yii2源码学习笔记(五）

Event是所有事件类的基类。它封装了与事件相关的参数。

yii2\base\Event.php

 <?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.
  *
  * 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.
  * Event是所有事件类的基类。 它封装了与事件相关的参数。 sender属性指的是谁发起来的事件。
  * handled属性指的是事件的处理方式. 如果一个事件处理程序设置了handled为true，其它未处理的事件处理程序将不会被调用。
  * Additionally, when attaching an event handler, extra data may be passed
  * and be available via the [[data]] property when the event handler is invoked.
  * 当附加事件处理程序时，可能会通过额外的数据 ，当事件处理程序被调用时，可通过[ data]属性提供。
  * @author Qiang Xue <qiang.xue@gmail.com>
  * @since 2.0
  */
 class Event extends Object
 {
     /**
      * 事件的名字,通过[[Component::trigger()]] 和 [[trigger()]]方法设置，事件处理程序可以使用此属性来检查它的处理事件。
      * @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.
      */
     public $name;
     /**
      * 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，属性为空
      * @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.
      */
     public $sender;
     /**
      * 如果一个事件处理程序设置了handled为true，其它未处理的事件处理程序将不会被执行。
      * @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.
      */
     public $handled = false;
     /**
      * 附加一个事件处理程序时通过[[Component::on()]]传入data，且对应当前执行的事件处理程序
      * @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.
      */
     public $data;
     /**
      *存储所有的 event，所有的 event 对象/类都共用这一数据
      * @var array
      */
     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.
      * 当一个类级别事件触发，将调用该类和所有父类的事件处理程序。
      * For example, the following code attaches an event handler to `ActiveRecord`'s
      * `afterInsert` event:
      *
      * ~~~
      * 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.
      * 该处理程序是将每一个成功的[[ActiveRecord]]插入调用。
      * For more details about how to declare an event handler, please refer to [[Component::on()]].
      *
      * @param string $class the fully qualified class name to which the event handler needs to attach.
      * 定义的类级别的对象或者类名称.
      * @param string $name the event name.  事件名
      * @param callable $handler the event handler.  事件处理程序
      * @param mixed $data the data to be passed to the event handler when the event is triggered.
      * When the event handler is invoked, this data can be accessed via [[Event::data]].
      * 当事件被触发时，将传递给事件处理程序的数据。当调用事件处理程序时，该数据可以通过[[Event::data]]传递
      * @param boolean $append whether to append new event handler to the end of the existing
      * handler list. If false, the new handler will be inserted at the beginning of the existing
      * handler list.是否将新事件处理程序附加到现有的处理程序列表的结尾。如果false，新的处理程序将被插入到现有的处理程序列表开头
      * @see off()
      */
     public static function on($class, $name, $handler, $data = null, $append = true)
     {
         // 去掉 class 最左边的反斜杠
         $class = ltrim($class, '\\');
         if ($append || empty(self::$_events[$name][$class])) {
             //如果 append 为true，附加到$_events中名字为 $name 的数组结尾。如果false，被插入列表开头
             self::$_events[$name][$class][] = [$handler, $data];
         } else {
             array_unshift(self::$_events[$name][$class], [$handler, $data]);
         }
     }

     /**
      * Detaches an event handler from a class-level event.
      *
      * This method is the opposite of [[on()]].
      * [[on()]]的反方法，移除一个类的事件
      * @param string $class the fully qualified class name from which the event handler needs to be detached.
      * 定义类级别的对象或者类名称.
      * @param string $name the event name.  事件名
      * @param callable $handler the event handler to be removed.    事件处理程序
      * If it is null, all handlers attached to the named event will be removed. 如果是null，移除所有相关事件
      * @return boolean whether a handler is found and detached. 一个处理程序是否被发现且分离。
      * @see on()
      */
     public static function off($class, $name, $handler = null)
     {
        // 去掉最左边的反斜线
         $class = ltrim($class, '\\');
         if (empty(self::$_events[$name][$class])) {
             return false; // 该事件不存在，返回false
         }
         if ($handler === null) {
             // 如果 $handler 为空，该类下该所有是这个名字的事件移除，
             unset(self::$_events[$name][$class]);
             return true;//移除标记
         } else {
             $removed = false;//移除标记
             foreach (self::$_events[$name][$class] as $i => $event) {
                 // 如果 $handler 不为空，循环 $_events 找到相应的 $handler，只移除这个 $handler 和 data 组成的数组
                 if ($event[0] === $handler) {
                     unset(self::$_events[$name][$class][$i]);
                     $removed = true;//移除标记
                 }
             }
             if ($removed) {// 移除成功，使数组重新变成一个自然数组
                 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 同时检测父类
      * @param string|object $class the object or the fully qualified class name specifying the class-level event.
      * 定义类级别的对象或者类名称.
      * @param string $name the event name.  事件名
      * @return boolean whether there is any handler attached to the event. 是否有处理程序连接到事件
      */
     public static function hasHandlers($class, $name)
     {
         if (empty(self::$_events[$name])) {
             return false; //如果不存在事件，返回false
         }
         if (is_object($class)) {
             //如果是对象，获取类名
             $class = get_class($class);
         } else {
             //如果是类名，去掉左边的反斜杠
             $class = ltrim($class, '\\');
         }
         do {// 如果类中找不到，就去父类中找，直到找到或者没有父类了为止，返回true
             if (!empty(self::$_events[$name][$class])) {
                 return true;
             }
         } while (($class = get_parent_class($class)) !== false);

         return false;
     }

     /**
      * Triggers a class-level event.    触发类级别事件。
      * This method will cause invocation of event handlers that are attached to the named event
      * for the specified class and all its parent classes.该方法将调用指定类中的事件处理程序
      * @param string|object $class the object or the fully qualified class name specifying the class-level event.
      * 定义的类级别的对象或者类名称.
      * @param string $name the event name.  事件名
      * @param Event $event the event parameter. If not set, a default [[Event]] object will be created.
      * 事件参数，未设置则默认创建
      */
     public static function trigger($class, $name, $event = null)
     {
         if (empty(self::$_events[$name])) {
             return;//如果事件为空，直接返回
         }
         if ($event === null) {
              // 事件不存在，就创建一个静态 Event 对象
             $event = new static;
         }
         $event->handled = false;//事件是否被处理标志，默认未处理
         $event->name = $name;//事件名

         if (is_object($class)) {
             if ($event->sender === null) {
                 // 如果 $class 是个对象，并且sender为空，就将 $class赋给sender，即$class发起事件
                 $event->sender = $class;
             }
             $class = get_class($class);//获取类名
         } else {
             $class = ltrim($class, '\\');//不是对象，去掉左边的反斜线
         }
         do {// 循环类的 $_event，直到遇到 $event->handled 为真或者没有父类了为止
             if (!empty(self::$_events[$name][$class])) {//找到符合条件的类
                 foreach (self::$_events[$name][$class] as $handler) {
                      // 将参数赋到 event 对象的 data 属性上
                     $event->data = $handler[1];
                     // 调用 $handler 方法
                     call_user_func($handler[0], $event);
                     if ($event->handled) {
                        // 事件处理程序handled为true，其它未处理的事件处理程序将不会被调用。
                         return;
                     }
                 }
             }
         } while (($class = get_parent_class($class)) !== false);
     }
 }