class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
        primarySwatch: Colors.red,
      ),
      localizationsDelegates: [
        S.delegate,
        GlobalMaterialLocalizations.delegate,
        GlobalWidgetsLocalizations.delegate,
      ],
      supportedLocales: <Locale>[
        Locale("en", ""),
        Locale("zh", ""),
        Locale("fr", ""),
        Locale("de", ""),
      ],
      localeResolutionCallback: (Locale locale, Iterable<Locale> supported) {

        bool isSupported(Locale locale) {
          if (locale == null) return false;
          if (supported.contains(locale)) {
            return true;
          } else {
            for (Locale supportedLocale in supported) {
              if (supportedLocale.countryCode == null || supportedLocale.countryCode.isEmpty)
                if (supportedLocale.languageCode == locale.languageCode) return true;
            }
            return false;
          }
        }

        if (!isSupported(locale))
          return supported.first;

        final Locale languageLocale = Locale(locale.languageCode, "");
        if (supported.contains(locale)) return locale;
        else if (supported.contains(languageLocale)) return languageLocale;
        else return supported.first;
      },
      home: MyHomePage(),
    );
  }
}