/**

 * 当对象间存在一对多关系时，则使用观察者模式（Observer Pattern）。

 * 比如，当一个对象被修改时，则会自动通知它的依赖对象。观察者模式属于行为型模式。

 * 一个对象（目标对象）的状态发生改变，所有的依赖对象（观察者对象）都将得到通知，进行广播通知。

 */

<?php

namespace Observer;

class Subject

{

    private $state;

    private $observers = [];

    public function getState()

    {

        return $this->state;

    }

    public function seState($state)

    {

        $this->state = $state;

        $this->notifyAllObjects();

    }

    public function register(Observer $object)

    {

        $this->observers[] = $object;

    }

    public function remove($object)

    {

        foreach ($this->observers as $key => $observer) {

            if ($observer == $object){

                unset($this->observers[$key]);

            }

        }

    }

    public function notifyAllObjects()

    {

        foreach ($this->observers as $observer) {

            $observer->update();

        }

    }

}

<?php

namespace Observer;

abstract class Observer

{

    protected $subject;

    public abstract function update();

}

<?php

namespace Observer;

class ObserverA extends Observer

{

    private $myState = 'init A';

    public function __construct(Subject $subject)

    {

        $this->subject = $subject;

        $this->subject->register($this);

    }

    public function update()

    {

        $this->myState = $this->subject->getState();

    }

    public function getSate()

    {

        return "ObserverA get state:".$this->myState;

    }

}

<?php

namespace Observer;

class ObserverB extends Observer

{

    private $myState = 'init B';

    public function __construct(Subject $subject)

    {

        $this->subject = $subject;

        $this->subject->register($this);

    }

    public function update()

    {

        $this->myState = $this->subject->getState();

    }

    public function getSate()

    {

        return "ObserverB get state:".$this->myState;

    }

}

<?php

spl_autoload_register(function ($className){

    $className = str_replace('\\','/',$className);

    include $className.".class.php";

});

use Observer\ObserverA;

use Observer\ObserverB;

use Observer\Subject;

/*

ObserverA get state:init A
ObserverB get state:init B
ObserverA get state:hello
ObserverB get state:hello
*/

$subject = new Subject(); $objectA = new ObserverA($subject); $objectB = new ObserverB($subject); echo $objectA->getSate(); echo '<br/>'; echo $objectB->getSate(); echo '<br/>'; $subject->seState("hello"); echo $objectA->getSate(); echo '<br/>'; echo $objectB->getSate(); echo '<br/>';