我目前正在测试驾驶，并且已经按照教程构建了本地化的“
Hello world” 。但是，当我尝试将窗口小部件移至其他文件时，出现红屏死机并显示以下错误：

The following NoSuchMethodError was thrown building ToDoItem(dirty):
The method 'helloWorld' was called on null.
Receiver: null
Tried calling: helloWorld()

我的待办事项类看起来像这样

todo_item.dart

import 'package:flutter/material.dart';
import 'package:to_do_app/localization.dart';

class ToDoItem extends StatelessWidget {

  @override
  Widget build(BuildContext context) {
    return new Text(ToDoLocalizations.of(context).helloWorld());
  }
}

当然，问题在于我的Localization类尚未初始化，但是由于Text窗口小部件没有LocalizationDelegates参数，我不知道如何初始化它。

我知道可以通过将String直接注入到我的小部件的构造函数中来解决此问题，但是出于这个原因，我想知道如何本地化小部件。

编辑： 这是我的本地化课程

import 'dart:async';
import 'dart:developer';
import 'package:flutter/widgets.dart';
import 'package:intl/intl.dart';
import 'package:to_do_app/l10n/messages_all.dart';

class ToDoLocalizations {
  ToDoLocalizations(Locale locale) : _localeName = locale.toString();

  final String _localeName;

  static Future<ToDoLocalizations> load(Locale locale) {
    return initializeMessages(locale.toString()).then((Object _) {
      return new ToDoLocalizations(locale);
    });
  }

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

  String helloWorld() {
    return Intl.message(
        'Hello, World!',
        name: 'helloWorld',
        desc: 'A friendly salutation',
        locale: _localeName
    );
  }
}

class ToDoLocalizationsDelegate
    extends LocalizationsDelegate<ToDoLocalizations> {


  @override
  bool isSupported(Locale locale) {
    return ['en', 'nb'].contains(locale.languageCode);
  }

  @override
  bool shouldReload(LocalizationsDelegate<ToDoLocalizations> old) {
    return false;
  }

  @override
  Future<ToDoLocalizations> load(Locale locale) {
    return ToDoLocalizations.load(locale);
  }
}