BlocProvider.of() 使用不包含 Bloc<dynamic,dynamic> 类型的 Bloc 的上下文调用

Question

Error: I/flutter ( 5919): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════ I/flutter ( 5919): The following assertion was thrown building Builder: I/flutter ( 5919): BlocProvider.of() called with a context that does not contain a Bloc of type Bloc. I/flutter ( 5919): No ancestor could be found starting from the context that was passed to I/flutter ( 5919): BlocProvider.of>(). I/flutter ( 5919):
This can happen if the context you used comes from a widget above the BlocProvider. I/flutter ( 5919): The context used was: BlocBuilder, dynamic>(dirty, state: I/flutter ( 5919): _BlocBuilderBaseState, dynamic>#55a7d(lifecycle state: created)) I/flutter ( 5919): The relevant error-causing widget was: I/flutter ( 5919): MaterialApp /lib/main.dart:35:12

这是我的主要内容

void main() {
  final StorageRepository storageRepository = StorageRepository();
  final AuthenticationRepository authenticationRepository =
      AuthenticationRepository();
  runApp(BlocProvider<AuthenticationBloc>(
      create: (_) => AuthenticationBloc(
          authenticationRepository: authenticationRepository,
          storageRepository: storageRepository),
      child: MyApp()));
}

MaterialApp 小部件

MaterialApp(
      debugShowCheckedModeBanner: false,
      theme: ThemeData(primarySwatch: Colors.deepPurple),
      home: BlocBuilder(
        builder: (context, state) {
          print(state);
          if (state is Authenticated) {
            return MainPage();
          } else if (state is Unauthenticated) {
            return LoginPage();
          } else if (state is Uninitialized) {
            return SplashScreen();
          }

          return Container();
        },
      ),

Answer 1

您忘记为 BlocBuilder 小部件提供 Bloc 和 State 类型

MaterialApp(
      debugShowCheckedModeBanner: false,
      theme: ThemeData(primarySwatch: Colors.deepPurple),
      /// You need to specify the type here, 
      /// that's why you got error Bloc<dynamic, dynamic>
      home: BlocBuilder<AuthenticationBloc, AuthenticationState>(
        builder: (context, state) {
          print(state);
          if (state is Authenticated) {
            return MainPage();
          } else if (state is Unauthenticated) {
            return LoginPage();
          } else if (state is Uninitialized) {
            return SplashScreen();
          }

          return Container();
        },
      ),

Answer 2

作为错误，本身就提示BlocProvider没有访问权限context使用bloc

MultiBlocProvider 提供了添加多个提供者的能力，这样就可以获得正确的上下文访问，因为 MultiBlocProvider 将 BlocProvider 列表转换为嵌套的树 BlocProvider 个小部件。

MultiBlocProvider(
          providers: [
            BlocProvider<YourBloc>(
                create: (BuildContext context) =>)
          ],
          child: MaterialApp(
            home: BlocBuilder<YourBloc, YourState>(

BlocProvider.of() 使用不包含 Bloc<dynamic,dynamic> 类型的 Bloc 的上下文调用

BlocProvider.of() called with a context that does not contain a Bloc of type Bloc<dynamic,dynamic>

flutter

bloc

flutter-bloc