Walker Nav Menü, Dropdown ermitteln

class myHeader extends Walker_Nav_Menu {
        function start_el(&$output, $item, $depth = 0, $args = array(), $id = 0) {
            //Add attributes to link element.
            $attributes     =  !empty($item->attr_title)    ? ' title="'    . esc_attr($item->attr_title)   . '"' : '';
            $attributes     .= !empty($item->target)        ? ' target="'   . esc_attr($item->target)       . '"' : '';
            $attributes     .= !empty($item->xfn)           ? ' rel="'      . esc_attr($item->xfn)          . '"' : '';
            $attributes     .= !empty($item->url)           ? ' href="'     . esc_attr($item->url)          . '"' : '';
            
            $liAttributes   = " class='";
            $liAttributes   .= ($item->current)              ? "active"                                 : "";           
            $liAttributes   .= "'";
            
            $liID           = ($item->object_id)            ? " id='menu-item-". $item->object_id . "'"         : "";
            
            $output .= "<li " . $liID . " ". $liAttributes . ">";
                $output .= "<a" . $attributes . ">";
                    $output .= $args->link_before . apply_filters("the_title", $item->title, $item->ID) . $args->link_after;
                $output .= "</a>";
       }




       function end_el(&$output, $item, $depth = 0, $args = array()) {
           $output .= "</li>";
           $output .= '';
       }




    }