Flutter ios 国际化(复制粘贴 中英文切换等问题)

前提

在做flutter ios 国际化的时候遇到长按文本框崩溃的问题,然后google到一堆写法是重写cupertinoLocalization的奇怪做法,然后还千篇一律都是这么改的,其实不用那么麻烦,一个代码就可以解决的问题

Flutter 中文网的例子

因为FLutter默认值支持美国英语的本地化,所以需要用到flutter_localizations的库,目前,软件包支持15中语言。

引入:flutter_localizations

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

使用:

import 'package:flutter_localizations/flutter_localizations.dart';

new MaterialApp(
 localizationsDelegates: [
   // ... app-specific localization delegate[s] here
   GlobalMaterialLocalizations.delegate,
   GlobalWidgetsLocalizations.delegate,
 ],
 supportedLocales: [
    const Locale('en', 'US'), // English
    const Locale('he', 'IL'), // Hebrew
    // ... other locales the app supports
  ],
  // ...
)

问题1:

按照Flutter中文网提供的这个例子来使用,在android中已经可以进行语言切换,实现对应的中英文切换了,但是在iphone中通过长按输入框,就会出错(get方法为空),提示为:

The getter 'pasteButtonLabel' was called on null.
Receiver: null
Tried calling: pasteButtonLabel

方案1:

这个错误,在天星银行里面也有,修复之后不会出现中文文案的提示。具体的修复代码如下:

class CupertinoLocalizationsDelegate extends LocalizationsDelegate {
  const CupertinoLocalizationsDelegate();

  @override
  bool isSupported(Locale locale) => true;

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

  @override
  bool shouldReload(CupertinoLocalizationsDelegate old) => false;

  @override
  String toString() => 'DefaultCupertinoLocalizations.delegate(zh_CH)';
}

--------------------------------------

localizationsDelegates: [
   // ... app-specific localization delegate[s] here
   GlobalMaterialLocalizations.delegate,
   GlobalWidgetsLocalizations.delegate,
   CupertinoLocalizationsDelegate(),
 ],


添加如上代码之后,长按ios 会出现英文的cut、paste等文案,但是不会随着语言的切换本地化语言

原因是重写了LocalizationsDelegate,在isSupported返回true,不管当前是什么语言,我统统给你返回英文的默认文案(DefaultCupertinoLocalizations),改法显然是错误的。

方案2:

 @override
  Future load(Locale locale) {
    if (locale.languageCode == 'zh') {
      print('locale.languageCode');
      return ChineseCupertinoLocalizations.load(locale);
    }
    return DefaultCupertinoLocalizations.load(locale);
  }

ChineseCupertinoLocalizations是 新写的类 继承 CupertinoLocalizations 实现所有的method

class ChineseCupertinoLocalizations implements CupertinoLocalizations {
    
    .....
    
  @override
  String get cutButtonLabel => '剪切';

  @override
  String get copyButtonLabel => '复制';

  @override
  String get pasteButtonLabel => '粘贴';

  @override
  String get selectAllButtonLabel => '全选';
  
  .....
}

经过上述操作,问题是解决了,但是感觉不太对:

1、flutter_localizations 本身支持十几种语言,android 切换没有问题,ios 却有问题。

2、如果国际化更多的语言,难道要每个语言实现一遍CupertinoLocalizations,思路明显有问题。

分析

MaterialApp 提供的参数localizationsDelegates列表中的元素是生本地集合的工厂,其中GlobalMaterialLocalizations.delegate为Material Components库提供了本地化的字符串和其他值。GlobalWidgetsLocalizations.delegate定义widget默认的文本方向,从左到右或从右到左(如沙特语言)。

LocalizationsDelegate是何物?我们看一下源码

abstract class LocalizationsDelegate {

  bool isSupported(Locale locale);
  
  Future load(Locale locale);
  
  bool shouldReload(covariant LocalizationsDelegate old);
  Type get type => T;

  @override
  String toString() => '${objectRuntimeType(this, 'LocalizationsDelegate')}[$type]';
}

LocalizationsDelegate 提供了 三个关键函数:分别是isSupportedloadshouldReload

flutter为了减小包的大小,仅仅提供了英文的MaterialLocalizationsCupertinoLocalizations的实现,分别是DefaultMaterialLocalizationsDefaultCupertinoLocalizations所以在语言是英文的情况下,即使不引入flutter_localizations库 一些系统的文本是没有问题的,但是本地语言是英文之外的语言,就需要这个库了。

按照官方的写法引入:

localizationsDelegates: [
        // 本地化代理
        GlobalMaterialLocalizations.delegate,
        GlobalWidgetsLocalizations.delegate,
      ],

Material Components库是支持iOS、android、web 三段通用的风格,所以正常提供GlobalMaterialLocalizations.delegate提供的本地化字符串和其他值,应该是三段通用的。但是从现象上看是有问题的(下面解释),查看GlobalMaterialLocalizations.delegate的实现中有一个函数:

 static const List> delegates = >[
    GlobalCupertinoLocalizations.delegate,
    GlobalMaterialLocalizations.delegate,
    GlobalWidgetsLocalizations.delegate,
  ];

delegates直接提供了GlobalCupertinoLocalizationsGlobalMaterialLocalizations ,说明flutter_localizations也是支持iOS的国际化设置的。

修改MaterialApp中的参数设置:

      localizationsDelegates: [
        // 本地化代理
        GlobalMaterialLocalizations.delegate,
        GlobalWidgetsLocalizations.delegate,
        GlobalCupertinoLocalizations.delegate,
      ],
      supportedLocales: [
        const Locale('en', ''), // 美国英语
        const Locale('zh', 'HK'), // 中文
        const Locale('ja', ''), // 日语
      ],
       locale: const Locale('en', ''),

在加入GlobalCupertinoLocalizations之后就可以的支持iOS的国际化操作了。

继续查看GlobalMaterialLocalizations中,查看继承自LocalizationsDelegate_MaterialLocalizationsDelegate

isSupported中看到支持的语言:

final Set kMaterialSupportedLanguages = HashSet.from(const [
  'af', // Afrikaans
  'am', // Amharic
  'ar', // Arabic
  'as', // Assamese
  'az', // Azerbaijani
  'be', // Belarusian
  'bg', // Bulgarian
  'bn', // Bengali Bangla
  'bs', // Bosnian
  ......//后面还有好多
]);

load的的返回中:

return SynchronousFuture(getMaterialTranslation(
        locale,
        fullYearFormat,
        compactDateFormat,
        shortDateFormat,
        mediumDateFormat,
        longDateFormat,
        yearMonthFormat,
        shortMonthDayFormat,
        decimalFormat,
        twoDigitZeroPaddedFormat,
      ));

根据getMaterialTranslation 返回对应语言场景下的继承自GlobalMaterialLocalizations的具体实例。

GlobalMaterialLocalizations getMaterialTranslation(
  Locale locale,
  intl.DateFormat fullYearFormat,
  intl.DateFormat compactDateFormat,
  intl.DateFormat shortDateFormat,
  intl.DateFormat mediumDateFormat,
  intl.DateFormat longDateFormat,
  intl.DateFormat yearMonthFormat,
  intl.DateFormat shortMonthDayFormat,
  intl.NumberFormat decimalFormat,
  intl.NumberFormat twoDigitZeroPaddedFormat,
) {
  switch (locale.languageCode) {
    case 'af':
      return MaterialLocalizationAf(fullYearFormat: fullYearFormat, compactDateFormat: compactDateFormat, shortDateFormat: shortDateFormat, mediumDateFormat: mediumDateFormat, longDateFormat: longDateFormat, yearMonthFormat: yearMonthFormat, shortMonthDayFormat: shortMonthDayFormat, decimalFormat: decimalFormat, twoDigitZeroPaddedFormat: twoDigitZeroPaddedFormat);
    case 'am':
      return MaterialLocalizationAm(fullYearFormat: fullYearFormat, compactDateFormat: compactDateFormat, shortDateFormat: shortDateFormat, mediumDateFormat: mediumDateFormat, longDateFormat: longDateFormat, yearMonthFormat: yearMonthFormat, shortMonthDayFormat: shortMonthDayFormat, decimalFormat: decimalFormat, twoDigitZeroPaddedFormat: twoDigitZeroPaddedFormat);
    case 'ar':
      return MaterialLocalizationAr(fullYearFormat: fullYearFormat, compactDateFormat: compactDateFormat, shortDateFormat: shortDateFormat, mediumDateFormat: mediumDateFormat, longDateFormat: longDateFormat, yearMonthFormat: yearMonthFormat, shortMonthDayFormat: shortMonthDayFormat, decimalFormat: decimalFormat, twoDigitZeroPaddedFormat: twoDigitZeroPaddedFormat);
      ......//很多语言
    

App通过启动,或者切换语言的时候,替换MaterialApp中的'locale'对象来切换语言,同时,切换的语言对象要在supportedLocales中,否则默认返回supportedLocales中的第一个语言,如果一个都没有,默认返回英文

supportedLocales: [
        const Locale('ja', ''), // 日语
        const Locale('en', ''), // 美国英语
        const Locale('zh', 'HK'), // 中文

        //其它Locales
      ],
 locale: const Locale('zh', ''),

问题:

既然GlobalMaterialLocalizations是iOS和android 通用的风格,在Flutter中文网 介绍的接入国际化的时候也只提到了GlobalMaterialLocalizations感觉这明显是有问题的。

DefalutCupertinoLocalization中我们检索cutButtonLabel属性,我们看一下那些地方在使用:

内容:

  @override
  String get cutButtonLabel => 'Cut';

  @override
  String get copyButtonLabel => 'Copy';

  @override
  String get pasteButtonLabel => 'Paste';

结果发现有两处地方在使用:

flutter > lib > src > material > text_selection.dart
flutter > lib > scr > cupertino > text_selection.dart

在这两个textSelection的build函数中,获取的Localizations分别是materialcupertino的:

@override
  Widget build(BuildContext context) {
    // Don't render the menu until the state of the clipboard is known.
    if (widget.handlePaste != null
        && _clipboardStatus.value == ClipboardStatus.unknown) {
      return const SizedBox(width: 0.0, height: 0.0);
    }
    print('text_selected---------------------------CupertinoLocalizations');
    final List items = [];
    final CupertinoLocalizations localizations = CupertinoLocalizations.of(context);
    final EdgeInsets arrowPadding = widget.isArrowPointingDown
      ? EdgeInsets.only(bottom: _kToolbarArrowSize.height)
      : EdgeInsets.only(top: _kToolbarArrowSize.height);
    final Widget onePhysicalPixelVerticalDivider =
        SizedBox(width: 1.0 / MediaQuery.of(context).devicePixelRatio);

@override
  Widget build(BuildContext context) {
    // Don't render the menu until the state of the clipboard is known.
    if (widget.handlePaste != null
        && _clipboardStatus.value == ClipboardStatus.unknown) {
      return const SizedBox(width: 0.0, height: 0.0);
    }
    print('text_selected---------------------------MaterialLocalizations');
    final MaterialLocalizations localizations = MaterialLocalizations.of(context);
    final List<_ItemData> itemDatas = <_ItemData>[
      if (widget.handleCut != null)
        _ItemData(widget.handleCut, localizations.cutButtonLabel),
      if (widget.handleCopy != null)
        _ItemData(widget.handleCopy, localizations.copyButtonLabel),
      if (widget.handlePaste != null
          && _clipboardStatus.value == ClipboardStatus.pasteable)
        _ItemData(widget.handlePaste, localizations.pasteButtonLabel),
      if (widget.handleSelectAll != null)
        _ItemData(widget.handleSelectAll, localizations.selectAllButtonLabel),
    ];

加上print之后发现,在iOS设备上加载的cupertinotext_selected,android上是materialtext_selected ,

由此真相大白。

正常实现系统文本的国际化只需要在MaterialApp的初始化中加入:

  localizationsDelegates: [
        // 本地化代理
        GlobalMaterialLocalizations.delegate,
        GlobalWidgetsLocalizations.delegate,
        GlobalCupertinoLocalizations.delegate,
      ],

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