Flutter 应用程序使用 i18n Jetbrains 插件的样板构建多语言 AppBar 时崩溃

Question

我按照官方文档使用 Android Studio 的 Flutter i18n 插件。

我向显示字符串的最小应用程序添加了所需的几个配置行：

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      localizationsDelegates: [S.delegate],
      supportedLocales: S.delegate.supportedLocales,
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
//      appBar: AppBar(
//        title: Text("Hard-coded English string"),
//      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(S.of(context).string_that_should_be_internationalized),
          ],
        ),
      ),
    );
  }
}

这是有效的（该字符串实际上被翻译成我的手机系统语言）。但每次调用构建时都会引发警告：

Warning: This application's locale, it_, is not supported by all of its
localization delegates.
> A MaterialLocalizations delegate that supports the it_ locale was not found.

尽管所有 arb 文件都已正确配置S.delegate.supportedLocales。[en_, it_]

我可以使Scaffold主体任意复杂，而行为保持不变（i18n 带有警告）。但是如果我添加一个简单的AppBar（即使widged不需要翻译）到Scaffold整个应用程序崩溃。（例如在上面的代码片段中取消注释）

错误摘要：

I/flutter (11411): No MaterialLocalizations found.
I/flutter (11411): AppBar widgets require MaterialLocalizations to be provided by a Localizations widget ancestor.
I/flutter (11411): Localizations are used to generate many different messages, labels,and abbreviations which are used
I/flutter (11411): by the material library.
I/flutter (11411): To introduce a MaterialLocalizations, either use a  MaterialApp at the root of your application to
I/flutter (11411): include them automatically, or add a Localization widget with a MaterialLocalizations delegate.
I/flutter (11411): The specific widget that could not find a MaterialLocalizations ancestor was:
I/flutter (11411):   AppBar

该框架抱怨我AppBar没有本地化小部件祖先。但它实际上有，因为它位于MaterialApp. 不知道如何解开这个谜团。

完整日志

编辑
我刚刚发现的另一个奇怪的事情：在模式下运行相同的应用程序--release可以消除所有错误和警告；一切都被正确翻译，包括AppBar.
仍然想知道为什么它在模式下崩溃--debug。

Answer 1

问题不在于样板代码或配置。

该错误的含义是“默认系统字符串”不支持语言“it_”。（特别是它会由于 AppBar 的某些默认工具提示而崩溃 -> 这就是如果AppBar显示 则它会崩溃的原因）。

正如本问答中所报告的，您可以通过实施自己的解决方案来解决该问题LocalizationsDelegate.

完全修复

class MaterialLocalizationItDelegate extends LocalizationsDelegate<MaterialLocalizations> {
  /// Here list supported country and language codes
  @override
  bool isSupported(Locale locale) => locale.languageCode == "it";
  /// Here create an instance of your [MaterialLocalizations] subclass
  @override
  Future<MaterialLocalizations> load(Locale locale) async => MaterialLocalizationIt();
  @override
  bool shouldReload(_) => false;
}

class MaterialLocalizationIt extends MaterialLocalizations {
  // alt-enter on intellij and implement many overrides (somthing like 57)
}

然后将您的委托添加到委托列表中：

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      localizationsDelegates: [S.delegate, MaterialLocalizationItDelegate()],  // <- append here
      supportedLocales: S.delegate.supportedLocales,
      home: MyHomePage(),
    );
  }
}

快速解决

在实施 57 个覆盖之前，检查这是否适合您的仓促方法。
准确复制这段代码：

class FallbackLocalizationDelegate extends LocalizationsDelegate<MaterialLocalizations> {
  @override
  bool isSupported(Locale locale) => true;
  @override
  Future<MaterialLocalizations> load(Locale locale) async => DefaultMaterialLocalizations();
  @override
  bool shouldReload(_) => false;
}

上面的类声称支持所有语言环境 ( isSupported(Locale locale) => true) 并仅返回默认的 en_US 语言环境。
最后将其添加到您的代表列表中。

localizationsDelegates: [S.delegate, FallbackLocalizationDelegate()],  // <- append here

此快速修复会将所有默认系统字符串设置为英语，但您的“自定义”本地化应该可以工作。