<?phpnamespace 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.     * 觸發事件的對象     */    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.     * 記錄事件是否已被處理，當 handled 被設置為 true 時，執行到這個 event 的時候，會停止，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;    /**     * 存儲所有的 event，因為是 static 的屬性，所有的 event 對象/類都共享這一份數據     */    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()]].     *     * 為一個類添加事件     *     * @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 最左邊的斜杠        $class = ltrim($class, '//');        // 如果 append 為true，就放到 $_events 中名字為 $name 的數組的最后，否則放到最前面        if ($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()]].     *     * 移除一個類的事件     *     * @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][$class])) {            // 不存在該事件            return false;        }        if ($handler === null) {            // 如果 handler 為空，直接將在該類下該事件移除，即移出所有的是這個名字的事件            unset(self::$_events[$name][$class]);            return true;        } else {            $removed = false;            // 如果 $handler 不為空，循環 $_events 找到相應的 handler，只移除這個 handler 和 data 組成的數組            foreach (self::$_events[$name][$class] as $i => $event) {                if ($event[0] === $handler) {                    unset(self::$_events[$name][$class][$i]);                    $removed = true;                }            }            if ($removed) {                // 移除之后，使數組重新變成一個自然數組                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.     * 檢測在某個類或者對象是否具有某個事件     * @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)) {            // 如果是一個 object，就獲取其類名            $class = get_class($class);        } else {            // 如果是一個類名，就去掉 class 最左邊的斜杠            $class = ltrim($class, '//');        }        // 如果該類中找不到，就去父類中找，直到找到或者沒有父類了為止        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.     * 觸發某個類或者對象的某個事件     * @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，就創建一個 Event 對象            $event = new static;        }        // 設置event對象的屬性，默認是未被處理的        $event->handled = false;        $event->name = $name;        if (is_object($class)) {            if ($event->sender === null) {                // 如果 $class 是個對象，并且是 sender 為空，就將 $class 賦給 sender，即 $class 就是觸發事件的對象                $event->sender = $class;            }            $class = get_class($class);        } else {            $class = ltrim($class, '//');        }        // 循環類的 $_event，直到遇到 $event->handled 為真或者沒有父類了為止        do {            if (!empty(self::$_events[$name][$class])) {                foreach (self::$_events[$name][$class] as $handler) {                    // 將參數賦到 event 對象的 data 屬性上                    $event->data = $handler[1];                    // 調用 $handler 方法                    // 在方法中，可以用 $this->data 取到相應的參數                    // 也可以在其中設置 $this->handled 的值，中斷后續事件的觸發                    call_user_func($handler[0], $event);                    // 當某個 handled 被設置為 true 時，執行到這個事件的時候，會停止，并忽略剩下的事件                    if ($event->handled) {                        return;                    }                }            }        } while (($class = get_parent_class($class)) !== false);    }}

[    'add' => [        'Child' => [            [function ($event) { ... }, $data],            [[$object, 'handleAdd'], null],            [['ChildClass', 'handleAdd'], $data],            ['handleAdd', $data]        ],        'ChildClass' => [            ...        ]    ],    'delete' => [        ...    ]]