php設計模式 觀察者模式，設計模式觀察者

觀察者模式的核心是把客戶元素（觀察者）從一個中心類（主體）中分離開來。當主體知道事件發(fā)生時，觀察者需要被通知到。同時，我們并不希望將主體與觀察者之間的關系進行硬編碼。為了達到這個目的，我們可以允許觀察者在主體上進行注冊。

觀察者模式實現(xiàn)了低耦合、非侵入式的通知與更新機制。

場景：當一個事件發(fā)生后，要執(zhí)行一連串更新操作。

<span>EventGenerator</span>.php

<?<span>php
namespace Baobab;
</span><span>/*</span><span>*
 * Class EventGenerator 基類，事件發(fā)生者
 </span><span>*/</span>
<span>abstract</span> <span>class</span><span> EventGenerator{

    </span><span>//</span><span>觀察者對于事件發(fā)生者是不可見的，事件發(fā)生者不關心有哪些觀察者關注了事件</span>
    <span>private</span> <span>$observers</span> = <span>array</span><span>();

    </span><span>/*</span><span>*
     * 添加觀察者
     </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>*
     *逐個通知觀察者進行更新的操作
     </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 觀察者，觀察的對象是事件發(fā)生者
 * @package Baobab
 </span><span>*/</span>
<span>interface</span><span> Observer{
    </span><span>/*</span><span>*
     * @param null $event_info  事件的信息
     * 表示事件發(fā)生后進行更新的操作
     </span><span>*/</span>
    <span>function</span> update(<span>$event_info</span> = <span>null</span><span>);
}</span>

index.php

<span>class</span> Event <span>extends</span><span> \Baobab\EventGenerator{
    </span><span>/*</span><span>*
     *觸發(fā)一個新的事件
     </span><span>*/</span>
    <span>function</span><span> trigger(){
        </span><span>echo</span> 'Event發(fā)生'<span>;
        </span><span>$this</span>-><span>notify();
    }
}

</span><span>/*</span><span>*
 * 觀察者1
 </span><span>*/</span>
<span>class</span> Observer1 <span>implements</span><span> \Baobab\Observer{
    </span><span>function</span> Update(<span>$event_info</span> = <span>null</span><span>){
        </span><span>echo</span> '更新操作代碼1'<span>;
    }
}<br />
<span>/*<span>* <br /> * 觀察者2 <br /><span> */</span></span></span>
</span><span>class</span> Observer2 <span>implements</span><span> \Baobab\Observer{
    </span><span>function</span> Update(<span>$event_info</span> = <span>null</span><span>){
        </span><span>echo</span> '更新操作代碼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();

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