我是Flutter的新手,也是Bloc使用的新手。
我在编译代码时遇到错误:
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)
我试图改变我的集团课程中的一些东西,但没有任何作用。
这是我的博客课:
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:'(
在面对这个问题一段时间后,我希望本文能帮助您更多地了解context
。一般解决方案与@Filled Stacks的答案相同。这意味着您在导航到新页面时必须传递集团,以便BlocProvider
可以找到您将收到哪种类型的集团。
我建议启动整个应用程序的 main 函数,它将通过屏幕初始化您的屏幕和上下文。例如:
- 初始化和传递集团:
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);
}
请参阅此处的示例应用程序:https://github.com/huynguyennovem/flutter_todo
下面的行是你的问题。错误正是消息所说的。
...
child: BlocBuilder<BtnEvent, BtnState>(
bloc: BlocProvider.of<BtnBloc>(context), <------- Problem line
builder: (context, BtnState state) {
...
您在那里使用的上下文没有附加BlocBuilder,因此没有任何内容将BloC从顶部传递到您的LoginState。你可以
- 使用现有集团 (_btnBloc( 并将其传入(推荐(
- 包装小部件,将 LoginState 放在屏幕上,并使用 BlocProvider 进行访问,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。
改变
bloc: BlocProvider.of<BtnBloc>(context), <------- Problem line
自
bloc: _btnBloc