protected function _notifyListeners( $action, $value = null )
	{
		if( isset( $this->_listeners[$action] ) )
		{
			foreach( $this->_listeners[$action] as $key => $listener )
			{
				if( $listener->update( $this, $action, $value ) === false ) {
					return false;
				}
			}
		}

		return true;
	}