<?php

//定义接口,观察者统一的方法,便于subject调用通知
interface Observerable
{
    public function update();
}

//定义观察者1
class Observer1 implements Observerable
{
    public function update()
    {
        echo "我是观察者1";
    }

}

//定义观察者2
class Observer2 implements Observerable
{
    public function update()
    {
        echo "我是观察者2";
    }

}

// 主题,被观察的目标
class Subject
{
    private $observer_list = array();

    // 注册观察者
    public function reg_observer($observer)
    {
        if(!in_array($observer,$this->observer_list)) {
            $this->observer_list[] = $observer;
        }
    }

    // 向观察者发送消息,告诉它主题有改变
    public function notify()
    {
        if(!empty($this->observer_list)) {
            foreach($this->observer_list as $ob) {
                $ob->update();
            }
        }
    }
}

$ob1 = new Observer1();
$ob2 = new Observer2();
$subj = new Subject();
// 注册观察者
$subj->reg_observer($ob1);
$subj->reg_observer($ob2);
// 向观察者推送消息
$subj->notify();