设计模式-观察者

用途总结：观察者模式可以将某个状态的变化立即通知所有相关的对象，并调用对像的处理方法。

实现总结：需要一个观察者类来处理变化，被观察的对象需要实现通知所有观察者的方法。

<?php
 /**
  * 观察者模式
  * 
  * 定义对象间的一种一对多的依赖关系,以便当一个对象的状态发生改变时,所有依赖于它的对象都得到通知并自动刷新
  * 能够便利地创建查看目标对象状态的对象,并且提供与核心对象非耦合的指定功能
  * 
 */
 class Observerable
 {
     private $_observers=array();
 
     public function registerObserver($observer)
     {
         $this->_observers[] =$observer;
     }
 
     public function removeObserver($observer)
     {
         $key=array_search($observer,$this->_observers);
         if(!($key===false))
         {
             unset($this->_observers[$key]);
         }
     }
 
     public function notifyObservers()
     {
         foreach($this->_observers as $observer)
         {
             if($observer instanceof Observer) $observer->update($this);
         }
     }
 }
 
 interface Observer
 {
     public function update($observer);
 }
 
 interface DisplayElement
 {
     public function display();
 }
 
 // -- 实例类定义
 class NewsObserverable extends Observerable
 {
     private $_sports_news;
     public function setSportsNews($data)
     {
         $this->_sports_news =$data;
         $this->notifyObservers();
     }
 
     public function getSportsNews()
     {
         return $this->_sports_news;
     }
 
     private $_local_news;
     public function setLocalNews($data)
     {
         $this->_local_news =$data;
         $this->notifyObservers();
     }
 
     public function getLocalNews()
     {
         return $this->_local_news;
     }
 }
 
 class SportsNews implements Observer,DisplayElement
 {
     private $_data=null;
     public function update($observer)
     {
         if($this->_data !=$observer->getSportsNews())
         {
             $this->_data =$observer->getSportsNews();
             $this->display();
         }
     }
 
     public function display()
     {
         echo $this->_data.date("Y-m-d H:i:s")."<br/>";
     }
 }
 
 class LocalNews implements Observer,DisplayElement
 {
     private $_data=null;
     public function update($observer)
     {
         if($this->_data !=$observer->getLocalNews())
         {
             $this->_data =$observer->getLocalNews();
             $this->display();
         }
     }
 
     public function display()
     {
         echo $this->_data.date("Y-m-d H:i:s")."<br/>";
     }
 }
 
 // -- 实例化 ---
 
 $objObserver=new NewsObserverable();
 $local=new LocalNews();
 $sports=new SportsNews();
 
 $objObserver->registerObserver($local);
 $objObserver->registerObserver($sports);
 
 $objObserver->setSportsNews("sports news 1 ");
 $objObserver->setLocalNews("local news 1 ");
 $objObserver->removeObserver($sports);
 $objObserver->setLocalNews("local news 2 ");
 $objObserver->setSportsNews("sports news 2 ");
 $objObserver->removeObserver($local);
 $objObserver->setLocalNews("local news 3 ");