Flutter BLoC mapEventToState仅在事件第一次被调用时，而下次每次触发该事件时都不会被调用 [英] Flutter BLoC mapEventToState gets called only the first time for an event and not called each next time that event is fired
问题描述
我有 Courses 和 Tasks .每个 Course (课程)都有许多 Tasks(任务).这就是为什么我在应用程序中使用不同的屏幕来显示课程列表，并在点击课程后导航到下一个屏幕-任务列表.这是我的课程列表的 onTap 方法:
I have Courses and Tasks. Each Course has many Tasks. That is why I am using different screens in the app to show a list of courses and after a tap on a course, I am navigating to the next screen - a list of tasks. Here is my onTap method of the list of courses:
onTap: () {
TasksPageLoadedEvent pageLoadedEvent =
TasksPageLoadedEvent(
courseId: state.courses[index].id,
truckNumber: this.truckNumber,
);
serviceLocator<TaskBloc>().add(pageLoadedEvent);
Routes.sailor(
Routes.taskScreen,
params: {
Routes.courseNumber:
state.courses[index].courseNumber,
Routes.truckNumber: this.truckNumber,
Routes.courseId: state.courses[index].id,
},
);
}
我创建一个 TasksPageLoadedEvent ，将其传递给 TaskBloc ，然后导航至任务"页面.
I create a TasksPageLoadedEvent, pass it to the TaskBloc and navigate to the Tasks page.
这是 TaskBloc 以及它如何处理映射事件-状态:
Here is the TaskBloc and how it handles the mapping Event - State:
@override
Stream<TaskState> mapEventToState(
TaskEvent event,
) async* {
if (event is TasksLoadingEvent) {
yield TasksLoadingState();
} else if (event is TasksReloadingErrorEvent) {
yield TasksErrorState();
} else if (event is TasksFetchedFailureEvent) {
yield TaskFetchedStateFailureState(error: event.failure);
} else if (event is TasksPulledFromServerEvent) {
yield TasksPulledFromServerState(
truckNumber: event.truckNumber,
courseNumber: event.courseNumber,
courseId: event.courseId,
);
} else if (event is TasksPageLoadedEvent) {
yield TasksLoadingState();
final networkInfoEither = await this.getNetworkInfoQuery(NoQueryParams());
yield* networkInfoEither.fold((failure) async* {
yield TasksErrorState();
}, (success) async* {
if (success) {
final getTasksEither = await getTasksQuery(
GetTasksParams(
truckNumber: event.truckNumber,
courseId: event.courseId,
),
);
yield* getTasksEither.fold((failure) async* {
yield TaskFetchedStateFailureState(error: "coursesDatabaseError");
}, (result) async* {
if (result != null) {
yield TasksFetchedState(tasks: result);
} else {
yield TaskFetchedStateFailureState(
error: "coursesFetchFromDatabaseError");
}
});
} else {
yield TasksNoInternetState();
}
});
}
}
当我导航到任务"页面时， BlocBuilder 检查状态并相应地处理建筑物.我有一个返回"功能，可以导航回到课程"页面:
When I get navigated to the Tasks page, the BlocBuilder checks the state and handles the building accordingly. I have a Go Back functionality that navigates back to the Courses page:
onPressed: () {
serviceLocator<CourseBloc>().add(
CoursesPageLoadedEvent(truckNumber: this.truckNumber),
);
Navigator.of(context).pop(true);
},
这会触发上一页的类似事件，并且会重新加载该事件.
This fires the similar event for the previous page and it gets re-loaded.
如果我想去另一门课程并查看其任务，就会遇到我面临的问题.如果我点击列表中的另一个项目并因此触发一个新的 TasksPageLoadedEvent (具有新属性)，则根本不会调用 mapEventToState().
The problem I am facing happens if I want to go to another course and see its tasks. If I tap on another item in the list and therefore fire a new TasksPageLoadedEvent (with new properties) the mapEventToState() doesn't get called at all.
我以前在BLoC上也遇到过类似的问题，但是他们在讨论 BlocListener 和扩展 Equatable 的状态.这就是为什么我的事件没有扩展 Equatable 的原因(尽管我不确定这是否是这里的问题).但是仍然没有任何反应.
I have had similar issues with BLoC before, but they were regarding the BlocListener and states extending Equatable. That is why I had my events NOT extending Equatable (although I am not sure whether this was the issue here). But still nothing happens.
这是我的活动:
abstract class TaskEvent {
const TaskEvent();
}
class TasksPageLoadedEvent extends TaskEvent {
final String truckNumber;
final int courseId;
TasksPageLoadedEvent({
this.truckNumber,
this.courseId,
});
}
class TasksFetchedFailureEvent extends TaskEvent {
final String failure;
TasksFetchedFailureEvent({
this.failure,
});
}
class TasksLoadingEvent extends TaskEvent {}
class TasksReloadingErrorEvent extends TaskEvent {}
class TasksPulledFromServerEvent extends TaskEvent {
final String courseNumber;
final String truckNumber;
final int courseId;
TasksPulledFromServerEvent({
@required this.courseNumber,
@required this.truckNumber,
@required this.courseId,
});
}
我应该如何在每个页面之间使用两个BLoC来处理我的来回页面?
How should I handle my back-and-forth between the two pages using two BLoCs for each page?
推荐答案
好的，我自己找到了答案！
OK, I found an answer myself!
当然，正如费德里克·乔纳森(Federick Jonathan)所暗示的那样，问题是集团的实例.我正在使用由flutter包get_it创建的单例实例.如果您要实现依赖项注入(例如，用于干净的体系结构)，这真的很有用.
The problem, of course, as Federick Jonathan implied - the instance of the bloc. I am using a singleton instance created by the flutter package get_it. Which is really useful if you are implementing dependency injection (for a clean architecture for example).
所以一个实例就是问题.
So the one instance was the problem.
幸运的是，该程序包已经实现了整洁的方法 resetLazySingleton< T> .
Luckily the package has implemented the neat method resetLazySingleton<T>.
在返回时调用它会重置该小部件中使用的块.因此，当我再次导航到任务"页面时，我正在使用该块的相同实例，但重置了该实例.
Calling it upon going back resets the bloc used in that widget. Therefore when I navigate again to the Tasks page I am working with the same but reset instance of that bloc.
Future<bool> _onWillPop() async {
serviceLocator.resetLazySingleton<TaskBloc>(
instance: serviceLocator<TaskBloc>(),
);
return true;
}
我希望这个答案能够帮助遇到单例，依赖注入以及在带有bloc的Flutter应用程序中来回走动的人.
I hope this answer would help someone in trouble with singletons, dependency injections and going back and forth within a flutter app with bloc.
这篇关于Flutter BLoC mapEventToState仅在事件第一次被调用时，而下次每次触发该事件时都不会被调用的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
