观察者模式的核心是把客户元素(观察者)从一个中心类(主体)中分离开来。当主体知道事件发生时,观察者需要被通知到。同时,我们并不希望将主体与观察者之间的关系进行硬编码。为了达到这个目的,我们可以允许观察者在主体上进行注册。
观察者模式实现了低耦合、非侵入式的通知与更新机制。
场景:当一个事件发生后,要执行一连串更新操作。
<span>EventGenerator</span>.php
<?<span>php namespace Baobab; </span><span>/*</span><span>* * Class EventGenerator 基类,事件发生者 </span><span>*/</span> <span>abstract</span> <span>class</span><span> EventGenerator{ </span><span>//</span><span>观察者对于事件发生者是不可见的,事件发生者不关心有哪些观察者关注了事件</span> <span>private</span> <span>$observers</span> = <span>array</span><span>(); </span><span>/*</span><span>* * 添加观察者 </span><span>*/</span> <span>function</span> addObserver(Observer <span>$observer</span><span>){ </span><span>$this</span>->observers[] = <span>$observer</span><span>; } </span><span>/*</span><span>* *逐个通知观察者进行更新的操作 </span><span>*/</span> <span>function</span><span> notify(){ </span><span>foreach</span>(<span>$this</span>->observers <span>as</span> <span>$observer</span><span>){ </span><span>$observer</span>-><span>update(); } } }</span>
<span>Observer</span>.php
<?<span>php namespace Baobab; </span><span>/*</span><span>* * Class Observer 观察者,观察的对象是事件发生者 * @package Baobab </span><span>*/</span> <span>interface</span><span> Observer{ </span><span>/*</span><span>* * @param null $event_info 事件的信息 * 表示事件发生后进行更新的操作 </span><span>*/</span> <span>function</span> update(<span>$event_info</span> = <span>null</span><span>); }</span>
index.php
<span>class</span> Event <span>extends</span><span> \Baobab\EventGenerator{ </span><span>/*</span><span>* *触发一个新的事件 </span><span>*/</span> <span>function</span><span> trigger(){ </span><span>echo</span> 'Event发生'<span>; </span><span>$this</span>-><span>notify(); } } </span><span>/*</span><span>* * 观察者1 </span><span>*/</span> <span>class</span> Observer1 <span>implements</span><span> \Baobab\Observer{ </span><span>function</span> Update(<span>$event_info</span> = <span>null</span><span>){ </span><span>echo</span> '更新操作代码1'<span>; } }<br /> <span>/*<span>* <br /> * 观察者2 <br /><span> */</span></span></span> </span><span>class</span> Observer2 <span>implements</span><span> \Baobab\Observer{ </span><span>function</span> Update(<span>$event_info</span> = <span>null</span><span>){ </span><span>echo</span> '更新操作代码2'<span>; } } </span><span>$event</span> = <span>new</span><span> Event(); </span><span>$event</span>->addObserver(<span>new</span><span> Observer1()); </span><span>$event</span>->addObserver(<span>new</span><span> Observer2()); </span><span>$event</span>->trigger();