Yii2的深入学习--yii\base\Event 类
根据之前一篇文章，我们知道 Yii2 的事件分两类，一是类级别的事件，二是实例级别的事件。类级别的事件是基于 yii\base\Event 实现，实例级别的事件是基于 yii\base\Component 实现。
今天先来看下类级别事件的实现，代码是 yii\base\Event 类。
<?php namespace yii\base; /** * Event is the base class for all event classes. */ 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 */ 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 */ 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. */ public $data; /** * 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 $_events = []; /** * Attaches an event handler to a class-level event. * * When a class-level event is triggered, event handlers attached * to that class and all parent classes will be invoked. * * For example, the following code attaches an event handler to `ActiveRecord`'s * `afterInsert` event: * * ~~~ * Event::on(ActiveRecord::className(), ActiveRecord::EVENT_AFTER_INSERT, function ($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()]]. * * 为一个类添加事件 * * @param string $class the fully qualified class name to which the event handler needs to attach. * @param string $name the event name. * @param callable $handler the event handler. * @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]]. * @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 最左边的斜杠 $class = ltrim($class, '\\'); // 如果 append 为true，就放到 $_events 中名字为 $name 的数组的最后，否则放到最前面 if ($append || empty(self::$_events[$name][$class])) { self::$_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()]]. * * 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. * @param string $name the event name. * @param callable $handler the event handler to be removed. * If it is null, all handlers attached to the named event will be removed. * @return boolean whether a handler is found and detached. * @see on() */ public static function off($class, $name, $handler = null) { $class = ltrim($class, '\\'); if (empty(self::$_events[$name][$class])) { // 不存在该事件 return false; } if ($handler === null) { // 如果 handler 为空，直接将在该类下该事件移除，即移出所有的是这个名字的事件 unset(self::$_events[$name][$class]); return true; } else { $removed = false; // 如果 $handler 不为空，循环 $_events 找到相应的 handler，只移除这个 handler 和 data 组成的数组 foreach (self::$_events[$name][$class] as $i => $event) { if ($event[0] === $handler) { unset(self::$_events[$name][$class][$i]); $removed = true; } } if ($removed) { // 移除之后，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 * @param string|object $class the object or the fully qualified class name specifying the class-level event. * @param string $name the event name. * @return boolean whether there is any handler attached to the event. */ public static function hasHandlers($class, $name) { if (empty(self::$_events[$name])) { // 不存在，直接返回 return false; } if (is_object($class)) { // 如果是一个 object，就获取其类名 $class = get_class($class); } else { // 如果是一个类名，就去掉 class 最左边的斜杠 $class = ltrim($class, '\\'); } // 如果该类中找不到，就去父类中找，直到找到或者没有父类了为止 do { if (!empty(self::$_events[$name][$class])) { return true; } } while (($class = get_parent_class($class)) !== false); 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 * @param string|object $class the object or the fully qualified class name specifying the class-level event. * @param string $name the event name. * @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[$name])) { return; } if ($event === null) { // 事件不存在，就创建一个 Event 对象 $event = new static; } // 设置event对象的属性，默认是未被处理的 $event->handled = false; $event->name = $name; if (is_object($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); } else { $class = ltrim($class, '\\'); } // 循环类的 $_event，直到遇到 $event->handled 为真或者没有父类了为止 do { if (!empty(self::$_events[$name][$class])) { 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 // 在方法中，可以用 $this->data 取到相应的参数 // 也可以在其中设置 $this->handled 的值，中断后续事件的触发 call_user_func($handler[0], $event); // 当某个 handled 被设置为 true 时，执行到这个事件的时候，会停止，并忽略剩下的事件 if ($event->handled) { return; } } } } while (($class = get_parent_class($class)) !== false); } }
通过上面代码可以看出，类级别的 Event，其本质就是在 Event 类中的 $_events 变量中存储事件，触发事件的时候，只需将其取出，执行即可。
$_events里面的数据结构大概如下：
[ 'add' => [ 'Child' => [ [function ($event) { ... }, $data], [[$object, 'handleAdd'], null], [['ChildClass', 'handleAdd'], $data], ['handleAdd', $data] ], 'ChildClass' => [ ... ] ], 'delete' => [ ... ] ]
之后讲到yii\base\Component类时，我们会再来说一下实例级别的事件。
对 Yii2 源码有兴趣的同学可以关注项目 yii2-2.0.3-annotated，现在在上面已经添加了不少关于 Yii2 源码的注释，之后还会继续添加～
有兴趣的同学也可以参与进来，提交 Yii2 源码的注释。
