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

Posted 2023-02-23

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

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

【发布时间】：2021-07-29 04:17:35

【问题描述】：

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？

【参考方案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
   
 )

【讨论】：

我对自己的愚蠢印象深刻。我一遍又一遍地看了这个，但没有看到明显的：/。谢谢@Luis A. Chaglla。