Introduction
The Observer pattern is like a newspaper subscription. You have a subject , which is the object that changes its state (in our example is the newspaper) and a observer , which is the object that receives these changes (the subscriber).
Implementing the Observer Pattern
First I'll create the subject interface.
php interface Subject {
public function registerObserver( Observer $o ) ;
public function removeObserver( Observer $o ) ;
public function notifyObservers( ) ;
} observer interface.
php interface Observer {
public function update( $news ) ;
} Newspaper class which implements the Subject interface.
php class Newspaper implements Subject {
private $observers = array ( ) ;
private $news ;
public function __construct( ) {
}
public function registerObserver( Observer $o ) {
$this ->observers [ ] = $o ;
}
public function removeObserver( Observer $o ) {
unset ( $this ->observers [ array_search ( $o , $this ->observers ) ] ) ;
}
public function notifyObservers( ) {
foreach ( $this ->observers as $observer ) {
$observer ->update ( $this ->news ) ;
}
}
public function setNewNews( $news ) {
$this ->news = $news ;
$this ->notifyObservers ( ) ;
}
} Subscriber class which implements the Observer interface.
php class Subscriber implements Observer {
private $newspaper ;
public function __construct( Subject $newspaper ) {
$this ->newspaper = $newspaper ;
$this ->newspaper ->registerObserver ( $this ) ;
}
public function cancelSubscript( ) {
$this ->newspaper ->removeObserver ( $this ) ;
}
public function update( $news ) {
echo date ( "h:i:s" ) . ": " . $news ;
}
}
php $newspaper = new Newspaper( ) ;
$subscriber1 = new Subscriber( $newspaper ) ;
$subscriber2 = new Subscriber( $newspaper ) ;
$newspaper ->setNewNews ( "Today is tuesday." ) ;
$newspaper ->setNewNews ( "So, tomorrow will be wednesday." ) ;
$subscriber1 ->cancelSubscript ( ) ;
$newspaper ->setNewNews ( "So, the day after tomorrow will be thursday." ) ; Conclusion
You can put another classes that implements Observer and all of them will receive the last news!
