Ejemplo de patron observer

<?php
abstract class Observable{
    protected $observers;
    function __construct(){
        $this->observers = array();
    }

    public function registrarObserver($observer){
        if(!in_array($observer, $this->observers)){
            $this->observers[] = $observer;
        }
    }

    public function deregistrarObserver($observer){
        if(in_array($observer, $this->observers)){
            $key = array_search($observer, $this->observers);
            unset($this->observers[$key]);
        }
    }

    abstract public function notificarObservers();

}

interface Observer{
    public function notificar($sender, $params);
}

class MiObservable extends Observable{

    public function __construct(){
        parent::__construct();
    }

    public function notificarObservers(){
        foreach ($this->observers as $observer) {
            $observer->notificar($this, $this->param);
        }
    }

    public function Evento($texto){
        $this->param = $texto;
        $this->notificarObservers();
    }
}

class Log implements Observer{
    public function notificar($sender, $param){
        echo get_class($sender)." envio $param a las ".date('h:i:s', time())."<br />";
    }
}

class SalvarLog implements Observer{
    public function notificar($sender, $param){
        echo "Guardando en BD $param enviado por ".get_class($sender)."... <br /><br />";
    }

}

$obj = new MiObservable();
$obj->registrarObserver(new Log());
$obj->registrarObserver(new SalvarLog());

$obj->Evento('Test 1');
sleep(1);
$obj->Evento('Test 2');

$obj->deregistrarObserver(new SalvarLog());
$obj->Evento('Test 3');
  ?>

Observe Your Object

    <?php
    class Log
    {
      public function message( $sender, $messageType, $data )
      {
        print $messageType." - ".$data."\n";
      }
    }
    class SubscriptionList
    {
      var $list = array();
      public function add( $obj, $method )
    {
        $this->list []= array( $obj, $method );
    }
    public function invoke()
    {
      $args = func_get_args();
      foreach( $this->list as $l ) { call_user_func_array( $l, $args ); }
    }
  }
  class CustomerList
  {
    public $listeners;
    public function CustomerList()
    {
      $this->listeners = new SubscriptionList();
    }
    public function addUser( $user )
    {
      $this->listeners->invoke( $this, "add", "$user" );
    }
  }
  $l = new Log();
  $cl = new CustomerList();
  $cl->listeners->add( $l, 'message' );
  $cl->addUser( "starbuck" );
  ?>