Flutter的国际化:轻松实现多语言支持

算法架构师 2019-02-25 ⋅ 12 阅读

在移动应用开发中,为用户提供多语言支持是非常重要的。Flutter作为一个强大的跨平台开发框架,为开发者提供了很多便利的功能,包括国际化支持。在本文中,我们将探讨如何使用Flutter的国际化功能来轻松实现多语言支持。

1. 添加依赖

首先,在Flutter项目的pubspec.yaml文件中添加flutter_localizations依赖:

dependencies:
  flutter_localizations:
    sdk: flutter

然后通过运行flutter packages get命令来获取依赖。

2. 创建语言包

在项目的lib目录下创建一个l10n目录,用于存放语言相关的文件。在l10n目录中创建一个intl_messages.arb文件,用于存放多语言的消息。

示例intl_messages.arb文件内容:

{
  "@@locale": "en",
  "title": "Flutter Internationalization",
  "welcome": "Welcome to Flutter Internationalization",
  "change_language": "Change Language"
}

可以根据需要在该文件中添加更多的消息和对应的翻译。

3. 生成本地化代码

在项目根目录下打开终端,并执行以下命令:

flutter packages pub run intl_translation:generate_from_arb --output-dir=lib/l10n
  --no-use-deferred-loading lib/l10n/intl_messages.arb

该命令将生成一个messages.dart文件,用于在Flutter应用中访问多语言消息。

4. 设置应用支持的语言

在项目的lib目录下创建一个l10n目录,并在该目录中创建一个generated/目录。然后创建一个名为intl.dart的文件,用于设置应用支持的语言。

示例intl.dart文件内容:

import 'package:flutter/cupertino.dart';
import 'package:flutter/foundation.dart';
import 'package:flutter_localizations/flutter_localizations.dart';

import 'messages_all.dart';

class AppLocalizations {
  static Future<AppLocalizations> load(Locale locale) {
    final String name = locale.countryCode.isEmpty ? locale.languageCode : locale.toString();
    final String localeName = Intl.canonicalizedLocale(name);

    return initializeMessages(localeName).then((_) {
      Intl.defaultLocale = localeName;
      return AppLocalizations();
    });
  }

  static AppLocalizations of(BuildContext context) {
    return Localizations.of<AppLocalizations>(context, AppLocalizations);
  }

  String get title => Intl.message('Flutter Internationalization', name: 'title');
  String get welcome => Intl.message('Welcome to Flutter Internationalization', name: 'welcome');
  String get changeLanguage => Intl.message('Change Language', name: 'change_language');
}

class AppLocalizationsDelegate extends LocalizationsDelegate<AppLocalizations> {
  const AppLocalizationsDelegate();

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

  @override
  Future<AppLocalizations> load(Locale locale) => AppLocalizations.load(locale);

  @override
  bool shouldReload(AppLocalizationsDelegate old) => false;
}

以上代码中,isSupported方法用于指定应用支持的语言,load方法用于加载具体的语言资源,shouldReload方法用于判断是否需要重新加载语言资源。

5. 构建语言资源和本地化Widget

在根Widget中,通过MaterialApplocalizationsDelegatessupportedLocales属性来配置应用的本地化设置。

示例代码:

import 'package:flutter/material.dart';
import 'package:flutter_localizations/flutter_localizations.dart';

import 'l10n/generated/intl.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      localizationsDelegates: [
        AppLocalizationsDelegate(),
        GlobalMaterialLocalizations.delegate,
        GlobalWidgetsLocalizations.delegate,
      ],
      supportedLocales: [
        const Locale('en', ''),
        const Locale('zh', ''),
      ],
      title: 'Flutter Internationalization',
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final localizations = AppLocalizations.of(context);

    return Scaffold(
      appBar: AppBar(
        title: Text(localizations.title),
      ),
      body: Center(
        child: Text(
          localizations.welcome,
          style: TextStyle(fontSize: 24.0),
        ),
      ),
    );
  }
}

通过以上配置,应用会根据设备的语言设置来显示对应的多语言消息。

6. 切换语言

实现切换语言的功能可以通过下面的代码实现:

final List<Locale> supportedLocales = [
  const Locale('en', ''),
  const Locale('zh', ''),
];

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

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  Locale _locale;

  @override
  void initState() {
    super.initState();
    _locale = supportedLocales.first;
  }

  Future<void> _changeLanguage(Locale locale) async {
    setState(() {
      _locale = locale;
    });
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      ...
      supportedLocales: supportedLocales,
      locale: _locale,
      ...
      home: MyHomePage(changeLanguage: _changeLanguage),
    );
  }
}

class MyHomePage extends StatelessWidget {
  final Function(Locale) changeLanguage;

  MyHomePage({this.changeLanguage});

  @override
  Widget build(BuildContext context) {
    final localizations = AppLocalizations.of(context);

    return Scaffold(
      ...
      appBar: AppBar(
        ...
        actions: <Widget>[
          PopupMenuButton<Locale>(
            onSelected: (locale) => changeLanguage(locale),
            itemBuilder: (BuildContext context) {
              return supportedLocales.map((Locale locale) {
                return PopupMenuItem<Locale>(
                  value: locale,
                  child: Text(locale.languageCode),
                );
              }).toList();
            },
          ),
        ],
      ),
      ...
    );
  }
}

通过上述代码,我们可以在应用的AppBar上添加一个PopupMenuButton来实现切换语言的功能。

总结:

Flutter提供了强大的国际化支持,可以帮助我们轻松实现多语言应用程序。通过上述步骤,我们可以配置应用支持的语言、生成本地化代码和构建多语言资源,然后在应用中快速加载并使用这些资源。此外,我们还可以通过切换语言来实现应用的多语言切换功能。希望这篇博客对你理解Flutter的国际化功能有所帮助!


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