观察者模式

/**
observer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
*/
//主角
    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//具体主角
    {
        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->setSportsNews("sports news 2 ");

$objObserver->setLocalNews("local news 1 ");
$objObserver->setLocalNews("local news 2 ");
$objObserver->setLocalNews("local news 3 ");

$objObserver->removeObserver($sports);
$objObserver->removeObserver($local);

参考文章 https://wenku.baidu.com/view/b4c78b4702768e9951e738fb.html