扑 returns "No ancestor could be found starting from the context that was passed to I/flutter"

Question

我不知道这段代码有什么问题。此页面上有一个 bloc 提供商：

Widget build(BuildContext context) {
return MultiBlocProvider(
  providers: [
    BlocProvider(
      create: (BuildContext context) {
        return DatabaseBloc();
      },
    ),
    BlocProvider(
      create: (BuildContext context) {
        return QuestionholderBloc();
      },
    )
  ],`child:RaisedButton(
                  splashColor: Colors.green[600],
                  focusElevation: 50.0,
                  hoverElevation: 50.0,
                  color: Colors.green[600],
                  shape: RoundedRectangleBorder(
                      side: BorderSide(color: Colors.yellow[700]),
                      borderRadius: BorderRadius.circular(50.0)),
                  child: Text(
                    "Start",
                    style: TextStyle(fontWeight: FontWeight.bold),
                  ),
                  textColor: Colors.white70,
                  onPressed: () {
                    ExtendedNavigator.of(context)
                        .pushNamed(Routes.questionHandler);
                  }),)

对于可能出现的语法错误，我们深表歉意。在 QuestionHolderPage 我有：

 void didChangeDependencies() {
_statusbloc = BlocProvider.of<QuestionholderBloc>(context);
_dbbloc = BlocProvider.of<DatabaseBloc>(context);
_statusbloc.add(CheckStatus());
super.didChangeDependencies();
}

 Widget build(BuildContext context) {
return Scaffold(
  body: MultiBlocListener(
    listeners: [
      BlocListener<QuestionholderBloc, QuestionholderState>(
        listener: (context, state) {
          if (state is NoQuestions) {
            _dbbloc.add(GetQuestions());
          } else if (state is HasQuestions) {
            _statusbloc.add(GetQuestion());
          }
        },
      ),
      BlocListener<DatabaseBloc, DatabaseState>(
        listener: (context, state) {
          if (state is Loaded) {
            _statusbloc.add(SetQuestions(questionsToSet: state.questions));
          }
        },
      ),
    ],
    child: BlocBuilder<QuestionholderBloc, QuestionholderState>(
      builder: (context, state) {
        if (state is QuestionLoaded) {
          return QuestionWidget(question: state.question);
        } else {
          return CircularProgressIndicator();
        }
      },
    ),
  ),
);
}
}

错误：

Error: No ancestor could be found starting from the context that was passed to I/flutter ( 4318): BlocProvider.of().

Answer 1

从您的代码中可以看出，您正在从初始化 MultiBlocProvider 的位置导航，因此您会收到此错误。

如果您在一个屏幕中初始化并在导航到其他屏幕后访问它，您将无法访问提供程序。

第一种解决方法

如果你想这样做，那么可以在 MaterialApp 小部件上面初始化你的 MultiBlocProvider，这样你就可以在你的应用程序的每个屏幕上访问。

第二种方式：

您可以在导航时传递要在其他屏幕中访问的所有值，并在该屏幕中初始化新的 MultiBlocProvider。

扑 returns "No ancestor could be found starting from the context that was passed to I/flutter"

Flutter returns "No ancestor could be found starting from the context that was passed to I/flutter"

dart

flutter

bloc

flutter-bloc