PHP 高級編程(3)

SPL（標准PHP庫 - Standard PHP Library）是PHP5面向對象功能中重要的部分。原文解釋是這樣的“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.

觀察者模式是一種簡單的事件系統，包含了兩個或更多的互相交互的類。這一模式允許某個類觀察另一個類的狀態，當被觀察類的狀態發生變化時，這個模式會得到通知。被觀察的類叫subject，負責觀察的類叫做Observer 。PHP 提供的 SplSubject 和 SplObserver接口可用來表達這些內容。

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 )
}

這裡，splsubject類維護了一個特定狀態，當這個狀態發生變化時，他就會調用notify方法，所以之前使用attach注冊的splobserver實例的update就會被調用。這裡我們實現一個簡單地觀察者模式的例子

<?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)