Question

我是Flutter的新手，也是Bloc使用的新手。

编译代码时出现错误：

    The following assertion was thrown building Login(dirty, state: _LoginFormState#44e7f):
         BlocProvider.of() called with a context that does not contain a Bloc of type BtnBloc.
         No ancestor could be found starting from the context that was passed to
         BlocProvider.of<BtnBloc>().
       This can happen if the context you use comes from a widget above the BlocProvider.
         This can also happen if you used BlocProviderTree and didn't explicity provide 
         the BlocProvider types: BlocProvider(bloc: BtnBloc()) instead of BlocProvider<BtnBloc>(bloc:
         BtnBloc()).
         The context used was: Login(dirty, state: _LoginFormState#44e7f)

我试图更改我的bloc类中的某些内容，但是对此没有任何作用。

这是我的博客课程：

class BtnBloc extends Bloc<BtnEvent, BtnState> {
  @override
  BtnState get initialState => BtnState.initial();

  @override
  Stream<BtnState> mapEventToState(
      BtnState currentState, BtnEvent event) async* {
    if (event is IdleEvent) {
      yield currentState..state = 1;
    } else if (event is LoadingEvent) {
      yield currentState..state = 1;
    } else if (event is RevealEvent) {
      yield currentState..state = 2;
    }
  }
}

这是我的构建方法：

final _btnBloc = new BtnBloc();

  _LoginFormState(
      {Key key,
      this.primaryColor,
      this.backgroundColor,
      this.backgroundImage,
      this.logo});

  @override
  Widget build(BuildContext context) {
    return BlocProvider(
        bloc: _btnBloc,
        child: BlocBuilder<BtnEvent, BtnState>(
            bloc: BlocProvider.of<BtnBloc>(context),
            builder: (context, BtnState state) {
return myWidget();

请帮助我：'（

Answer 1

经过一段时间后，我希望this article将帮助您更多地了解context。通用解决方案与@Filled Stacks的答案相同。这意味着导航到新页面时必须pass the bloc，以便BlocProvider可以找到将接收到哪种类型的Bloc。

我建议为整个应用程序初始化主要功能，该功能将初始化您的屏幕和整个屏幕的上下文。例如：

初始化并通过Bloc：

class ListTodoPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return BlocProvider<TodoBloc>(
        create: (context) => TodoBloc(TodoDao())..add(QueryTodoEvent()),
        child: ListTodoPageful());
  }
}

class ListTodoPageful extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return ListTodoState();
  }
}

class ListTodoState extends State<ListTodoPageful> {
  TodoBloc _todoBloc;
  @override
  Widget build(BuildContext context) {
    _todoBloc = BlocProvider.of<TodoBloc>(
        context);
   //...
   floatingActionButton: FloatingActionButton(
        onPressed: () {
          Navigator.push(
              context,
              CupertinoPageRoute(
                  builder: (context) => BlocProvider.value(
                      value: _todoBloc, child: CreateTaskPage())));
        }
  //...
}

接收集团：

class _CreatePageState extends State<CreateTaskPage> {
  TodoBloc _todoBloc;

  @override
  Widget build(BuildContext context) {
    _todoBloc = BlocProvider.of<TodoBloc>(context);
}

在这里参考我的示例应用程序：https://github.com/huynguyennovem/flutter_todo

Answer 2

下面的行是您的问题。该错误正是消息所显示的内容。

...
child: BlocBuilder<BtnEvent, BtnState>(
     bloc: BlocProvider.of<BtnBloc>(context), <------- Problem line
     builder: (context, BtnState state) {
...

您在此处使用的上下文没有附加BlocBuilder，因此没有东西将BloC从顶部向下传递到LoginState。您可以

使用您现有的集团（_btnBloc）并将其传递给（推荐）
包装小部件，将BlogProvider放在LoginState屏幕上，以便您可以在小部件状态下访问它。

如果这是您的第一个视图，请使用1。

更改

 bloc: BlocProvider.of<BtnBloc>(context), <------- Problem line

收件人

bloc: _btnBloc

Flutter Bloc：从上下文开始找不到祖先吗？

2 个答案: