آموزش چند زبانه کردن برنامه های فلاتر

dependencies:
  flutter:
    sdk: flutter
  flutter_localizations:
    sdk: flutter

abstract class Languages {
  
  static Languages of(BuildContext context) {
    return Localizations.of<Languages>(context, Languages);
  }

  String get appName;

  String get labelWelcome;

  String get labelInfo;

  String get labelSelectLanguage;

}

class LanguageEn extends Languages {

  @override
  String get appName => "Multi-languages";

  @override
  String get labelWelcome => "Welcome";

  @override
  String get labelSelectLanguage => "Select Language";

  @override
  String get labelInfo => "This is multi-languages demo application";
  
}

import 'languages.dart';

class LanguageAr extends Languages {

  @override
  String get appName => "متعدد اللغات";

  @override
  String get labelWelcome => "أهلا بك";

  @override
  String get labelSelectLanguage => "اختار اللغة";

  @override
  String get labelInfo => "هذا هو التطبيق التجريبي متعدد اللغات";

}

import 'languages.dart';

class LanguageHi extends Languages {
  
  @override
  String get appName => "बहु भाषा";

  @override
  String get labelWelcome => "स्वागत हे";

  @override
  String get labelSelectLanguage => "भाषा का चयन करें";

  @override
  String get labelInfo => "यह मल्टी लैंग्वेज डेमो एप्लीकेशन है";
  
}

class AppLocalizationsDelegate extends LocalizationsDelegate<Languages> {

  const AppLocalizationsDelegate();

  @override
  bool isSupported(Locale locale) =>
      ['en', 'ar', 'hi'].contains(locale.languageCode);

  @override
  Future<Languages> load(Locale locale) => _load(locale);

  static Future<Languages> _load(Locale locale) async {
    switch (locale.languageCode) {
      case 'en':
        return LanguageEn();
      case 'ar':
        return LanguageAr();
      case 'hi':
        return LanguageHi();
      default:
        return LanguageEn();
    }
  }

  @override
  bool shouldReload(LocalizationsDelegate<Languages> old) => false;
  
}

supportedLocales: [
        Locale('en', ''),
        Locale('ar', ''),
        Locale('hi', '')
      ]

void main() {
  runApp(MyApp());
}

class MyApp extends StatefulWidget {

  static void setLocale(BuildContext context, Locale newLocale) {
    var state = context.findAncestorStateOfType<_MyAppState>();
    state.setLocale(newLocale);
  }

  @override
  State<StatefulWidget> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {


  Locale _locale;

  void setLocale(Locale locale) {
    setState(() {
      _locale = locale;
    });
  }

  @override
  void didChangeDependencies() async {
    getLocale().then((locale) {
      setState(() {
        _locale = locale;
      });
    });
    super.didChangeDependencies();
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      builder: (context, child) {
        return MediaQuery(
          child: child,
          data: MediaQuery.of(context).copyWith(textScaleFactor: 1.0),
        );
      },
      title: 'Multi Language',
      debugShowCheckedModeBanner: false,
      locale: _locale,
      home: Home(),
      supportedLocales: [
        Locale('en', ''),
        Locale('ar', ''),
        Locale('hi', '')
      ],
      localizationsDelegates: [
        AppLocalizationsDelegate(),
        GlobalMaterialLocalizations.delegate,
        GlobalWidgetsLocalizations.delegate,
        GlobalCupertinoLocalizations.delegate,
      ],
      localeResolutionCallback: (locale, supportedLocales) {
        for (var supportedLocale in supportedLocales) {
          if (supportedLocale?.languageCode == locale?.languageCode &&
              supportedLocale?.countryCode == locale?.countryCode) {
            return supportedLocale;
          }
        }
        return supportedLocales?.first;
      },
    );
  }
}

const String prefSelectedLanguageCode = "SelectedLanguageCode";

Future<Locale> setLocale(String languageCode) async {
  SharedPreferences _prefs = await SharedPreferences.getInstance();
  await _prefs.setString(prefSelectedLanguageCode, languageCode);
  return _locale(languageCode);
}

Future<Locale> getLocale() async {
  SharedPreferences _prefs = await SharedPreferences.getInstance();
  String languageCode = _prefs.getString(prefSelectedLanguageCode) ?? "en";
  return _locale(languageCode);
}

Locale _locale(String languageCode) {
  return languageCode != null && languageCode.isNotEmpty
      ? Locale(languageCode, '')
      : Locale('en', '');
}

void changeLanguage(BuildContext context, String selectedLanguageCode) async {
  var _locale = await setLocale(selectedLanguageCode);
  MyApp.setLocale(context, _locale);
}