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In the second example I am going to use Standard PHP Library (SPL) to notify all attendees about the party location change. SPL has 2 interfaces and a Class for Observer.

• interface SplObserver
• Had update($subject) method
• interface SplSubject
• Has attach($observer) method
• Has detach($observer) method
• Has notify() method
• class SplObjectStorage

Here is our BirthdayParty class that implements SplSubject interface.

<?php
/**
 *  @name BirthdayParty
 *  @author Gaurav Jassal
 *  @access public
 *  @copyright gauravjassal@gmail.com
 *
 */

class BirthdayParty implements SplSubject {

    protected $party_location = "Oxford Street";

    protected $observers = array();

	/**
	 * Add the observer to the list
	 * @param SplObserver $observer
	 * @return void
	 */
    public function attach(SplObserver $observer) {
        $this->observers[] = $observer;
    }
    /**
     * Remove observer for the list
     * @param SplObserver $observer
     * @return
     */
    public function detach(SplObserver $observer) {
    	// we are not going to remove any observer in this example
    }

	/**
	 * Send notification the observer
	 * @return void
	 */
    public function notify() {
        foreach ($this->observers as $key=>$value) {
            $value->update($this);
        }
    }
	/**
	 * Getter function for party location
	 * @return string
	 */
    public function getPartyLocation() {
        return $this->party_location;
    }
	/**
	 * Setter function for party location
	 * @param string $party_location
	 * @return void
	 */
    public function setPartyLocation($party_location) {
        $this->party_location = $party_location;
		$this->notify();
    }
}
?>

Our second Attendee class that implements SplObserver. When ever there is a change in the party location the update method gets triggered.

<?php

class Attendes implements SplObserver{
	protected $id;

	public function __construct($id)
	{
		$this->id = $id;
	}

	public function update(SplSubject $s)
	{
		echo "<br> " . $this->id . " has been notified about the new location :  " . $s->getPartyLocation();
		//return;
	}
}
?>

Usage

<?php
	error_reporting(E_ALL);
	ini_set("display_errors", 1); 

	require_once('BirthdayParty.php');
	require_once('Attendes.php');
	echo "<h1>Eample 2 </h1>";
	$bp = new BirthdayParty();

	$bp->attach(new Attendes("Gaurav"));
	$bp->attach(new Attendes("Ronnie"));
	$bp->attach(new Attendes("Katie"));
	$bp->attach(new Attendes("Suman"));
	$bp->attach(new Attendes("Devang"));

	$bp->setPartyLocation("King Williams St.");

?>

Results
Eample 2

Gaurav has been notified about the new location : King Williams St.
Ronnie has been notified about the new location : King Williams St.
Katie has been notified about the new location : King Williams St.
Suman has been notified about the new location : King Williams St.
Devang has been notified about the new location : King Williams St.

2 Responses to “Observer pattern in PHP part 2”

1. julian says:

   November 11, 2009 at 5:43 pm

   Interesting post.

   You have mentioned the SplObjectStorage class but I can’t see where you use it in your example. Shouldn’t it be used for the BirthdayParty::observers property ? (Instead of array.)
2. Gaurav Jassal says:

   November 12, 2009 at 6:47 am

   @Julian: You are right with SPL example we can use SplObjectStorage class. I checked the example file that you sent me the usage look straight forward.

   I will include you sample code in this post.

   Thanks, Gaurav