Définition
Le design pattern observer définit une relation un-à-plusieurs entre des objets de sorte que quand un objet change d'état, toutes ses relations sont notifiées et mises à jour automatiquement.
Diagramme UML
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| Diagramme de classes du design pattern observer |
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Exemple en PHP
Depuis PHP 5.1, la Standard PHP Library (SPL) fournit les interfaces
SplSubject et
SplObserver pour implémenter le design pattern observer.
class Subject implements SplSubject
{
private $observers = array();
private $variable;
public function attach(SplObserver $observer)
{
$id = spl_object_hash($observer);
$this->observers[$id] = $observer;
}
public function detach(SplObserver $observer)
{
$id = spl_object_hash($observer);
unset($this->observers[$id]);
}
public function getVariable()
{
return $this->variable;
}
public function notify()
{
foreach ($this->observers as $observer) {
$observer->update($this);
}
}
public function setVariable($value)
{
$this->variable = $value;
$this->notify();
}
}
class ConcreteObserverA implements SplObserver
{
public function update(SplSubject $subject)
{
echo 'ConcreteObserverA received: ' . $subject->getVariable() . "\n";
}
}
class ConcreteObserverB implements SplObserver
{
public function update(SplSubject $subject)
{
echo 'ConcreteObserverB received: ' . $subject->getVariable() . "\n";
}
}
$subject = new Subject();
$subject->attach(new ConcreteObserverA());
$subject->attach(new ConcreteObserverB());
$subject->setVariable(42);
L'exemple affiche :
ConcreteObserverA received: 42
ConcreteObserverB received: 42
