选择子项时，将类添加到父项目Walker Nav Menu

Question

您好我有以下Walker Nav菜单。

class Walker_Nav_Primary extends Walker_Nav_Menu {

function start_lvl( &$output,  $depth  ) {  //ul
    $indent = str_repeat("\t", $depth); // "\t" represents the tab between lines
    $subemnu = ($depth > 0) ? ' dropdown-menu ' : '' ;
    $output .= "\n$indent <ul class=\"dropdown-menu$submenu depth_$depth\"\n> ";


}

function start_el( &$output, $item, $depth = 0,  $args = array(), $id = 0 ) { //li a span
    $indent = ($depth) ? str_repeat("\t",$depth) : '';

    $li_attributes = '' ;
    $class_names = $value = '';

    //$classes = empty( $item->classes ) ? array() : (array) $item->classes;

    $classes[] = ($args->walker->has_children) ? 'dropdown' : '';
    $classes[] = ($item->current || $item->current_item_anchestor) ? 'active' : '';
    if( ($depth > 0) && $args->walker->has_children ){
        $classes[] = 'dropdown-submenu mul';
    } 

    $class_names = join( ' ', apply_filters('nav_menu_css_class', array_filter( $classes ) )  );
    $class_names = ' class=" ' . esc_attr($class_names) .  ' " ';

    $id = apply_filters('nav_menu_item_id', 'menu-item-'.$item->ID, $item, $args);
    $id = strlen( $id ) ? ' id=" ' . esc_attr( $id ) . ' "' : '';

    $output .= $indent . '<li' . $class_names . '>';

    $attributes = ! empty( $item->attr_title ) ? ' tittle="' . esc_attr($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) . '"' : '';

    $attributes .= ($args->walker->has_children ) ? ' class="dropdown-toggle" data-toggle="dropdown"' : '';

    $item_output = $args->before;
    $item_output .= '<a tabindex="-1"' . $attributes . '>';
    $item_output .= $args->link_before . apply_filters( 'the_title', $item->title, $item-ID ) . $args->link_after;
    $item_output .= ( $depth == 0 && $args->walker->has_children ) ? ' <b class="caret"></b></a>' : '</a>';
    $item_output .= $args->after;

    $output .= apply_filters ( 'walker_nav_menu_start_el', $item_output, $item, $depth, $args  );

    }

}

我想要实现的是当选择子菜单以将活动类添加到top li时。这可以通过步行者导航菜单或通过CSS吗？我看了几个带jquery的解决方案，但我更喜欢用css或Walker Nav菜单来解决。