flutter bloc：变量未在 BlocBuilder 中定义

Question

I am trying to use Flutter bloc in my project.After creating State and Event class in State i have a LanguageLoad class:

abstract class LanguageState extends Equatable {
  const LanguageState();
  @override
  List<Object> get props => [];
}

class LanguageInitial extends LanguageState {}

class LanguageLoad extends LanguageState {
  final Locale locale;
  LanguageLoad(this.locale);
  @override
  List<Object> get props => [locale];
}

After creating bloc class i am using in main class:

    void main() {
      WidgetsFlutterBinding.ensureInitialized();
      runApp(
        BlocProvider(
            create: (_) => LanguageBloc()..add(LanguageLoadStarted()),
            child: MyApp()),
      );
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return BlocBuilder<LanguageBloc, LanguageState>(
      builder: (context, languageState) => MaterialApp(
        debugShowCheckedModeBanner: false,
        locale: languageState.locale, // locale is not defined
}

But I don't know why locale is not defined in locale: languageState.locale ?

Answer 1

You don't know the type of languageState and you need to cast it to obtain locale value. This is a piece of my in production app:

BlocBuilder<LanguageBloc, LanguageState>(
    builder: (context, state) {
      Locale locale;
      if (state is LanguageLoaded) {
        locale = state.locale;
      }
      return MaterialApp(
        locale: locale,

In my case I load MaterialApp even if Locale first time is null. It depends by you app logic.