关于依赖注入：即使事件被重新触发，Flutter BlocListener 也只执行一次

Flutter BlocListener executed only once even after event gets re-fired

我正在 Flutter 中实现 Reso Coder 的简洁架构。我按照他的指南将项目划分为层并使用依赖注入。在其中一种情况下，我希望有以下场景：管理员用户登录，在其主屏幕上查看数据，对其进行编辑，然后按一个按钮，将数据保存到本地数据库 (sqflite)。保存数据后，我想显示一个带有某种文本的 Snackbar ，例如"设置已保存！"。这是我的代码(部分)：

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class AdministratorPage extends StatefulWidget {
@override
_AdministratorPageState createState() => _AdministratorPageState();
}

class _AdministratorPageState extends State<AdministratorPage> {
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
backgroundColor: Theme.of(context).backgroundColor,
centerTitle: true,
leading: Container(),
title: Text(AppLocalizations.of(context).translate('adminHomeScreen')),
),
body: SingleChildScrollView(
child: buildBody(context),
),
);
}

BlocProvider<SettingsBloc> buildBody(BuildContext context) {
return BlocProvider(
create: (_) => serviceLocator<SettingsBloc>(),
child: BlocListener<SettingsBloc, SettingsState>(
listener: (context, state) {
if (state is SettingsUpdatedState) {
Scaffold.of(context).showSnackBar(
SnackBar(
content: Text(
AppLocalizations.of(context).translate('settingsUpdated')),
backgroundColor: Colors.blue,
),
);
}
},
child: Column(
children: <Widget>[
SizedBox(
height: 20.0,
),
AdministratorInput(),
SizedBox(
width: double.infinity,
child: RaisedButton(
child: Text('LOG OUT'),
onPressed: () {
serviceLocator<AuthenticationBloc>().add(LoggedOutEvent());
Routes.sailor(Routes.loginScreen);
},
),
),
],
),
),
);
}
}

这是 AdministratorInput 小部件：

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class AdministratorInput extends StatefulWidget {
@override
_AdministratorInputState createState() => _AdministratorInputState();
}

class _AdministratorInputState extends State<AdministratorInput> {
String serverAddress;
String daysBack;
final serverAddressController = TextEditingController();
final daysBackController = TextEditingController();

@override
Widget build(BuildContext context) {
return Center(
child: Padding(
padding: const EdgeInsets.all(10.0),
child: BlocBuilder<SettingsBloc, SettingsState>(
builder: (context, state) {
if (state is SettingsInitialState) {
BlocProvider.of<SettingsBloc>(context)
.add(SettingsPageLoadedEvent());
} else if (state is SettingsFetchedState) {
serverAddressController.text =
serverAddress = state.settings.serverAddress;
daysBackController.text =
daysBack = state.settings.daysBack.toString();
}

return Column(
children: <Widget>[
Container(
child: Row(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text(AppLocalizations.of(context)
.translate('serverAddress')),
],
),
),
Container(
height: 40.0,
child: TextField(
controller: serverAddressController,
decoration: InputDecoration(
border: OutlineInputBorder(),
),
onChanged: (value) {
serverAddress = value;
},
),
),
SizedBox(
height: 5.0,
),
// Days Back Text Field
Container(
child: Row(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Text(AppLocalizations.of(context).translate('daysBack')),
],
),
),
Container(
height: 40.0,
child: TextField(
controller: daysBackController,
decoration: InputDecoration(
border: OutlineInputBorder(),
),
onChanged: (value) {
daysBack = value;
},
),
),
SizedBox(
width: double.infinity,
child: RaisedButton(
child: Text('SAVE CHANGES'),
onPressed: updatePressed,
),
),
SizedBox(
width: double.infinity,
child: RaisedButton(
child: Text('REFRESH'),
onPressed: refreshPressed,
),
),
],
);
},
),
),
);
}

void updatePressed() {
BlocProvider.of<SettingsBloc>(context).add(
SettingsUpdateButtonPressedEvent(
settings: SettingsAggregate(
serverAddress: serverAddress,
daysBack: int.parse(daysBack),
),
),
);
}

void refreshPressed() {
BlocProvider.of<SettingsBloc>(context).add(
SettingsRefreshButtonPressedEvent(),
);
}
}

SettingsBloc 是一个标准的 bloc 模式，带有事件和状态以及一个映射器方法。它是使用 get_it 包注入的。这是实例化的方式：

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serviceLocator.registerFactory(
() => SettingsBloc(
pullUsersFromServerCommand: serviceLocator(),
getSettingsQuery: serviceLocator(),
updateSettingsCommand: serviceLocator(),
),
);

命令的所有实例和对 bloc 构造函数的查询都以相同的方式正确实例化。

这里是集团：

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class SettingsBloc extends Bloc<SettingsEvent, SettingsState> {
final PullUsersFromServerCommand pullUsersFromServerCommand;
final UpdateSettingsCommand updateSettingsCommand;
final GetSettingsQuery getSettingsQuery;

SettingsBloc({
@required PullUsersFromServerCommand pullUsersFromServerCommand,
@required UpdateSettingsCommand updateSettingsCommand,
@required GetSettingsQuery getSettingsQuery,
}) : assert(pullUsersFromServerCommand != null),
assert(updateSettingsCommand != null),
assert(getSettingsQuery != null),
pullUsersFromServerCommand = pullUsersFromServerCommand,
updateSettingsCommand = updateSettingsCommand,
getSettingsQuery = getSettingsQuery;

@override
SettingsState get initialState => SettingsInitialState();

@override
Stream<SettingsState> mapEventToState(SettingsEvent event) async* {
if (event is SettingsPageLoadedEvent) {
final getSettingsEither = await getSettingsQuery(NoQueryParams());

yield* getSettingsEither.fold((failure) async* {
yield SettingsFetchedFailureState(error:"settingsDatabaseError");
}, (result) async* {
if (result != null) {
yield SettingsFetchedState(settings: result);
} else {
yield SettingsFetchedFailureState(
error:"settingsFetchFromDatabaseError");
}
});
} else if (event is SettingsUpdateButtonPressedEvent) {
final updateSettingsEither = await updateSettingsCommand(
UpdateSettingsParams(settingsAggregate: event.settings));

yield* updateSettingsEither.fold((failure) async* {
yield SettingsUpdatedFailureState(error:"settingsDatabaseError");
}, (result) async* {
if (result != null) {
yield SettingsUpdatedState();
} else {
yield SettingsUpdatedFailureState(
error:"settingsUpdateToDatabaseError");
}
});
} else if (event is SettingsRefreshButtonPressedEvent) {
final pullUsersFromServerEither =
await pullUsersFromServerCommand(NoCommandParams());

yield* pullUsersFromServerEither.fold((failure) async* {
yield SettingsRefreshedFailureState(
error:"settingsRefreshDatabaseError");
}, (result) async* {
if (result != null) {
yield SettingsUpdatedState();
} else {
yield SettingsRefreshedFailureState(error:"settingsRefreshedError");
}
});
}
}
}

当我第一次进入这个屏幕时，一切都很完美。数据是从数据库中获取的，加载到屏幕上，如果我更改它并按 SAVE，它会显示 Snackbar。我的问题是如果我想在停留在该屏幕上时再次编辑数据。我再次编辑它，因此触发更改事件，bloc 获取它，调用下面的正确命令并将数据保存在数据库中。然后更改 bloc 的状态以试图告诉 UI，"嘿，我有一个新状态，使用它"。但是 BlocListener 再也不会被调用了。

我应该如何实现我想要的行为？

编辑：
我在登录用户的应用程序中添加了我之前使用的另一个块。登录页面使用了该块，并且在错误的用户名或密码时，我显示了一个快餐栏，清除输入字段并让页面准备好更多。如果我使用错误的凭据重试，我可以再次看到小吃栏。

这里是登录块：

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class LoginBloc extends Bloc<LoginEvent, LoginState> {
final AuthenticateUserCommand authenticateUserCommand;
final AuthenticationBloc authenticationBloc;

LoginBloc({
@required AuthenticateUserCommand authenticateUserCommand,
@required AuthenticationBloc authenticationBloc,
}) : assert(authenticateUserCommand != null),
assert(authenticationBloc != null),
authenticateUserCommand = authenticateUserCommand,
authenticationBloc = authenticationBloc;

@override
LoginState get initialState => LoginInitialState();

@override
Stream<LoginState> mapEventToState(LoginEvent event) async* {
if (event is LoginButtonPressedEvent) {
yield LoginLoadingState();

final authenticateUserEither = await authenticateUserCommand(
AuthenticateUserParams(
username: event.username, password: event.password));

yield* authenticateUserEither.fold((failure) async* {
yield LoginFailureState(error:"loginDatabaseError");
}, (result) async* {
if (result != null) {
authenticationBloc.add(LoggedInEvent(token: result));
yield LoginLoggedInState(result);
} else {
yield LoginFailureState(error:"loginUsernamePasswordError");
}
});
}
}
}

这里的 Event 和 State 类扩展了 Equatable。而且由于它按照预期工作，我在"设置"页面中以同样的方式进行了操作(失败的地方)。在 UI 中，我根据需要多次提高 LoginButtonPressedEvent 并分别调用 BlocListener。