wordpress - 如何在 WordPress 中获取自定义主题的子菜单？

Question

我正在 WordPress 上定制它们。我正在尝试在那里获取子菜单我已通过外观添加子菜单->菜单但子菜单未显示在菜单上

if (has_nav_menu('header-menu')) {
                    wp_nav_menu([
                        'theme_location'  => 'header-menu',
                        'container'       => '',
                        'menu_class'      => 'navbar-nav ml-auto navlinks',
                        'fallback_cb'     => false,
                        'depth'           => 1,
                        'walker'          => new Guru_Header_Nav_Walker()
                    ]);
                }

类 Custom_Header_Nav_Walker()

class Custom_Header_Nav_Walker extends Walker_Nav_Menu {

    public function start_lvl( &$output, $depth = 0, $args = null ) {
        $output .= '<ul>';
    }

    public function start_el( &$output, $item, $depth = 0, $args = null, $id = 0 ) {

        $classes = '';
        if( $item->object_id == get_the_ID() ||
            ( $item->object_id == 543 && is_author() )
        ) {
            $classes .= ' active';
        }

        $output .= '<li id="id_'.$item->object_id.'" class="nav-item nav-mainlinks '.$classes.'">';
        $output .= $args->before;
        $output .= '<a class="nav-link" href="'. $item->url .'">';
        $output .= $args->link_before . $item->title . $args->link_after;
        $output .= '</a>';
        $output .= $args->after;
    }

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

    public function end_lvl( &$output, $depth = 0, $args = null ) {
        $output .= '</ul>';
    }

}