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
    }