Yii源码阅读笔记（八）

  1 <?php
  2 /**
  3  * @link http://www.yiiframework.com/
  4  * @copyright Copyright (c) 2008 Yii Software LLC
  5  * @license http://www.yiiframework.com/license/
  6  */
  7 
  8 namespace yii\base;
  9 
 10 /**
 11  * Event is the base class for all event classes.
 12  * Event 是所有事件类的基类，是对Component的深化
 13  * 
 14  * It encapsulates the parameters associated with an event.
 15  * The [[sender]] property describes who raises the event.
 16  * And the [[handled]] property indicates if the event is handled.
 17  * If an event handler sets [[handled]] to be true, the rest of the
 18  * uninvoked handlers will no longer be called to handle the event.
 19  *
 20  * Additionally, when attaching an event handler, extra data may be passed
 21  * and be available via the [[data]] property when the event handler is invoked.
 22  *
 23  * @author Qiang Xue <qiang.xue@gmail.com>
 24  * @since 2.0
 25  */
 26 class Event extends Object
 27 {
 28     /**
 29      * @var string the event name. This property is set by [[Component::trigger()]] and [[trigger()]].
 30      * Event handlers may use this property to check what event it is handling.
 31      * 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
 32      */
 33     public $name;
 34     /**
 35      * @var object the sender of this event. If not set, this property will be
 36      * set as the object whose "trigger()" method is called.
 37      * This property may also be a `null` when this event is a
 38      * class-level event which is triggered in a static context.
 39      * 
 40      * 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
 41      */
 42     public $sender;
 43     /**
 44      * @var boolean whether the event is handled. Defaults to false.
 45      * When a handler sets this to be true, the event processing will stop and
 46      * ignore the rest of the uninvoked event handlers.
 47      * 
 48      * 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
 49      */
 50     public $handled = false;
 51     /**
 52      * @var mixed the data that is passed to [[Component::on()]] when attaching an event handler.
 53      * Note that this varies according to which event handler is currently executing.
 54      * 事件加载时传入的数据，对应当前执行的事件处理程序
 55      */
 56     public $data;
 57 
 58     /**
 59      * @var array contains all globally registered event handlers.
 60      * 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
 61      */
 62     private static $_events = [];
 63 
 64 
 65     /**
 66      * Attaches an event handler to a class-level event.
 67      * 为一个类添加事件
 68      * 
 69      * When a class-level event is triggered, event handlers attached
 70      * to that class and all parent classes will be invoked.
 71      *
 72      * For example, the following code attaches an event handler to `ActiveRecord`‘s
 73      * `afterInsert` event:
 74      *
 75      * ```php
 76      * Event::on(ActiveRecord::className(), ActiveRecord::EVENT_AFTER_INSERT, function ($event) {
 77      *     Yii::trace(get_class($event->sender) . ‘ is inserted.‘);
 78      * });
 79      * ```
 80      *
 81      * The handler will be invoked for EVERY successful ActiveRecord insertion.
 82      *
 83      * For more details about how to declare an event handler, please refer to [[Component::on()]].
 84      *
 85      * @param string|object $class 定义的类级别的对象或者类名称.
 86      * @param string $name 事件名
 87      * @param callable $handler 事件处理程序.
 88      * @param mixed $data 数据.
 89      * When the event handler is invoked, this data can be accessed via [[Event::data]].
 90      * @param boolean $append whether to append new event handler to the end of the existing
 91      * handler list. If false, the new handler will be inserted at the beginning of the existing
 92      * handler list.
 93      * @see off()
 94      */
 95     public static function on($class, $name, $handler, $data = null, $append = true)
 96     {
 97          // 去掉 class 最左边的斜线
 98         $class = ltrim($class, ‘\\‘);
 99         if ($append || empty(self::$_events[$name][$class])) {
100             // 如果 append 为true，就放到 $_events 中名字为 $name 的数组的最后
101             self::$_events[$name][$class][] = [$handler, $data];
102         } else {
103             //否则放到最前面
104             array_unshift(self::$_events[$name][$class], [$handler, $data]);
105         }
106     }
107 
108     /**
109      * Detaches an event handler from a class-level event.
110      * [[on()]]方法的反方法，移除一个类的事件
111      * This method is the opposite of [[on()]].
112      *
113      * @param string|object $class 定义的类级别的对象或者类名称.
114      * @param string $name 事件名
115      * @param callable $handler 事件处理程序.
116      * If it is null, all handlers attached to the named event will be removed.
117      * @return boolean whether a handler is found and detached.
118      * @see on()
119      */
120     public static function off($class, $name, $handler = null)
121     {
122         // 去掉 class 最左边的斜线
123         $class = ltrim($class, ‘\\‘);
124         if (empty(self::$_events[$name][$class])) {
125             // 如果不存在该事件，返回false
126             return false;
127         }
128         if ($handler === null) {
129             // 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
130             unset(self::$_events[$name][$class]);
131             return true;
132         } else {
133             $removed = false; //移除标记
134             // 如果 $handler 不为空，遍历 $_events 找到相应的 handler，只移除这个 handler 和 data 组成的数组
135             foreach (self::$_events[$name][$class] as $i => $event) {
136                 if ($event[0] === $handler) {
137                     unset(self::$_events[$name][$class][$i]);
138                     $removed = true;
139                 }
140             }
141             if ($removed) {
142                 //如果删除成功，调用array_values方法重新赋值，初始化索引
143                 self::$_events[$name][$class] = array_values(self::$_events[$name][$class]);
144             }
145 
146             return $removed;
147         }
148     }
149 
150     /**
151      * Returns a value indicating whether there is any handler attached to the specified class-level event.
152      * Note that this method will also check all parent classes to see if there is any handler attached
153      * to the named event.
154      * 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
155      * 
156      * @param string|object $class 定义的类级别的对象或者类名称.
157      * @param string $name 事件名
158      * @return boolean whether there is any handler attached to the event.
159      */
160     public static function hasHandlers($class, $name)
161     {
162         if (empty(self::$_events[$name])) {
163              //如果不存在，直接返回false
164             return false;
165         }
166         if (is_object($class)) {
167             // 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
168             $class = get_class($class);
169         } else {
170              // 如果是一个类名，就去掉 class 最左边的斜杠
171             $class = ltrim($class, ‘\\‘);
172         }
173         //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
174         $classes = array_merge(
175             [$class],
176             class_parents($class, true),//获取父类的类名
177             class_implements($class, true)//获取当前类和父类实现的所有接口类名
178         );
179         //判断是否存在事件处理程序，存在返回true
180         foreach ($classes as $class) {
181             if (!empty(self::$_events[$name][$class])) {
182                 return true;
183             }
184         }
185 
186         return false;
187     }
188 
189     /**
190      * Triggers a class-level event.
191      * This method will cause invocation of event handlers that are attached to the named event
192      * for the specified class and all its parent classes.
193      * 触发某个类或者对象的某个事件/会同时作用于父类
194      * 
195      * @param string|object $class 定义的类级别的对象或者类名称.
196      * @param string $name 事件名
197      * @param Event $event the event parameter. If not set, a default [[Event]] object will be created.
198      */
199     public static function trigger($class, $name, $event = null)
200     {
201         if (empty(self::$_events[$name])) {
202             //如果事件不存在，直接返回
203             return;
204         }
205         if ($event === null) {
206              // 构建Event对象，为传入到handler函数中做准备
207             $event = new static;
208         }
209         $event->handled = false;//事件是否被处理标志
210         $event->name = $name;//事件名
211 
212         if (is_object($class)) {
213             if ($event->sender === null) {
214                 // 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
215                 $event->sender = $class;
216             }
217             $class = get_class($class);//取得类名称
218         } else {
219             $class = ltrim($class, ‘\\‘);//去掉类名称左边的斜线
220         }
221         //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
222         $classes = array_merge(
223             [$class],
224             class_parents($class, true),
225             class_implements($class, true)
226         );
227 
228         foreach ($classes as $class) {//遍历所有的类
229             if (!empty(self::$_events[$name][$class])) {//找到符合条件的类
230                 foreach (self::$_events[$name][$class] as $handler) {
231                     $event->data = $handler[1];//设置data数据
232                     call_user_func($handler[0], $event);//调用处理程序
233                     if ($event->handled) {//事件是否被处理标志为真，结束执行
234                         return;
235                     }
236                 }
237             }
238         }
239     }
240 }