PHP 高级编程(3)

PHP 高级编程(3)

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)