观察者模式有时也被称作发布/订阅模式，该模式用于为对象实现发布/订阅功能：一旦主体对象状态发生改变，与之关联的观察者对象会收到通知，并进行相应操作。
将一个系统分割成一个一些类相互协作的类有一个不好的副作用，那就是需要维护相关对象间的一致性。我们不希望为了维持一致性而使各类紧密耦合，这样会给维护、扩展和重用都带来不便。观察者就是解决这类的耦合关系的。
消息队列系统、事件都使用了观察者模式。
PHP 为观察者模式定义了两个接口：SplSubject 和 SplObserver。SplSubject 可以看做主体对象的抽象，SplObserver 可以看做观察者对象的抽象，要实现观察者模式，只需让主体对象实现 SplSubject ，观察者对象实现 SplObserver，并实现相应方法即可。
示例1
//下面两个接口，在php已经有了，直接implements即可，
interface IObserver
{
function onChanged( $sender, $args );
}
interface IObservable
{
function addObserver( $observer );
}
class UserList implements IObservable
{
private $_observers = array();
public function addCustomer( $name )
{
foreach( $this->_observers as $obs )
$obs->onChanged( $this, $name );
}
public function addObserver( $observer )
{
$this->_observers []= $observer;
}
}
class UserListLogger implements IObserver
{
public function onChanged( $sender, $args )
{
echo( "'$args' added to user list\n" );
}
}
$ul = new UserList();
$ul->addObserver( new UserListLogger());
$ul->addCustomer( "Jack" );
示例2
使用了php中的 SplSubject,SplObserver 主体对象和观察者对象类
// User.php 被观察主体对象
<?php
namespace DesignPatterns\Behavioral\Observer;
/**
* 观察者模式 : 被观察对象 (主体对象)
*
* 主体对象维护观察者列表并发送通知
*
*/
class User implements \SplSubject
{
/**
* user data
*
* @var array
*/
protected $data = array();
/**
* observers
*
* @var \SplObjectStorage
*/
protected $observers;
public function __construct()
{
$this->observers = new \SplObjectStorage();
}
/**
* 附加观察者
*
* @param \SplObserver $observer
*
* @return void
*/
public function attach(\SplObserver $observer)
{
$this->observers->attach($observer);
}
/**
* 取消观察者
*
* @param \SplObserver $observer
*
* @return void
*/
public function detach(\SplObserver $observer)
{
$this->observers->detach($observer);
}
/**
* 通知观察者方法
*
* @return void
*/
public function notify()
{
/** @var \SplObserver $observer */
foreach ($this->observers as $observer) {
$observer->update($this);
}
}
/**
*
* @param string $name
* @param mixed $value
*
* @return void
*/
public function __set($name, $value)
{
$this->data[$name] = $value;
// 通知观察者用户被改变
$this->notify();
}
}
// UserObserver.php // 观察者
namespace DesignPatterns\Behavioral\Observer;
/**
* UserObserver 类（观察者对象）
*/
class UserObserver implements \SplObserver
{
/**
* 观察者要实现的唯一方法
* 也是被 Subject 调用的方法
*
* @param \SplSubject $subject
*/
public function update(\SplSubject $subject)
{
echo get_class($subject) . ' has been updated';
}
}
// 测试
namespace DesignPatterns\Behavioral\Observer\Tests;
use DesignPatterns\Behavioral\Observer\UserObserver;
use DesignPatterns\Behavioral\Observer\User;
/**
* ObserverTest 测试观察者模式
*/
class ObserverTest extends \PHPUnit_Framework_TestCase
{
protected $observer;
protected function setUp()
{
$this->observer = new UserObserver();
}
/**
* 测试通知
*/
public function testNotify()
{
$this->expectOutputString('DesignPatterns\Behavioral\Observer\User has been updated');
$subject = new User();
$subject->attach($this->observer);
$subject->property = 123;
}
/**
* 测试订阅
*/
public function testAttachDetach()
{
$subject = new User();
$reflection = new \ReflectionProperty($subject, 'observers');
$reflection->setAccessible(true);
/** @var \SplObjectStorage $observers */
$observers = $reflection->getValue($subject);
$this->assertInstanceOf('SplObjectStorage', $observers);
$this->assertFalse($observers->contains($this->observer));
$subject->attach($this->observer);
$this->assertTrue($observers->contains($this->observer));
$subject->detach($this->observer);
$this->assertFalse($observers->contains($this->observer));
}
/**
* 测试 update() 调用
*/
public function testUpdateCalling()
{
$subject = new User();
$observer = $this->getMock('SplObserver');
$subject->attach($observer);
$observer->expects($this->once())
->method('update')
->with($subject);
$subject->notify();
}
}
官方demo
使用了SplObjectStorage 这个对象，这个对象本身有attach ,detach 的方法，如果不用，可以参考第二个
class MyObserver1 implements SplObserver {
public function update(SplSubject $subject) {
echo __CLASS__ . ' - ' . $subject->getName();
}
}
class MyObserver2 implements SplObserver {
public function update(SplSubject $subject) {
echo __CLASS__ . ' - ' . $subject->getName();
}
}
class MySubject implements SplSubject {
private $_observers;
private $_name;
public function __construct($name) {
$this->_observers = new SplObjectStorage();
$this->_name = $name;
}
public function attach(SplObserver $observer) {
$this->_observers->attach($observer);
}
public function detach(SplObserver $observer) {
$this->_observers->detach($observer);
}
public function notify() {
foreach ($this->_observers as $observer) {
$observer->update($this);
}
}
public function getName() {
return $this->_name;
}
}
$observer1 = new MyObserver1();
$observer2 = new MyObserver2();
$subject = new MySubject("test");
$subject->attach($observer1);
$subject->attach($observer2);
$subject->notify();
一个报纸和订阅者的例子，很像发布和订阅
/**
* Subject,that who makes news
*/
class Newspaper implements \SplSubject{
private $name;
private $observers = array();
private $content;
public function __construct($name) {
$this->name = $name;
}
//add observer
public function attach(\SplObserver $observer) {
$this->observers[] = $observer;
}
//remove observer
public function detach(\SplObserver $observer) {
$key = array_search($observer,$this->observers, true);
if($key){
unset($this->observers[$key]);
}
}
//set breakouts news
public function breakOutNews($content) {
$this->content = $content;
$this->notify();
}
public function getContent() {
return $this->content." ({$this->name})";
}
//notify observers(or some of them)
public function notify() {
foreach ($this->observers as $value) {
$value->update($this);
}
}
}
/**
* Observer,that who recieves news
*/
class Reader implements SplObserver{
private $name;
public function __construct($name) {
$this->name = $name;
}
public function update(\SplSubject $subject) {
echo $this->name.' is reading breakout news <b>'.$subject->getContent().'</b><br>';
}
}
$newspaper = new Newspaper('Newyork Times');
$allen = new Reader('Allen');
$jim = new Reader('Jim');
$linda = new Reader('Linda');
//add reader
$newspaper->attach($allen);
$newspaper->attach($jim);
$newspaper->attach($linda);
//remove reader
$newspaper->detach($linda);
//set break outs
$newspaper->breakOutNews('USA break down!');
