Yii源码阅读笔记（二十）

View中应用布局和缓存内容部分：

   /**
      * Begins recording a block.
      * This method is a shortcut to beginning [[Block]]
      * 数据块开始的标记，该方法是开始[Block]的快捷方式
      * 数据块可以在一个地方指定视图内容在另一个地方显示，通常和布局一起使用
      * @param string $id the block ID.
      * @param boolean $renderInPlace whether to render the block content in place.
      * Defaults to false, meaning the captured block will not be displayed.
      * @return Block the Block widget instance
      */
     public function beginBlock($id, $renderInPlace = false)
     {
         return Block::begin([
             'id' => $id,//数据块唯一标识
             'renderInPlace' => $renderInPlace,//是否显示标记，默认false不显示
             'view' => $this,
         ]);
     }

     /**
      * Ends recording a block.
      * 数据块结束的标记
      */
     public function endBlock()
     {
         Block::end();
     }

     /**
      * Begins the rendering of content that is to be decorated by the specified view.
      * 开始用指定的view渲染内容，该方法用来实现嵌套布局，传入的第一个参数为布局文件的路径
      * This method can be used to implement nested layout. For example, a layout can be embedded
      * in another layout file specified as '@app/views/layouts/base.php' like the following:
      *
      * ```php
      * <?php $this->beginContent('@app/views/layouts/base.php'); ?>
      * //...layout content here...
      * <?php $this->endContent(); ?>
      * ```
      *
      * @param string $viewFile the view file that will be used to decorate the content enclosed by this widget.
      * This can be specified as either the view file path or path alias.
      * @param string $viewFile 布局文件
      * @param array $params the variables (name => value) to be extracted and made available in the decorative view.
      * @param array $params 布局view文件的参数
      * @return ContentDecorator the ContentDecorator widget instance
      * @see ContentDecorator
      */
     public function beginContent($viewFile, $params = [])
     {
         return ContentDecorator::begin([
             'viewFile' => $viewFile,
             'params' => $params,
             'view' => $this,
         ]);
     }

     /**
      * Ends the rendering of content.
      * 结束渲染内容
      */
     public function endContent()
     {
         ContentDecorator::end();
     }

     /**
      * Begins fragment caching.
      * 开始片段缓存
      * This method will display cached content if it is available.
      * 该方法将展示可用的缓存内容，否则将开始缓存内容直到出现[endCache()]方法
      * If not, it will start caching and would expect an [[endCache()]]
      * call to end the cache and save the content into cache.
      * A typical usage of fragment caching is as follows,
      * 使用缓存的典型例子如下：
      * ```php
      * if ($this->beginCache($id)) {
      *     // ...generate content here
      *     $this->endCache();
      * }
      * ```
      *
      * @param string $id a unique ID identifying the fragment to be cached.
      * @param array $properties initial property values for [[FragmentCache]]
      * @return boolean whether you should generate the content for caching.
      * False if the cached version is available.
      */
     public function beginCache($id, $properties = [])
     {
         $properties['id'] = $id;//缓存唯一标识
         $properties['view'] = $this;
         /* @var $cache FragmentCache */
         $cache = FragmentCache::begin($properties);
         if ($cache->getCachedContent() !== false) {//如果从缓存中读取到了缓存的内容，则渲染内容并返回 false，因此将跳过内容生成逻辑，不再进行缓存
             $this->endCache();

             return false;
         } else {
             return true;
         }
     }

     /**
      * Ends fragment caching.
      * 结束片段缓存
      */
     public function endCache()
     {
         FragmentCache::end();
     }

     /**
      * Marks the beginning of a page.
      * 页面开始标记--用于生成页面布局文件
      */
     public function beginPage()
     {
         ob_start();
         ob_implicit_flush(false);

         $this->trigger(self::EVENT_BEGIN_PAGE);
     }

     /**
      * Marks the ending of a page.
      * 页面结束标记--用于生成页面布局文件
      */
     public function endPage()
     {
         $this->trigger(self::EVENT_END_PAGE);
         ob_end_flush();
     }