yii2源码学习笔记(十九）

view剩余代码

     /**
      * @return string|boolean the view file currently being rendered. False if no view file is being rendered.
      * 当前正在渲染的视图文件
      */
     public function getViewFile()
     {
         return end($this->_viewFiles);
     }

     /**
      * This method is invoked right before [[renderFile()]] renders a view file.
      * The default implementation will trigger the [[EVENT_BEFORE_RENDER]] event.
      * 前置事件，执行[renderFile()]时被调用，默认触发[[EVENT_BEFORE_RENDER]]事件
      * If you override this method, make sure you call the parent implementation first.
      * @param string $viewFile the view file to be rendered. 要渲染的视图文件。
      * @param array $params the parameter array passed to the [[render()]] method.
      * 参数数组传递到[render()]方法。
      * @return boolean whether to continue rendering the view file. 是否继续渲染视图文件。
      */
     public function beforeRender($viewFile, $params)
     {
         $event = new ViewEvent([//实例化ViewEvent
             'viewFile' => $viewFile,
             'params' => $params,
         ]);
         $this->trigger(self::EVENT_BEFORE_RENDER, $event);//触发[EVENT_BEFORE_RENDER]事件

         return $event->isValid;//判断是否继续渲染文件
     }

     /**
      * This method is invoked right after [[renderFile()]] renders a view file.
      * The default implementation will trigger the [[EVENT_AFTER_RENDER]] event.
      * 后置事件，在执行[renderFile()]方法后被调用，默认触发[[EVENT_AFTER_RENDER]]事件
      * If you override this method, make sure you call the parent implementation first.
      * @param string $viewFile the view file being rendered.要渲染的视图文件。
      * @param array $params the parameter array passed to the [[render()]] method.
      * 参数数组传递到[render()]方法。
      * @param string $output the rendering result of the view file. Updates to this parameter
      * will be passed back and returned by [[renderFile()]].
      * 返回视图渲染的结果
      */
     public function afterRender($viewFile, $params, &$output)
     {
         if ($this->hasEventHandlers(self::EVENT_AFTER_RENDER)) {//判断[EVENT_AFTER_RENDER]事件是否存在
             $event = new ViewEvent([
                 'viewFile' => $viewFile,
                 'params' => $params,
                 'output' => $output,
             ]);
             //触发[EVENT_AFTER_RENDER]事件
             $this->trigger(self::EVENT_AFTER_RENDER, $event);
             $output = $event->output;//返回结果
         }
     }

     /**
      * Renders a view file as a PHP script.
      * 返回一个视图文件当作PHP脚本
      * This method treats the view file as a PHP script and includes the file.
      * It extracts the given parameters and makes them available in the view file.
      * The method captures the output of the included view file and returns it as a string.
      * 将传入的参数转换为变量，包含并执行view文件，返回执行结果
      * This method should mainly be called by view renderer or [[renderFile()]].
      *
      * @param string $_file_ the view file. 视图文件
      * @param array $_params_ the parameters (name-value pairs) that will be extracted and made available in the view file.
      * @return string the rendering result 执行结果
      */
     public function renderPhpFile($_file_, $_params_ = [])
     {
         ob_start(); //打开输出缓冲
         ob_implicit_flush(false); //关闭缓冲区
         extract($_params_, EXTR_OVERWRITE);// 将一个数组转换为变量使用
         require($_file_);

         return ob_get_clean();//得到缓冲区的内容并清除当前输出缓冲
     }

     /**
      * Renders dynamic content returned by the given PHP statements. 渲染动态内容
      * This method is mainly used together with content caching (fragment caching and page caching)
      * 用来聚合缓存的内容
      * when some portions of the content (called *dynamic content*) should not be cached.
      * The dynamic content must be returned by some PHP statements.
      * 渲染某些被PHP语句返回的动态内容
      * @param string $statements the PHP statements for generating the dynamic content.生成动态内容的PHP语句。
      * @return string the placeholder of the dynamic content, or the dynamic content if there is no
      * active content cache currently. 动态内容占位符 如果当前没有有效的内容缓存，调用evaluateDynamicContent输出
      */
     public function renderDynamic($statements)
     {
         if (!empty($this->cacheStack)) {//动态内容的列表不为空
             $n = count($this->dynamicPlaceholders);//统计动态内容条数
             $placeholder = "<![CDATA[YII-DYNAMIC-$n]]>";//生成占位符
             $this->addDynamicPlaceholder($placeholder, $statements);//添加动态内容占位符

             return $placeholder;
         } else {//没有有效缓存 执行传入的PHP语句，返回执行结果
             return $this->evaluateDynamicContent($statements);
         }
     }

     /**
      * Adds a placeholder for dynamic content. 添加一个动态内容占位符
      * This method is internally used. 内部使用
      * @param string $placeholder the placeholder name 占位符名称
      * @param string $statements the PHP statements for generating the dynamic content
      * 生成动态内容的PHP语句
      */
     public function addDynamicPlaceholder($placeholder, $statements)
     {
         foreach ($this->cacheStack as $cache) {
             $cache->dynamicPlaceholders[$placeholder] = $statements;//添加动态内容占位符
         }
         $this->dynamicPlaceholders[$placeholder] = $statements;//给当前视图添加动态内容占位符
     }

     /**
      * Evaluates the given PHP statements. 给定的PHP语句的值
      * This method is mainly used internally to implement dynamic content feature.内部使用实现动态内容功能
      * @param string $statements the PHP statements to be evaluated. PHP语句进行计算
      * @return mixed the return value of the PHP statements. PHP语句的值
      */
     public function evaluateDynamicContent($statements)
     {
         return eval($statements);
     }

     /**
      * 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. 数据块标识
      * @param boolean $renderInPlace whether to render the block content in place. 是否渲染块内容。
      * Defaults to false, meaning the captured block will not be displayed.
      * @return Block the Block widget instance 数据块部件实例
      */
     public function beginBlock($id, $renderInPlace = false)
     {
         return Block::begin([
             'id' => $id,//数据块唯一标识
             'renderInPlace' => $renderInPlace,//是否显示标识
             'view' => $this,
         ]);
     }

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

     /**
      * Begins the rendering of content that is to be decorated by the specified view.
      * 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:
      * 开始指定的view渲染内容，用来实现嵌套布局，传入的第一个参数为布局文件的路径
      * ~~~
      * <?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.布局文件的路径或路径别名。
      * @param array $params the variables (name => value) to be extracted and made available in the decorative view.
      * 可以在视图中运用的参数
      * @return ContentDecorator the ContentDecorator widget instance 部件实例
      * @see ContentDecorator
      */
     public function beginContent($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.
      * If not, it will start caching and would expect an [[endCache()]]
      * call to end the cache and save the content into cache.
      * 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
      * A typical usage of fragment caching is as follows,
      *
      * ~~~
      * if ($this->beginCache($id)) {
      *     // ...generate content here
      *     $this->endCache();
      * }
      * ~~~
      *
      * @param string $id a unique ID identifying the fragment to be cached.缓存片段的唯一标识
      * @param array $properties initial property values for [[FragmentCache]]初始属性[FragmentCache]
      * @return boolean whether you should generate the content for caching. 是否生成缓存的内容。
      * False if the cached version is available.
      */
     public function beginCache($id, $properties = [])
     {
         $properties['id'] = $id;    //片段标识
         $properties['view'] = $this;    //调用初始化属性
         /* @var $cache FragmentCache */
         $cache = FragmentCache::begin($properties);
         if ($cache->getCachedContent() !== false) {
             $this->endCache();//从缓存中读取到了缓存的内容，则渲染内容并返回 false，不再进行缓存

             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
      */
     public function beginPage()
     {
         ob_start(); //打开输出缓冲
         ob_implicit_flush(false);//关闭缓冲区

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

     /**
      * Marks the ending of a page. 页面结束标记
      */
     public function endPage()
     {
         $this->trigger(self::EVENT_END_PAGE);
         ob_end_flush();//关闭输出缓冲区
     }