Flutter：未处理的异常：错误状态：调用关闭后无法添加新事件

我试图使用bloc模式来管理API中的数据，并在我的小部件中显示它们.我可以从API中获取数据并进行处理和显示，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，它会返回以下错误:

未处理的异常:状态错误:调用后无法添加新事件 关.

我知道这是因为我正在关闭流，然后try 添加它，但我不知道如何修复它，因为不处理publishsubject将导致memory leak. 这是我的用户界面代码:

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: () {},
        );
      },
    ),
  );
}

以下是我的区块代码:

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，因为它不在此错误的主题中.