PHP 高级编程(3/5) - 使用SPL(标准PHP库)实现观察者模式

SPL（标准PHP库 - Standard PHP Library）是PHP5面向对象功能中重要的部分。原文解释是这样的“The Standard PHP Library (SPL) is a collection of interfaces and classes that are meant to solve common problems”。

SplSubject 和 SplObserver 接口

The SplSubject interface is used alongside SplObserver to implement the Observer Design Pattern.

观察者模式是一种简单的事件系统，包含了两个或更多的互相交互的类。这一模式允许某个类观察另一个类的状态，当被观察类的状态发生变化时，这个模式会得到通知。被观察的类叫subject，负责观察的类叫做Observer 。PHP 提供的 SplSubject 和 SplObserver接口可用来表达这些内容。

SplSubject {

/* 方法 */

abstract public void attach ( SplObserver $observer )

abstract public void detach ( SplObserver $observer )

abstract public void notify ( void )

}

SplObserver {

/* 方法 */

abstract public void update ( SplSubject $subject )

}

这里，splsubject类维护了一个特定状态，当这个状态发生变化时，他就会调用notify方法，所以之前使用attach注册的splobserver实例的update就会被调用。这里我们实现一个简单地观察者模式的例子

<?php

/**

 * 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!');

//=====output======

//Allen is reading breakout news USA break down! (Newyork Times)

//Jim is reading breakout news USA break down! (Newyork Times)

上例中我们通过数组存储 observer对象，使用数组及可能会出现两个问题:

1、同一个observer可能会被加载多次，导致多次调用同一个对象的update方法。

2、detach中需要通过迭代或者搜索数组来找到要删除的observer对象，导致运行效率降低。

SplObjectStorage类

PHP5提供了SplObjectStorage类，在这里我们可以用来存储observer对象，SplObjectStoraged的实例就像一个数组，但是他所存放的对象是唯一的。SplObjectStorage还可以使用detach直接从集合中删除指定的对象而不用遍历或搜索整个集合。下面看一个SplObjectStorage的例子：

<?php

 $ObjectStorage = new SplObjectStorage();

 class classa

 {

     #code...

 }

 class classb

 {

    #code...

 }

$a = new classa();

$b = new classb();

$ObjectStorage->attach($a);

$ObjectStorage->attach($b);

$ObjectStorage->attach($a);

foreach ($ObjectStorage as $key => $item) {

    echo ($key+).'、'.(new ReflectionClass($item))->getName()."\n";

}

//output

1、classa
2、classb
[Finished in 0.1s]

?>

上例中我们可以看到，在ObjectStorage这个集合中只有1个calssa，尽管我们添加了两次。并且冲集合中删除一个元素也变得极为简单，拿上面的代码来说，只需使用$ObjectStorage->attach($a);即可轻松的将$a从集合中移除。

结合 SplObjectStorage 我们再来修改最上面那个观察者模式的例子

<?php

/**

 * Subject,that who makes news

 */

class Newspaper implements \SplSubject{

    private $name;

    private $observers;

    private $content;

    public function __construct($name) {

        $this->name = $name;

        $this->observers = new SplObjectStorage();

    }

    //add observer

    public function attach(\SplObserver $observer) {

        $this->observers -> attach($observer);

    }

    //remove observer

    public function detach(\SplObserver $observer) {

        $this->observers -> detach($observer);

    }

    //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 $this->name.' is reading breakout news '.$subject->getContent()."\n";

    }

}

$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!');

//=====output======

//Allen is reading breakout news USA break down! (Newyork Times)

//Jim is reading breakout news USA break down! (Newyork Times)

巴特西

PHP 高级编程(3/5) - 使用SPL(标准PHP库)实现观察者模式

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