如何在wp实现navwalker中添加类？

Question

我使用wp-materialize-navwalker制作WordPress的素材菜单，一切正常，效果很好。

但是当我使用WordPress仪表板向li添加一个类时，它不起作用。

你可以帮我解决一下吗？这是我的wp_materialize_navwalker.php文件：

<?php

/**
 * Class Name: wp_materialize_navwalker
 * GitHub URI: #
 * Description: A custom WordPress nav walker class to "fully" implement the Materialize CSS nested navigation style in a custom theme using the WordPress manager
 * Version: 1.0.0
 * Author: Kailo - https://kailo.io
 * License: MIT
 * License URI: #
 */

class wp_materialize_navwalker extends Walker {
  var $db_fields = array( 'parent' => 'menu_item_parent', 'id' => 'db_id' );

    function start_lvl( &$output, $depth = 0, $args = array() ) {
        // Depth-dependent classes.
        $indent = ( $depth > 0  ? str_repeat( "\t", $depth ) : '' ); // code indent
        $display_depth = ( $depth + 1); // because it counts the first submenu as 0
        $classes = array(
            'dropdown-content',
            ( $display_depth % 2  ? 'menu-odd' : 'menu-even' ),
            ( $display_depth >=2 ? 'sub-sub-menu' : '' ),
            'menu-depth-' . $display_depth
        );
        $class_names = implode( ' ', $classes );

        // Build HTML for output.
        $output .= "\n" . $indent . ' class="' . $class_names . '">' . "\n";
    }

  function end_lvl( &$output, $depth = 0, $args = array() ) {
    $indent = str_repeat("\t", $depth);
    $output .= "$indent</ul>\n";
  }

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

        // Depth-dependent classes.
        $depth_classes = array(
            ( $depth == 0 ? 'main-menu-item' : 'sub-menu-item' ),
            ( $depth >=2 ? 'sub-sub-menu-item' : '' ),
            ( $depth % 2 ? 'menu-item-odd' : 'menu-item-even' ),
            'menu-item-depth-' . $depth
        );
        $depth_class_names = esc_attr( implode( ' ', $depth_classes ) );

        // Passed classes.
        $classes = empty( $item->classes ) ? array() : (array) $item->classes;
        $class_names = esc_attr( implode( ' ', apply_filters( 'nav_menu_css_class', array_filter( $classes ), $item ) ) );

    /* Add active class */
    if(in_array('current-menu-item', $classes)) {
      $classes[] = 'active';
      unset($classes['current-menu-item']);
    }

    /* Check for children */
    $children = get_posts(array(
      'post_type' => 'nav_menu_item',
      'nopaging' => true,
      'numberposts' => 1,
      'meta_key' => '_menu_item_menu_item_parent',
      'meta_value' => $item->ID
      ));

    if (!empty($children)) {
      $classes[] = 'dropdown';
    }
    $class_names = join( ' ', apply_filters( 'nav_menu_css_class', array_filter( $classes ), $item, $args ) );
    // $class_names = $class_names ? ' class="' . esc_attr( $class_names ) . '"' : '';
    // $id = apply_filters( 'nav_menu_item_id', 'menu-item-'. $item->ID, $item, $args );
    // $id = $id ? ' id="' . esc_attr( $id ) . '"' : '';
    $output     .= $indent . '<li id="nav-menu-item-'. $item->ID . '" class="' . $depth_class_names . '">';
    $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 .= ! empty( $children )         ? ' data-activates="dropdown-'. $item->ID .'"' : '';
    $attributes .= ! empty( $children )         ? ' class="dropdown-button '. $depth_class_names .'"' : '';

    $item_output .= '<a'. $attributes .'>';
    $item_output .= $args->link_before . apply_filters( 'the_title', $item->title, $item->ID ) . $args->link_after;

    if(!empty($children))
      $item_output .= '<i class="material-icons left menu_arrow">expand_more</i>';

    $item_output .= '</a>';

    $item_output .= $args->after;

    if(!empty($children))
      $item_output .= '<ul id="dropdown-'.$item->ID.'"';
    $output .= apply_filters( 'walker_nav_menu_start_el', $item_output, $item, $depth, $args );

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