设计模式(19)observer模式

abstract class Subject{
  protected $observers;
  public function attach(Observer $m){
      $this->observers[] = $m;
  }
  public function detach(Observer $m){
     unset($this->observers[array_search($m,$this->observers)]);
  }
  public function notify(){
    foreach($this->observers as $item){
      $item->Update();
    }
  }
}
class ConcreteSubject extends Subject{
  protected $subjectState;
  public function __construct(){
    $this->observers = [];
  }
  public function setState($o){
    $this->subjectState = $o;
  }
  public function getState(){
    return $this->subjectState;
  }
}
abstract class  Observer {
  public abstract function update();
}
class ConcreteObserver extends Observer{
  private $observerState;
  private $subject;
  public function __construct($subject){
    $this->subject = $subject;
  }
  public function update(){
    $this->observerState =  $this->subject->getState();
    echo "Subjectstate has  modified".", now :".$this->observerState;
  }

}
//测试代码
$subject = new ConcreteSubject();
$observers = new ConcreteObserver($subject);
$subject->attach($observers);
$subject->setState('sate1');
$subject->notify();