Yii源码阅读笔记（八）

前面阅读了Yii2的两个基本类Object和Component，了解了Yii的三个重要概念属性、事件、行为，下面开始阅读Event类，Event类是所有事件类的基类：

 <?php
 /**
  * @link http://www.yiiframework.com/
  * @copyright Copyright (c) 2008 Yii Software LLC
  * @license http://www.yiiframework.com/license/
  */

 namespace yii\base;

 /**
  * Event is the base class for all event classes.
  * Event 是所有事件类的基类，是对Component的深化
  *
  * It encapsulates the parameters associated with an event.
  * The [[sender]] property describes who raises the event.
  * And the [[handled]] property indicates if the event is handled.
  * If an event handler sets [[handled]] to be true, the rest of the
  * uninvoked handlers will no longer be called to handle the event.
  *
  * Additionally, when attaching an event handler, extra data may be passed
  * and be available via the [[data]] property when the event handler is invoked.
  *
  * @author Qiang Xue <qiang.xue@gmail.com>
  * @since 2.0
  */
 class Event extends Object
 {
     /**
      * @var string the event name. This property is set by [[Component::trigger()]] and [[trigger()]].
      * Event handlers may use this property to check what event it is handling.
      * 事件的名字，通过[[Component::trigger()]] 和 [[trigger()]]方法设置，事件处理程序通过这个属性类检查处理的事件
      */
     public $name;
     /**
      * @var object the sender of this event. If not set, this property will be
      * set as the object whose "trigger()" method is called.
      * This property may also be a `null` when this event is a
      * class-level event which is triggered in a static context.
      *
      * 触发事件的对象，如果未设置，则设置为调用"trigger()"方法的对象，如果是在静态环境下触发的类级别的事件，怎为空
      */
     public $sender;
     /**
      * @var boolean whether the event is handled. Defaults to false.
      * When a handler sets this to be true, the event processing will stop and
      * ignore the rest of the uninvoked event handlers.
      *
      * 记录事件是否已被处理，当 handled 被设置为 true 时，执行到这个 event 的时候，会停止，并忽略剩下的 event
      */
     public $handled = false;
     /**
      * @var mixed the data that is passed to [[Component::on()]] when attaching an event handler.
      * Note that this varies according to which event handler is currently executing.
      * 事件加载时传入的数据，对应当前执行的事件处理程序
      */
     public $data;

     /**
      * @var array contains all globally registered event handlers.
      * 存储所有的 event，因为是 static 的属性，所有的 event 对象/类都共享这一份数据
      */
     private static $_events = [];

     /**
      * Attaches an event handler to a class-level event.
      * 为一个类添加事件
      *
      * When a class-level event is triggered, event handlers attached
      * to that class and all parent classes will be invoked.
      *
      * For example, the following code attaches an event handler to `ActiveRecord`'s
      * `afterInsert` event:
      *
      * ```php
      * Event::on(ActiveRecord::className(), ActiveRecord::EVENT_AFTER_INSERT, function ($event) {
      *     Yii::trace(get_class($event->sender) . ' is inserted.');
      * });
      * ```
      *
      * The handler will be invoked for EVERY successful ActiveRecord insertion.
      *
      * For more details about how to declare an event handler, please refer to [[Component::on()]].
      *
      * @param string|object $class 定义的类级别的对象或者类名称.
      * @param string $name 事件名
      * @param callable $handler 事件处理程序.
      * @param mixed $data 数据.
      * When the event handler is invoked, this data can be accessed via [[Event::data]].
      * @param boolean $append whether to append new event handler to the end of the existing
      * handler list. If false, the new handler will be inserted at the beginning of the existing
      * handler list.
      * @see off()
      */
     public static function on($class, $name, $handler, $data = null, $append = true)
     {
          // 去掉 class 最左边的斜线
         $class = ltrim($class, '\\');
         if ($append || empty(self::$_events[$name][$class])) {
             // 如果 append 为true，就放到 $_events 中名字为 $name 的数组的最后
             self::$_events[$name][$class][] = [$handler, $data];
         } else {
             //否则放到最前面
             array_unshift(self::$_events[$name][$class], [$handler, $data]);
         }
     }

     /**
      * Detaches an event handler from a class-level event.
      * [[on()]]方法的反方法，移除一个类的事件
      * This method is the opposite of [[on()]].
      *
      * @param string|object $class 定义的类级别的对象或者类名称.
      * @param string $name 事件名
      * @param callable $handler 事件处理程序.
      * If it is null, all handlers attached to the named event will be removed.
      * @return boolean whether a handler is found and detached.
      * @see on()
      */
     public static function off($class, $name, $handler = null)
     {
         // 去掉 class 最左边的斜线
         $class = ltrim($class, '\\');
         if (empty(self::$_events[$name][$class])) {
             // 如果不存在该事件，返回false
             return false;
         }
         if ($handler === null) {
             // 如果 handler 为空，也就是没有规定移除的事件处理程序，直接将该事件移除，即移出所有的是这个名字的事件
             unset(self::$_events[$name][$class]);
             return true;
         } else {
             $removed = false; //移除标记
             // 如果 $handler 不为空，遍历 $_events 找到相应的 handler，只移除这个 handler 和 data 组成的数组
             foreach (self::$_events[$name][$class] as $i => $event) {
                 if ($event[0] === $handler) {
                     unset(self::$_events[$name][$class][$i]);
                     $removed = true;
                 }
             }
             if ($removed) {
                 //如果删除成功，调用array_values方法重新赋值，初始化索引
                 self::$_events[$name][$class] = array_values(self::$_events[$name][$class]);
             }

             return $removed;
         }
     }

     /**
      * Returns a value indicating whether there is any handler attached to the specified class-level event.
      * Note that this method will also check all parent classes to see if there is any handler attached
      * to the named event.
      * 检测在某个类或者对象是否具有某个事件/会同时检测父类
      *
      * @param string|object $class 定义的类级别的对象或者类名称.
      * @param string $name 事件名
      * @return boolean whether there is any handler attached to the event.
      */
     public static function hasHandlers($class, $name)
     {
         if (empty(self::$_events[$name])) {
              //如果不存在，直接返回false
             return false;
         }
         if (is_object($class)) {
             // 如果是一个 object，就获取其类名  get_class 内置函数，用于获取对象的方法
             $class = get_class($class);
         } else {
              // 如果是一个类名，就去掉 class 最左边的斜杠
             $class = ltrim($class, '\\');
         }
         //将该类/该对象对应的类的父类以及该类/该对象对应的类实现的接口名称合并到一个数组中
         $classes = array_merge(
             [$class],
             class_parents($class, true),//获取父类的类名
             class_implements($class, true)//获取当前类和父类实现的所有接口类名
         );
         //判断是否存在事件处理程序，存在返回true
         foreach ($classes as $class) {
             if (!empty(self::$_events[$name][$class])) {
                 return true;
             }
         }

         return false;
     }

     /**
      * Triggers a class-level event.
      * This method will cause invocation of event handlers that are attached to the named event
      * for the specified class and all its parent classes.
      * 触发某个类或者对象的某个事件/会同时作用于父类
      *
      * @param string|object $class 定义的类级别的对象或者类名称.
      * @param string $name 事件名
      * @param Event $event the event parameter. If not set, a default [[Event]] object will be created.
      */
     public static function trigger($class, $name, $event = null)
     {
         if (empty(self::$_events[$name])) {
             //如果事件不存在，直接返回
             return;
         }
         if ($event === null) {
              // 构建Event对象，为传入到handler函数中做准备
             $event = new static;
         }
         $event->handled = false;//事件是否被处理标志
         $event->name = $name;//事件名

         if (is_object($class)) {
             if ($event->sender === null) {
                 // 如果 $class 是个对象，并且是 sender 为空，就将 $class 赋给 sender，即 $class 就是触发事件的对象
                 $event->sender = $class;
             }
             $class = get_class($class);//取得类名称
         } else {
             $class = ltrim($class, '\\');//去掉类名称左边的斜线
         }
         //将该类/该对象对应的类的父类以及该类/该对象对应的类实现的接口名称合并到一个数组中
         $classes = array_merge(
             [$class],
             class_parents($class, true),
             class_implements($class, true)
         );

         foreach ($classes as $class) {//遍历所有的类
             if (!empty(self::$_events[$name][$class])) {//找到符合条件的类
                 foreach (self::$_events[$name][$class] as $handler) {
                     $event->data = $handler[1];//设置data数据
                     call_user_func($handler[0], $event);//调用处理程序
                     if ($event->handled) {//事件是否被处理标志为真，结束执行
                         return;
                     }
                 }
             }
         }
     }
 }