使用Wordpress Nav-walker类在下拉列表的第一个<li>之前添加标题<li>

class Custom_Nav_Walker extends Walker_Nav_Menu {
    function start_lvl(&$output, $depth = 0, $args = array()) {
        $indent = str_repeat("\t", $depth);
        $output .= "\n$indent<ul class=\"sub-menu\">\n";
    }

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

        $classes = empty($item->classes) ? array() : (array) $item->classes;
        $class_names = join(' ', apply_filters('nav_menu_css_class', array_filter($classes), $item, $args));
        $class_names = $class_names ? ' class="' . esc_attr($class_names) . '"' : '';

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

        // 添加标题<li>
        if ($depth === 0) {
            $output .= '<li class="menu-title">标题</li>';
        }

        $attributes = !empty($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;
        $item_output .= ($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);
    }
}

<?php
wp_nav_menu(array(
    'theme_location' => 'primary',
    'menu_class' => 'nav-menu',
    'walker' => new Custom_Nav_Walker(),
));
?>