php设计模式 Observer(观察者模式)

<?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 
* 插件系统 
*/ 
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 ");