Flutter ARB 本地化抛出 "the getter was called on null" 错误

Question

按照 official internationalization tutorial 的提示，我在尝试使用从 ARB 文件自动生成的翻译引擎 (AppLocalizations.of(context).helloWrold) 时得到 The getter was called on null:

import 'package:flutter/material.dart';
import 'package:flutter_gen/gen_l10n/app_localizations.dart';

class Login extends StatelessWidget {
  final loginAction;
  final String loginError;

  const Login(this.loginAction, this.loginError);

  @override
  Widget build(BuildContext context) {
    return Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        RaisedButton(
          onPressed: () {
            loginAction();
          },
          child: Text(AppLocalizations.of(context).helloWorld),
        ),
        Text(loginError ?? ''),
      ],
    );
  }
}

Answer 1

这个问题的解决方法是官方教程遗漏的部分。那里没有描述要让引擎运行，需要在 main.dart 文件中声明额外的委托。这样就可以得出结论了example GitHub repository。要解决此问题，请转到 MaterialApp 并添加缺少的委托 AppLocalizations.delegate:

import 'package:flutter_gen/gen_l10n/app_localizations.dart';
import 'package:flutter_localizations/flutter_localizations.dart';


      child: MaterialApp(
          localizationsDelegates: [
            // ... app-specific localization delegate[s] here
            AppLocalizations.delegate,
            GlobalMaterialLocalizations.delegate,
            GlobalWidgetsLocalizations.delegate,
            GlobalCupertinoLocalizations.delegate,
          ],
          supportedLocales: [
            const Locale('en', ''),
            const Locale('pl', '')
          ],
          home: Scaffold(

Flutter ARB 本地化抛出 "the getter was called on null" 错误

Flutter ARB localization throws "the getter was called on null" error

localization

dart

flutter