Head First-观察者模式，headfirst-观察者

<?php
//使用接口，类必须实现几个功能注册，删除，通知这几个动作
interface Subject{
	public function registerObserver(Observer $o);
	public function removeObserver(Observer $o);
	public function notifyObservers();
}
interface Observer{
	public function update($a,$b,$c);
}
//各个面板不同将改行为以接口实现
interface DisplayElement{
	public function display();
}

class Weather implements Subject{
	public $observers;
	public $changed=false;
	public $a;
	public $b;
	public $c;

	public function __construct(){
		$this->observers = array();
	}
	public function registerObserver(Observer $o){
		$this->observers[] = $o;
	}
	public function removeObserver(Observer $o){
		$key = array_search($o,$this->observers);
		if($key!==false){
			unset($this->observers[$key]);
		}
	}
	public function notifyObserver(){
		if($this->changed){
			foreach($this->observer as $ob){
				$ob->update($this->a,$this->b,$this->c);
			}
		}
	}
	public function setChanged(){
		$this->changed = true;
	}
	//当数值改变时通知各个观察者
	public function measurementsChanged(){
		$this->setChanged();
		$this->notifyObserver();
	}

	public function setMeasurements($a,$b,$c){
		$this->a = $a;
		$this->b = $b;
		$this->c = $c;
		$this->measurementsChanged();		
	}
}

class CurrentConditionsDisplay implements Observer, DisplayElement{
	public $a;
	public $b;
	public $c;
	public $subject;

	public function __construct(Subject $weather){
		$this->subject = $weather;
		$this->subject->registerObserver($this);
	}

	public function update($a,$b,$c){
		$this->a = $a;
		$this->b = $b;
		$this->c = $c;
		$this->display();
	}

	public function display(){
		echo $this->a.$this->b.$this->c;
	}
}
?>