BLoC 产生新状态后 BlocBuilder() 未更新

Question

我是 flutter 上的 BLoC 模式的新手，我正在尝试使用它重建一个凌乱的 flutter 应用程序。目前，我打算获取用户应用程序列表并使用 ListView.builder() 显示它们。问题是每当我的 AppsBloc 的状态发生变化时，我的 StatelessWidget 都不会更新以显示新状态。我试过：

使用 main.dart 中的 MultiBlocProvider() 而不是将此 appsBloc 嵌套在包含整个应用程序的 themeBloc 中
返回列表而不是地图，即使我的辅助方法 returns 是正确的地图
使用 StatefulWidget，仅在 ListView 上使用 BlocProvider()...

我一直在阅读有关类似项目的这个问题，问题可能出在 Equatable 上。但是，由于我也是 Equatable 的新手，因此我无法识别出任何错误。我一直在 VScode 上调试项目，在 yield* 行设置断点，似乎没问题。尽管如此，小部件并没有得到重建：它一直显示对应于 InitialState 的文本。

此外，BLoC 不会在控制台上打印任何内容，即使所有状态都已覆盖 toString()

这些是我的 3 个 BLoC 文件：

apps_bloc.dart

import 'dart:async';

import 'package:bloc/bloc.dart';
import 'package:device_apps/device_apps.dart';
import 'package:equatable/equatable.dart';

part 'apps_event.dart';
part 'apps_state.dart';

class AppsBloc extends Bloc<AppsEvent, AppsState> {
  @override
  AppsState get initialState => AppsInitial();

  @override
  Stream<AppsState> mapEventToState(AppsEvent event) async* {
    yield AppsLoadInProgress();
    if (event is AppsLoadRequest) {
      yield* _mapAppsLoadSuccessToState();
      }
  }

  Stream<AppsState> _mapAppsLoadSuccessToState() async* {
    try {
      final allApps = await DeviceApps.getInstalledApplications(
          onlyAppsWithLaunchIntent: true, includeSystemApps: true);

      final listaApps = allApps
        ..sort((a, b) =>
            a.appName.toLowerCase().compareTo(b.appName.toLowerCase()));

      final Map<Application, bool> res =
          Map.fromIterable(listaApps, value: (e) => false);

      yield AppsLoadSuccess(res);
    } catch (_) {
      yield AppsLoadFailure();
    }
  }
}

apps_event.dart

part of 'apps_bloc.dart';

abstract class AppsEvent extends Equatable {
  const AppsEvent();

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

class AppsLoadRequest extends AppsEvent {}

apps_state.dart

part of 'apps_bloc.dart';

abstract class AppsState extends Equatable {
  const AppsState();

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

class AppsInitial extends AppsState {
  @override
  String toString() => "State: AppInitial";
}

class AppsLoadInProgress extends AppsState {
  @override
  String toString() => "State: AppLoadInProgress";
}

class AppsLoadSuccess extends AppsState {
  final Map<Application, bool> allApps;
  const AppsLoadSuccess(this.allApps);

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

  @override
  String toString() => "State: AppLoadSuccess, ${allApps.length} entries";
}

class AppsLoadFailure extends AppsState {
  @override
  String toString() => "State: AppLoadFailure";
}

main_screen.dart

class MainScreen extends StatelessWidget {
  const MainScreen({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return TabBarView(
        children: <Widget>[
          HomeScreen(),
          BlocProvider(
            create: (BuildContext context) => AppsBloc(),
            child: AppsScreen(),
          )
          ,
        ],
      );
  }
}

apps_screen.dart

class AppsScreen extends StatelessWidget {
  const AppsScreen({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
          body: Container(
          margin: EdgeInsets.fromLTRB(30, 5, 10, 0),
          child: Column(children: <Widget>[
            Row(
              children: <Widget>[
                Text("Apps"),
              ],
            ),
            Row(children: <Widget>[
              Container(
                width: MediaQuery.of(context).size.width - 50,
                height: MediaQuery.of(context).size.height - 150,
                child: BlocBuilder<AppsBloc, AppsState>(
                  builder: (BuildContext context, AppsState state) {
                    if (state is AppsLoadSuccess)
                      return Text("LOADED");
                    else if (state is AppsInitial)
                      return GestureDetector(
                          onTap: () => AppsBloc().add(AppsLoadRequest()),
                          child: Text("INITIAL"));
                    else if (state is AppsLoadInProgress)
                      return Text("LOADING...");
                    else if (state is AppsLoadFailure)
                      return Text("LOADING FAILED");
                  },
                ),
              ),
            ])
          ])),
    );
  }
}

Answer 1

在GestureDetector.onTap()中你创建了一个新的AppsBloc()，这是错误的。所以，你需要：

apps_screen.dart:

  AppsBloc _appsBloc;

  @override
  void initState() {
    super.initState();

    _appsBloc = BlocProvider.of<AppsBloc>(context);
  }

//...

  @override
  Widget build(BuildContext context) {
    //...
    return GestureDetector(
      onTap: () => _appsBloc.add(AppsLoadRequest()),
      child: Text("INITIAL")
    );
    //...
  }

或者即使没有 _appsBloc 字段，您也可以这样做：

BlocProvider.of<AppsBloc>(context).add(AppsLoadRequest())

BLoC 产生新状态后 BlocBuilder() 未更新

BlocBuilder() not being updated after BLoC yielding new state

dart

flutter

bloc