Question

这是我的 Flutter 应用程序 MultiBlocProvider 设置；

MultiBlocProvider(
      providers: [
        BlocProvider<LocationBloc>(create: (BuildContext context) {
          return LocationBloc();
        }),

        BlocProvider<AddressBloc>(create: (BuildContext context) {
          return AddressBloc(
              location: BlocProvider.of<LocationBloc>(context)
                ..add(LocationStarted()))
            ..add(AddressStarted());
        }),

        BlocProvider<CampaignBloc>(
          create: (BuildContext context) => CampaignBloc(
              addressBloc: BlocProvider.of<AddressBloc>(context),
              repo: CampaignsRepository())
            ..add(CampaignsInitial()),
        ),

        BlocProvider<BusinessBloc>(
          create: (BuildContext context) => BusinessBloc(
              addressBloc: BlocProvider.of<AddressBloc>(context),
              repo: BusinessRepository())
            ..add(BusinessInitial()),
        )
      ],
      child: MaterialApp(...)
          ,
    )

LocationBloc 从定位服务中获取位置。 AddressBloc 从 LocationBloc 获取更新的位置并将其转换为地址。

CampaignBloc 在其构造函数中侦听 AddressBloc 流以获取地址（位置）更改，并针对更改的位置发出广告系列。

CampaignBloc({required this.repo, required this.addressBloc})
      : super(CampaignState()) {
    _addressSubscription =
        addressBloc.stream.asBroadcastStream().listen((AddressState state) {
      if (state is AddressLoadSuccess) {
        Location location = state.location;

        add(CampaignChangedLocation(location: location));
      }
    });
  }

BusinessBloc 在它的构造函数中做同样的事情，并且（应该）为改变的位置发出业务。

 BusinessBloc({required this.repo, required this.addressBloc})
      : super(BusinessInitial()) {
    _addressSubscription =
        addressBloc.stream.asBroadcastStream().listen((AddressState state) {
      if (state is AddressLoadSuccess) {
        Location location = state.location;

        add(BusinessChangedLocation(location: location));
      }
    });
  }

HomeView 有一个 BlocBuilder 来构建活动列表。

AlliesView 有一个 BlocBuilder 来构建企业列表。

CampaignBloc 在构建 HomeView 时正在接收更新的位置，但在转换到 AlliesView 时，AddressBloc 流上的侦听器没有接收到更新的位置，因为它在事件发生后订阅了流。如何在 AddressBloc 流的后续侦听器中获取更新的位置？

Answer 1

我想出了一个解决方案 - 使用 rxdart 的 ReplaySubject。所以在 AddressBloc 我用

覆盖#stream

  ReplaySubject<AddressState>? s;
  @override
  get stream {
    if (s == null) {
      s = new ReplaySubject<AddressState>();
      Stream upstream = super.stream;
      upstream.listen((value) {
        s!.add(value);
      });
    }
    return s!;
  }

现在，当我创建订阅 AddressBloc 的 BusinessBloc 时，我会在 AddressBloc 流中获得以前的状态。

Answer 2

MultiBlocListener(
  listeners: [
    BlocListener<BlocA, BlocAState>(
      listener: (context, state) {},
    ),
    BlocListener<BlocB, BlocBState>(
      listener: (context, state) {},
    ),
    BlocListener<BlocC, BlocCState>(
      listener: (context, state) {},
    ),
  ],
  child: ChildA(),
)

Flutter Bloc 依赖项的多个侦听器 - 接收以前的状态

2 个答案: