namespace yii\base;

 use Yii;
 use yii\helpers\FileHelper;
 use yii\widgets\Block;
 use yii\widgets\ContentDecorator;
 use yii\widgets\FragmentCache;

 /**
  * View represents a view object in the MVC pattern.
  *
  * View provides a set of methods (e.g. [[render()]]) for rendering purpose.
  * 视图提供了一套渲染页面的方法（例如[render()]）
  *
  * @property string|boolean $viewFile The view file currently being rendered. False if no view file is being
  * rendered. This property is read-only.
  *
  * @author Qiang Xue <qiang.xue@gmail.com>
  * @since 2.0
  */
 class View extends Component
 {
     /**
      * @event Event an event that is triggered by [[beginPage()]].
      * beginPage事件名常量，被[beginPage()]触发
      */
     const EVENT_BEGIN_PAGE = 'beginPage';
     /**
      * @event Event an event that is triggered by [[endPage()]].
      * endPage事件名常量，被[endPage()]触发
      */
     const EVENT_END_PAGE = 'endPage';
     /**
      * @event ViewEvent an event that is triggered by [[renderFile()]] right before it renders a view file.
      * beforeRender事件名常量，被[renderFile()]触发
      */
     const EVENT_BEFORE_RENDER = 'beforeRender';
     /**
      * @event ViewEvent an event that is triggered by [[renderFile()]] right after it renders a view file.
      * afterRender事件名常量，被[renderFile()]触发
      */
     const EVENT_AFTER_RENDER = 'afterRender';

     /**
      * @var ViewContextInterface the context under which the [[renderFile()]] method is being invoked.
      */
     public $context;
     /**
      * @var mixed custom parameters that are shared among view templates.
      * 在视图模板*享的自定义参数
      */
     public $params = [];
     /**
      * @var array a list of available renderers indexed by their corresponding supported file extensions.
      * Each renderer may be a view renderer object or the configuration for creating the renderer object.
      * 一个可用的渲染索引列表。每个渲染器是一个渲染器对象或创建渲染对象配置数组
      * For example, the following configuration enables both Smarty and Twig view renderers:
      * 下面的配置数组同时支持 Smarty 和 Twig
      *
      * ```php
      * [
      *     'tpl' => ['class' => 'yii\smarty\ViewRenderer'],
      *     'twig' => ['class' => 'yii\twig\ViewRenderer'],
      * ]
      * ```
      *
      * If no renderer is available for the given view file, the view file will be treated as a normal PHP
      * and rendered via [[renderPhpFile()]].
      * 如果没有值，则
      */
     public $renderers;
     /**
      * @var string the default view file extension. This will be appended to view file names if they don't have file extensions.
      * 默认视图文件扩展名，在视图文件没有扩展名的情况下自动添加
      */
     public $defaultExtension = 'php';
     /**
      * @var Theme|array|string the theme object or the configuration for creating the theme object.
      * If not set, it means theming is not enabled.
      * 主题对象或创建主题对象的配置
      */
     public $theme;
     /**
      * @var array a list of named output blocks. The keys are the block names and the values
      * are the corresponding block content. You can call [[beginBlock()]] and [[endBlock()]]
      * to capture small fragments of a view. They can be later accessed somewhere else
      * through this property.
      * 一个输出块列表。键是块名称值为相应的块内容。你可以调用 [ beginblock() ]和[ endblock() ]捕获视图的small fragments
      * 它们可以在其他地方通过这个属性访问。
      */
     public $blocks;
     /**
      * @var array a list of currently active fragment cache widgets. This property
      * is used internally to implement the content caching feature. Do not modify it directly.
      * 当前active fragment缓存小部件的列表。此属性用于内部实现内容缓存功能。不要直接修改它。
      * @internal
      */
     public $cacheStack = [];
     /**
      * @var array a list of placeholders for embedding dynamic contents. This property
      * is used internally to implement the content caching feature. Do not modify it directly.
      * 一种嵌入动态内容占位符列表。此属性用于内部实现内容缓存功能。不要直接修改它。
      * @internal
      */
     public $dynamicPlaceholders = [];

     /**
      * @var array the view files currently being rendered. There may be multiple view files being
      * rendered at a moment because one view may be rendered within another.
      * 目前正在渲染的视图文件。可能有多个视图文件被渲染，因为一个视图可以在另一个视图中呈现
      */
     private $_viewFiles = [];

     /**
      * Initializes the view component.
      * 初始化视图组件
      */
     public function init()
     {
         parent::init();//调用父类的init方法
         if (is_array($this->theme)) {//如果theme是数组
             if (!isset($this->theme['class'])) {//且没有设置类名
                 $this->theme['class'] = 'yii\base\Theme';//则类名为'yii\base\Theme'
             }
             //以配置的形式创建对象
             $this->theme = Yii::createObject($this->theme);
         } elseif (is_string($this->theme)) {//否则以字符串参数的形式创建
             $this->theme = Yii::createObject($this->theme);
         }
     }

     /**
      * Renders a view.
      * 渲染一个视图
      * The view to be rendered can be specified in one of the following formats:
      * 被渲染的视图可以用下列方式指定
      *
      * - path alias (e.g. "@app/views/site/index");
      *   路径别名
      * - absolute path within application (e.g. "//site/index"): the view name starts with double slashes.
      *   The actual view file will be looked for under the [[Application::viewPath|view path]] of the application.
      *   绝对路径，将会在[Application::viewPath|view path]下查找文件
      * - absolute path within current module (e.g. "/site/index"): the view name starts with a single slash.
      *   The actual view file will be looked for under the [[Module::viewPath|view path]] of the [[Controller::module|current module]].
      *   模块下的绝对路径，将会在[Module::viewPath|view path]下查找文件
      * - relative view (e.g. "index"): the view name does not start with `@` or `/`. The corresponding view file will be
      *   looked for under the [[ViewContextInterface::getViewPath()|view path]] of the view `$context`.
      *   相对路径，将会在[ViewContextInterface::getViewPath()|view path]下查找文件
      *   If `$context` is not given, it will be looked for under the directory containing the view currently
      *   being rendered (i.e., this happens when rendering a view within another view).
      *
      * @param string $view the view name.
      * @param array $params the parameters (name-value pairs) that will be extracted and made available in the view file.
      * @param object $context the context to be assigned to the view and can later be accessed via [[context]]
      * in the view. If the context implements [[ViewContextInterface]], it may also be used to locate
      * the view file corresponding to a relative view name.
      * @return string the rendering result
      * @throws InvalidParamException if the view cannot be resolved or the view file does not exist.
      * @see renderFile()
      */
     public function render($view, $params = [], $context = null)
     {
         //查找视图文件路径
         $viewFile = $this->findViewFile($view, $context);
         //调用renderFile()渲染视图文件
         return $this->renderFile($viewFile, $params, $context);
     }