扑动：未处理的异常：错误状态：调用关闭后无法添加新事件

Question

我正在尝试使用 bloc 模式来管理来自 API 的数据并在我的小部件中显示它们。我能够从 API 获取数据并处理并显示它，但我使用的是底部导航栏，当我更改选项卡并转到上一个选项卡时，它 returns 此错误：

Unhandled Exception: Bad state: Cannot add new events after calling close.

我知道这是因为我正在关闭流然后尝试添加到它，但我不知道如何修复它，因为不处理 publishsubject 将导致 memory leak。这是我的 Ui 代码：

class CategoryPage extends StatefulWidget {
  @override
  _CategoryPageState createState() => _CategoryPageState();
}

class _CategoryPageState extends State<CategoryPage> {
  @override
  void initState() {
    serviceBloc.getAllServices();
    super.initState();
  }

  @override
  void dispose() {
    serviceBloc.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return StreamBuilder(
      stream: serviceBloc.allServices,
      builder: (context, AsyncSnapshot<ServiceModel> snapshot) {
        if (snapshot.hasData) {
          return _homeBody(context, snapshot);
        }
        if (snapshot.hasError) {
          return Center(
            child: Text('Failed to load data'),
          );
        }
        return CircularProgressIndicator();
      },
    );
  }
}

_homeBody(BuildContext context, AsyncSnapshot<ServiceModel> snapshot) {
  return Stack(
      Padding(
          padding: EdgeInsets.only(top: screenAwareSize(400, context)),
          child: _buildCategories(context, snapshot))
    ],
  );
}

_buildCategories(BuildContext context, AsyncSnapshot<ServiceModel> snapshot) {
  return Padding(
    padding: EdgeInsets.symmetric(vertical: 20),
    child: GridView.builder(
      gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
          crossAxisCount: 3, crossAxisSpacing: 3.0),
      itemCount: snapshot.data.result.length,
      itemBuilder: (BuildContext context, int index) {
        return InkWell(
          child: CategoryWidget(
            title: snapshot.data.result[index].name,
            icon: Icons.phone_iphone,
          ),
          onTap: () {},
        );
      },
    ),
  );
}

这是我的集团代码：

class ServiceBloc extends MainBloc {
  final _repo = new Repo();
  final PublishSubject<ServiceModel> _serviceController =
      new PublishSubject<ServiceModel>();
  Observable<ServiceModel> get allServices => _serviceController.stream;
  getAllServices() async {
    appIsLoading();
    ServiceModel movieItem = await _repo.getAllServices();
    _serviceController.sink.add(movieItem);
    appIsNotLoading();
  }

  void dispose() {
    _serviceController.close();
  }
}

ServiceBloc serviceBloc = new ServiceBloc();

我没有包括 repo 和 API 代码，因为它不在这个错误的主题中。

Answer 1

如果错误实际上是由您发布的代码引起的，我将添加一个检查以确保在调用 dispose() 后没有添加新事件。

class ServiceBloc extends MainBloc {
  final _repo = new Repo();
  final PublishSubject<ServiceModel> _serviceController =
      new PublishSubject<ServiceModel>();
  Observable<ServiceModel> get allServices => _serviceController.stream;
  getAllServices() async {
    // do nothing if already disposed
    if(_isDisposed) {
      return;
    }
    appIsLoading();
    ServiceModel movieItem = await _repo.getAllServices();
    _serviceController.sink.add(movieItem);
    appIsNotLoading();
  }

  bool _isDisposed = false;
  void dispose() {
    _serviceController.close();
    _isDisposed = true;
  }
}

ServiceBloc serviceBloc = new ServiceBloc();

Answer 2

使用StreamController.isClosed检查控制器是否关闭，如果没有关闭则添加数据。

if (!_controller.isClosed) 
  _controller.sink.add(...); // safe to add data as _controller isn't closed yet

来自文档：

Whether the stream controller is closed for adding more events.

The controller becomes closed by calling the close method. New events cannot be added, by calling add or addError, to a closed controller.

If the controller is closed, the "done" event might not have been delivered yet, but it has been scheduled, and it is too late to add more events.

Answer 3

我运行遇到同样的错误并注意到如果您检查 isClosed，则屏幕不会更新。在您的代码中，您必须从 Bloc 文件中删除最后一行：

ServiceBloc serviceBloc = new ServiceBloc();

并将此行放在 CategoryPage 中的 initState() 之前。通过这种方式，您的小部件正在创建和处置集团。之前，widget 仅处理 bloc，但在重新创建 widget 时永远不会重新创建它。

Answer 4

@cwhisperer 完全正确。像下面一样在小部件中初始化和处理你的块。

final ServiceBloc serviceBloc = new ServiceBloc();

  @override
  void initState() {
    serviceBloc.getAllServices();
    super.initState();
  }

  @override
  void dispose() {
    serviceBloc.dispose();
    super.dispose();
  }

并从您的 class ServiceBloc

中删除 ServiceBloc serviceBloc = new ServiceBloc();

Answer 5

除了提供的解决方案外，我认为您还应该排空 ServiceBloc 中使用的流 allServices：

@override
void dispose() {
      ...
      allServices?.drain(); 
}

Answer 6

ServiceBloc serviceBloc = new ServiceBloc();

// 删除这段代码 // 不要在同一个页面中初始化 class 会导致状态不佳。

Answer 7

我在生产中也遇到了这个问题，我意识到我们应该在处置 Widget 时处置 BehaviorSubject（或任何其他 StreamController），或者在添加新值之前检查 Stream 是否关闭。

这是一个很好的扩展来完成所有工作：

extension BehaviorSubjectExtensions <T> on BehaviorSubject<T> {
  set safeValue(T newValue) => isClosed == false ? add(newValue) : () {};
}

你可以这样使用它：

class MyBloc {
  final _data = BehaviorSubject<String>();
  
  void fetchData() {
    // get your data from wherever it is located
    _data.safeValue = 'Safe to add data';
  }

  void dispose() {
    _data.close();
  }
}

如何在Widget中配置：

class CategoryPage extends StatefulWidget {
  @override
  _CategoryPageState createState() => _CategoryPageState();
}

class _CategoryPageState extends State<CategoryPage> {
  late MyBloc bloc;

  @override
  void initState() {
    bloc = MyBloc();
    bloc.fetchData();
    super.initState();
  }

  @override
  void dispose() {
    bloc.dispose();
    super.dispose();
  }

  // Other part of your Widget
}

Answer 8

更好的是，如果您不确定在处理后不会重用该流：

call the drain() function on the stream before closing the stream.

dispose() async{
await _coinDataFetcher.drain();
_coinDataFetcher.close();
_isdisposed = true;

}

扑动：未处理的异常：错误状态：调用关闭后无法添加新事件

flutter: Unhandled Exception: Bad state: Cannot add new events after calling close

dart

flutter

bloc