiRepository apiRepository})
      : assert(apiRepository != null),
        this._apiRepository = apiRepository,
        super(RoutesLoadInProgress());

  @override
  Stream<RoutesState> mapEventToState(
    RoutesEvent event,
  ) async* {
    print(event);
    if (event is RoutesLoaded) {
      yield* _mapRoutesLoadedToState();
    }
  }

  Stream<RoutesState> _mapRoutesLoadedToState() async* {
    try {
      print('start');
      final List<BoulderingRoute> routes =
          await _apiRepository.fetchBoulderingRoutes();
      yield RoutesLoadSuccess(routes);
    } catch (_) {
      yield RoutesLoadFailure();
    }
  }
}

我首先认为我的 RoutesBloc 一定有问题，但是将 blocbuilder 更改为我在另一个地方成功使用的 bloc 最终得到了相同的结果错误。

有人知道这是从哪里来的吗？

Answer 1

应该是return BlocBuilder<RoutesBloc, RoutesState> 检查这个：https://pub.dev/packages/flutter_bloc#blocbuilder

 BlocBuilder<BlocA, BlocAState>(
   builder: (context, state) {
     // return widget here based on BlocA's state
   }
 )

Error: Type argument 'RoutesBloc' doesn't conform to the bound 'BlocBase<S>' of the type variable 'B' on 'BlocBuilder'

Error: Type argument 'RoutesBloc' doesn't conform to the bound 'BlocBase<S>' of the type variable 'B' on 'BlocBuilder'

state-management

dart

flutter

bloc

flutter-bloc