如何在wordpress中自定义wp-bootstrap-navwalker

<?php
class WP_Bootstrap_Navwalker extends Walker_Nav_Menu {
    public function start_lvl(&$output, $depth = 0, $args = array()) {
        $indent = str_repeat("\t", $depth);
        $output .= "\n$indent<ul class=\"dropdown-menu\">\n";
    }
 
    public function start_el(&$output, $item, $depth = 0, $args = array(), $id = 0) {
        $indent = ($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_ancestor) ? 'active' : '';
        $classes[] = 'menu-item-' . $item->ID;
 
        $class_names = join(' ', apply_filters('nav_menu_css_class', array_filter($classes), $item, $args));
        $class_names = ' class="' . esc_attr($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' . $id . $value . $class_names . $li_attributes . '>';
 
        $attributes = !empty($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) . '"' : '';
 
        $attributes .= ($args->walker->has_children) ? ' class="dropdown-toggle" data-toggle="dropdown"' : '';
 
        $item_output = $args->before;
        $item_output .= '<a' . $attributes . '>';
        $item_output .= $args->link_before . apply_filters('the_title', $item->title, $item->ID) . $args->link_after;
        $item_output .= ($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);
    }
 
    public function display_element($element, &$children_elements, $max_depth, $depth = 0, $args, &$output) {
        if (!$element) {
            return;
        }
 
        $id_field = $this->db_fields['id'];
 
        if (is_object($args[0])) {
            $args[0]->has_children = !empty($children_elements[$element->$id_field]);
        }
 
        parent::display_element($element, $children_elements, $max_depth, $depth, $args, $output);
    }
}
?>

require_once get_template_directory() . '/wp-bootstrap-navwalker/wp_bootstrap_navwalker.php';

function register_my_menu() {
    register_nav_menu('primary', 'Primary Menu');
}
add_action('after_setup_theme', 'register_my_menu');

<?php
wp_nav_menu(array(
    'theme_location' => 'primary',
    'depth' => 2,
    'container' => 'div',
    'container_class' => 'collapse navbar-collapse',
    'container_id' => 'bs-example-navbar-collapse-1',
    'menu_class' => 'nav navbar-nav',
    'fallback_cb' => 'WP_Bootstrap_Navwalker::fallback',
    'walker' => new WP_Bootstrap_Navwalker(),
));
?>