static function instance( $viewMode, $type = self::TYPE_STANDARD )
    {
        if ( $type == self::TYPE_STANDARD )
            $instance =& $GLOBALS["eZCollaborationView"][$viewMode];
        else if ( $type == self::TYPE_GROUP )
            $instance =& $GLOBALS["eZCollaborationGroupView"][$viewMode];
        else
        {
            return null;
        }
        if ( !isset( $instance ) )
        {
            $instance = new eZCollaborationViewHandler( $viewMode, $type );
        }
        return $instance;
    }