public function detach($event, IObserver $observer)
    {
        if (!isset($this->_observers[$event])) {
            return;
        }

        foreach ($this->_observers[$event] as $key=> $attachedObserver) {
            if ($attachedObserver === $observer) {
                array_splice($this->_observers[$event], $key, 1);
            }
        }
    }