错误：类型参数“RoutesBloc”不符合“BlocBuilder”上类型变量“B”的绑定“BlocBase<S>”

Question

我收到了这个错误，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('...');
      },
    );
  }
}

完全错误：

lib/screens/home_screen.dart:86:12：错误：类型参数“RoutesBloc”不符合“BlocBuilder”上类型变量“B”的绑定“BlocBase”。

• “RoutesBloc”来自“/blocs/routes/routes_bloc.dart”（“lib/blocs/routes/routes_bloc.dart”）。
• 'BlocBase' 来自'package:bloc/src/bloc.dart' ('../../AppData/Local/Pub/Cache/hosted/pub.dartlang.org/bloc-7.0.0/lib /src/bloc.dart'）。 尝试更改类型参数，使它们符合界限。 返回 BlocBuilder( ^

我在main.dart 中使用multiplocprovider，如下所示：

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 最终会出现同样的错误。

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
   }
 )