Code examples of PHP observer pattern

<?php
// 观察者模式

/**
 * abstract subject
 */
interface Subject
{
	/**
	 * add Observer
	 */
	public function attach(Observer $obs);
	
	/**
	 * remove Observer
	 */
	public function detach(Observer $obs);
	
	/**
	 * notify Observer
	 */
	public function notify();
}

interface Observer
{
	public function update(Subject $sub);
}

/**
 * concrete subject
 */
class ConcreteSubject implements Subject
{
	private $observerList = array();
	
	public function attach(Observer $obs) {
		$this->observerList[] = $obs;
	}
	
	public function detach(Observer $obs) {
		$this->observerList = array_diff($this->observerList, [$obs]);
	}
	
	public function notify() {
		foreach($this->observerList as $ol) {
			$ol->update($this);
		}
	}
	
	public function doAct() {
		echo &#39;DoAct ... <br/>&#39;;
		$this->notify();
	}
}

/**
 * concrete observer 1
 */
class Observer1 implements Observer
{
	public function update(Subject $sub) {
		echo &#39;Observer one updated! <br/>&#39;;
	}
}

/**
 * concrete observer 2
 */
class Observer2 implements Observer
{
	public function update(Subject $sub) {
		echo &#39;Observer two updated! <br/>&#39;;
	}
}

// test code
$sub = new ConcreteSubject();

$sub->attach(new Observer1()); //add observer
$sub->attach(new Observer1());
$sub->attach(new Observer2());

$sub->doAct();