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About Me
- Name: Nigel Fernandes
- Location: Panjim, Goa, India
Crazy, dancing, programming, Goan.. I'm a computer geek and proud to be one. I program in Java, Ruby and .Net, PHP, Javascript. A lot of my recent work has been about CSS and UI design practices for large scale websites and Agile teams. I still while away hours dreaming up a web startup.
Implementing the Observer Design Pattern with PHP
Saturday, March 01, 2008
If you, like me need to implement a light weight Observer framework within your PHP project, and really do not need PEAR's Event_Dispatcher, look no further. ;-)Below is my light weight implementation of a Observer pattern for PHP.
interface Observerable {
public function attach(Observer $observer);
public function detach(Observer $observer);
public function notify();
}
interface Observer {
public function update(Payload $payload);
}
class Payload {
public $data;
public function __construct($data) {
$this->data = $data;
}
}
class Watched implements Observerable {
private $state;
private $watchers;
public function __construct(){
$this->watchers = Array();
}
public function attach (Observer $observer) {
if (array_search($observer, $this->watchers, true) === false) {
$this->watchers[] = $observer;
}
}
public function detach (Observer $observer) {
$observerOffset = array_search($observer, $this->watchers, true);
if ($observerOffset !== false) {
unset($this->watchers[$observerOffset]);
}
}
public function notify () {
foreach ($this->watchers as $observer) {
$observer->update(new Payload($this->state));
}
}
public function changeState($newState) {
$this->state = $newState;
$this->notify();
}
}
class Watcher implements Observer {
public function update (Payload $payload) {
echo $payload->data;
}
}
// Create Objects
$watched = new Watched();
$watcher1 = new Watcher();
$watcher2 = new Watcher();
// Attach Watchers
$watched->attach($watcher1);
$watched->attach($watcher2);
// Change State of Watched
$state = "foo";
$watched->changeState($state); // Causes "foo" to be printed from within Watcher1 & Watcher2
// Remove a Watcher
$watched->detach($watcher1);
$watched->changeState($state); // Causes "foo" to be printed from within Watcher1
I tend to use a slightly different naming system for most my classes. Apart from that, this small snippet of code is pretty much a standard Observer pattern implementation. Very useful when you are writing small scale PHP applications (like a Facebook App. for example).I also tend to favor the use of a small container class for passing data into the watchers, but of course since this is PHP, you could probably just use a complex array instead.
Labels: Design Patterns, Facebook PHP application, Observer Pattern, PHP
