yii2 i18n学习

举例说明常见的翻译：Yii::t('app','Login')；
追踪源码：BaseYii.php 文件 ，Yii::t($category, $message, $params = [], $language = null) 这个方法实际上是 \yii\i18n\I18N::translate()的一个捷径方法

  /**

      * Translates a message to the specified language.

      *

      * This is a shortcut method of [[\yii\i18n\I18N::translate()]].

      *

      * The translation will be conducted according to the message category and the target language will be used.

      *

      * You can add parameters to a translation message that will be substituted（取代） with the corresponding（相应的） value after

      * translation. The format for this is to use curly brackets around the parameter name as you can see in the following example:

      *

      * ```php

      * $username = 'Alexander';

      * echo \Yii::t('app', 'Hello, {username}!', ['username' => $username]);

      * ```

      *

      * Further formatting of message parameters is supported using the [PHP intl extensions](http://www.php.net/manual/en/intro.intl.php)

      * message formatter. See [[\yii\i18n\I18N::translate()]] for more details.

      *

      * @param string $category the message category.

      * @param string $message the message to be translated.

      * @param array $params the parameters that will be used to replace the corresponding placeholders in the message.

      * @param string $language the language code (e.g. `en-US`, `en`). If this is null, the current

      * [[\yii\base\Application::language|application language]] will be used.

      * @return string the translated message.

      */

     public static function t($category, $message, $params = [], $language = null)

     {

         if (static::$app !== null) {

             return static::$app->getI18n()->translate($category, $message, $params, $language ?: static::$app->language);

         } else {

             $p = [];

             foreach ((array) $params as $name => $value) {

                 $p['{' . $name . '}'] = $value;

             }

             return ($p === []) ? $message : strtr($message, $p);

         }

     }

查看 \yii\i18n\I18N::translate()方法：

 /**

      * Translates a message to the specified language.

      *

      * After translation the message will be formatted using [[MessageFormatter]] if it contains

      * ICU message format and `$params` are not empty.

      *

      * @param string $category the message category.

      * @param string $message the message to be translated.

      * @param array $params the parameters that will be used to replace the corresponding placeholders in the message.

      * @param string $language the language code (e.g. `en-US`, `en`).

      * @return string the translated and formatted message.

      */

     public function translate($category, $message, $params, $language)

     {

         // 返回MessageSource the message source for the given category.

         $messageSource = $this->getMessageSource($category);

         //返回翻译的内容

         $translation = $messageSource->translate($category, $message, $language);

         //格式话翻译的内容

         if ($translation === false) {

             return $this->format($message, $params, $messageSource->sourceLanguage);

         } else {

             return $this->format($translation, $params, $language);

         }

     }

其中 $messageSource = $this->getMessageSource($category);//根据配置文件内容和给的参数$category 返回继承MessageSource 相应子类的实例对象，本例根据配置文件返回PhpMessageSource对象

 <?php

 return [

     'vendorPath' => dirname(dirname(__DIR__)) . '/vendor',

     'components' => [

         'cache' => [

             'class' => 'yii\caching\FileCache',

         ],

         'i18n'=>[

             'translations' => [

                 'app*'=> [

                     'class' => 'yii\i18n\PhpMessageSource',

                     'basePath'=>'@common/messages',

                     'fileMap'=>[

                         'app'=>'app.php',

                     ],

                 ],

             ],

         ],

     ],

 ];

$messageSource = $this->getMessageSource($category); 返回继承MessageSource 相应子类的实例对象

  /**

      * Returns the message source for the given category.

      * @param string $category the category name.

      * @return MessageSource the message source for the given category.

      * @throws InvalidConfigException if there is no message source available for the specified category.

      */

     //根据配置文件内容和 给的参数$category 返回继承MessageSource 相应子类的实例对象， 本例根据配置文件返回PhpMessageSource对象

     public function getMessageSource($category)

     {

         if (isset($this->translations[$category])) {

             $source = $this->translations[$category];

             if ($source instanceof MessageSource) {

                 return $source;

             } else {

                 return $this->translations[$category] = Yii::createObject($source);

             }

         } else {

             // try wildcard matching

             foreach ($this->translations as $pattern => $source) {

                 if (strpos($pattern, '*') > 0 && strpos($category, rtrim($pattern, '*')) === 0) {

                     if ($source instanceof MessageSource) {

                         return $source;

                     } else {

                         return $this->translations[$category] = $this->translations[$pattern] = Yii::createObject($source);

                     }

                 }

             }

             // match '*' in the last

             if (isset($this->translations['*'])) {

                 $source = $this->translations['*'];

                 if ($source instanceof MessageSource) {

                     return $source;

                 } else {

                     return $this->translations[$category] = $this->translations['*'] = Yii::createObject($source);

                 }

             }

         }

         throw new InvalidConfigException("Unable to locate message source for category '$category'.");

     }

再根据实例对象的translate方法返回翻译的内容， $translation = $messageSource->translate($category, $message, $language);

MessageSource 类的 translate方法如下：

   /**

      * Translates a message to the specified language.

      *

      * Note that unless [[forceTranslation]] is true, if the target language

      * is the same as the [[sourceLanguage|source language]], the message

      * will NOT be translated.

      *

      * If a translation is not found, a [[EVENT_MISSING_TRANSLATION|missingTranslation]] event will be triggered.

      *

      * @param string $category the message category

      * @param string $message the message to be translated

      * @param string $language the target language

      * @return string|boolean the translated message or false if translation wasn't found or isn't required

      */

     // 翻译一段信息为指定的语言文件下的内容

     public function translate($category, $message, $language)

     {

         if ($this->forceTranslation || $language !== $this->sourceLanguage) {

             return $this->translateMessage($category, $message, $language);

         } else {

             return false;

         }

     }

$this->translateMessage($category, $message, $language);

  /**

      * Translates the specified message.

      * If the message is not found, a [[EVENT_MISSING_TRANSLATION|missingTranslation]] event will be triggered.

      * If there is an event handler, it may provide a [[MissingTranslationEvent::$translatedMessage|fallback translation]].

      * If no fallback translation is provided this method will return `false`.

      * @param string $category the category that the message belongs to.

      * @param string $message the message to be translated.

      * @param string $language the target language.

      * @return string|boolean the translated message or false if translation wasn't found.

      */

     protected function translateMessage($category, $message, $language)

     {

         $key = $language . '/' . $category;

         if (!isset($this->_messages[$key])) {

             // $language = 'zh-CN'  $category = 'app'

             // $this->loadMessages($category, $language) 为合并后的指定类别语言的翻译数组 key => value

             $this->_messages[$key] = $this->loadMessages($category, $language);

         }

         if (isset($this->_messages[$key][$message]) && $this->_messages[$key][$message] !== '') {

             return $this->_messages[$key][$message];

         } elseif ($this->hasEventHandlers(self::EVENT_MISSING_TRANSLATION)) {

             $event = new MissingTranslationEvent([

                 'category' => $category,

                 'message' => $message,

                 'language' => $language,

             ]);

             $this->trigger(self::EVENT_MISSING_TRANSLATION, $event);

             if ($event->translatedMessage !== null) {

                 return $this->_messages[$key][$message] = $event->translatedMessage;

             }

         }

         return $this->_messages[$key][$message] = false;

     }

根据配置文件生成的 MessageSource子类相应对象的loadMessages方法，生成翻译的文件数组内容，在根据内容查找相应的以$message为键的对应值：
return $this->_messages[$key][$message];

本例根据PhpMessageSource对象的translateMessage方法为例说明：

   /**

      * Loads the message translation for the specified $language and $category.

      * If translation for specific locale code such as `en-US` isn't found it

      * tries more generic `en`. When both are present, the `en-US` messages will be merged

      * over `en`. See [[loadFallbackMessages]] for details.

      * If the $language is less specific than [[sourceLanguage]], the method will try to

      * load the messages for [[sourceLanguage]]. For example: [[sourceLanguage]] is `en-GB`,

      * $language is `en`. The method will load the messages for `en` and merge them over `en-GB`.

      *

      * @param string $category the message category

      * @param string $language the target language

      * @return array the loaded messages. The keys are original messages, and the values are the translated messages.

      * @see loadFallbackMessages

      * @see sourceLanguage

      */

     protected function loadMessages($category, $language)

     {

         //返回指定类别和语言的文件路径

         $messageFile = $this->getMessageFilePath($category, $language);

         // 根据文件路径，加载翻译文件，为数组键值对

         $messages = $this->loadMessagesFromFile($messageFile);

         $fallbackLanguage = substr($language, 0, 2);

         $fallbackSourceLanguage = substr($this->sourceLanguage, 0, 2);

         if ($language !== $fallbackLanguage) {

             // $language = 'zh-CN'    $fallbackLanguage = 'zh'  合并语言zh-CN和zh文件为新的$messages

             $messages = $this->loadFallbackMessages($category, $fallbackLanguage, $messages, $messageFile);

         } elseif ($language === $fallbackSourceLanguage) {

             //  $language = 'zh'    $fallbackLanguage = 'zh' $this->sourceLanguage = 'en' 合并zh 文件和en 文件，当zh文件翻译key的value信息没有时用 en 文件的相应的value 替代，合并为新的翻译数组内容 $messages

             $messages = $this->loadFallbackMessages($category, $this->sourceLanguage, $messages, $messageFile);

         } else {

             if ($messages === null) {

                 Yii::error("The message file for category '$category' does not exist: $messageFile", __METHOD__);

             }

         }

         return (array) $messages;

     }

 //返回指定类别和语言的文件路径

$messageFile = $this->getMessageFilePath($category, $language);

  /**

      * Returns message file path for the specified language and category.

      *

      * @param string $category the message category

      * @param string $language the target language

      * @return string path to message file

      */

     //返回指定的语言和类别文件路径

     protected function getMessageFilePath($category, $language)

     {

         //语言类别文件路径

         $messageFile = Yii::getAlias($this->basePath) . "/$language/";

         if (isset($this->fileMap[$category])) {

             $messageFile .= $this->fileMap[$category];

         } else {

             $messageFile .= str_replace('\\', '/', $category) . '.php';

         }

         return $messageFile;

     }

// 根据文件路径，加载翻译文件，为数组键值对
$messages = $this->loadMessagesFromFile($messageFile);

  /**

      * Loads the message translation for the specified language and category or returns null if file doesn't exist.

      *

      * @param string $messageFile path to message file

      * @return array|null array of messages or null if file not found

      */

     //加载翻译文件，翻译文件为数组文件

     protected function loadMessagesFromFile($messageFile)

     {

         if (is_file($messageFile)) {

             $messages = include($messageFile);

             if (!is_array($messages)) {

                 $messages = [];

             }

             return $messages;

         } else {

             return null;

         }

     }

//根据不同的条件,从其他文件中补充语言文件的缺少的key 的值value 
$messages = $this->loadFallbackMessages($category, $this->sourceLanguage, $messages, $messageFile);

 /**

      * The method is normally called by [[loadMessages]] to load the fallback messages for the language.

      * Method tries to load the $category messages for the $fallbackLanguage and adds them to the $messages array.

      *

      * @param string $category the message category

      * @param string $fallbackLanguage the target fallback language

      * @param array $messages the array of previously loaded translation messages.

      * The keys are original messages, and the values are the translated messages.

      * @param string $originalMessageFile the path to the file with messages. Used to log an error message

      * in case when no translations were found.

      * @return array the loaded messages. The keys are original messages, and the values are the translated messages.

      * @since 2.0.7

      */

     protected function loadFallbackMessages($category, $fallbackLanguage, $messages, $originalMessageFile)

     {

         // 返回的信息文件路径

         $fallbackMessageFile = $this->getMessageFilePath($category, $fallbackLanguage);

         //根据文件路径信息，加载文件的内容

         $fallbackMessages = $this->loadMessagesFromFile($fallbackMessageFile);

         if (

             $messages === null && $fallbackMessages === null

             && $fallbackLanguage !== $this->sourceLanguage

             && $fallbackLanguage !== substr($this->sourceLanguage, 0, 2)

         ) {

             Yii::error("The message file for category '$category' does not exist: $originalMessageFile "

                 . "Fallback file does not exist as well: $fallbackMessageFile", __METHOD__);

         } elseif (empty($messages)) {

             return $fallbackMessages;

         } elseif (!empty($fallbackMessages)) {

             // 当$message数组key 值为空时，且$fallbackMessages对应的key的翻译内容存在是，把$fallbackMessages的内容翻译数组赋值给 $messages[$key]

             foreach ($fallbackMessages as $key => $value) {

                 if (!empty($value) && empty($messages[$key])) {

                     $messages[$key] = $fallbackMessages[$key];

                 }

             }

         }

         return (array) $messages;

     }

最后返回$messages:

return (array) $messages;

根据提供的参数（$message）把$message作为key 查找 $messages 数组中对应的key的值

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yii2 i18n学习

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