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 ");