yii2阅读随笔13

下面我们来看一下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.
 * 事件是所有事件类的基础。
 * It encapsulates the parameters associated with an event.
 * The [[sender]] property describes who raises the event.
 * 它封装了与事件相关的参数 
 * And the [[handled]] property indicates if the event is handled.
 * 属性指示事件处理。
 *
 * Additionally, when attaching an event handler, extra data may be passed
 * and be available via the [[data]] property when the event handler is invoked.
 * 此外，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
{
    /**
     * @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
     * 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 = [];
    /**
     * 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.
     * 返回一个值，该值指示是否有任何处理程序附加到指定的类级别事件。 
     * 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[$name])) {
            // 不存在，直接返回false
            return false;
        }
        if (is_object($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;
    }