black_screen_inv

A flutter test app to investigate a black screen problem on Stack overflow

How to reproduce

To reproduce the problem situatioon, use flutter run to run this app then modity below initialization code in /lib/app.dart

return MaterialApp(
  localizationsDelegates: [
    S.delegate,                       // <--- will cause black screen
    //AppLocalizations.delegate,      // <--- no black screen
    GlobalMaterialLocalizations.delegate,
    GlobalCupertinoLocalizations.delegate,
    GlobalWidgetsLocalizations.delegate,
  ],
  
  ...

Observation

flutter_intl (It will cause black screen)

Apply the flutter_intl to enable the app internationalize. It generates class S with asynchronous future call inside will cause an instantaneous black screen at program start.

static Future<S> load(Locale locale) {
  final name = (locale.countryCode?.isEmpty ?? false)
      ? locale.languageCode
      : locale.toString();
  final localeName = Intl.canonicalizedLocale(name);
  
  return initializeMessages(localeName).then((_) {
    Intl.defaultLocale = localeName;
    final instance = S();
    S._current = instance;

    return instance;
  });
}

intl (It's fine, no black screen)

Follow the internationalize guidance on official flutter.dev generate very similar class _AppLocalizationsDelegate, which is also override the load method as below.

Future<AppLocalizations> load(Locale locale) {
  return SynchronousFuture<AppLocalizations>(_lookupAppLocalizations(locale));
}