当我创建一个引导式导航菜单时，我遇到了类似的问题，下拉链接都立即显示出来。我使用以下步骤更正此问题：

从github repo链接下载navwalker：https://github.com/wp-bootstrap/wp-bootstrap-navwalker

将此文件放在主题的根文件夹和函数中。php文件使用require_once get_template_directory() . \'/wp-bootstrap-navwalker.php\';

最后，您必须添加以下参数：

$defaults = array(
  \'container\' => false,
  \'theme_location\' => \'primary-menu\',
  \'menu_class\' => \'nav navbar-nav navbar-right\',
  \'fallback_cb\' => \'WP_Bootstrap_Navwalker::fallback\',
  \'walker\' => new WP_Bootstrap_Navwalker(),
);
wp_nav_menu($defaults);

我希望有帮助

<?php
/**
 * Class Name: wp_bootstrap_navwalker
 * GitHub URI: https://github.com/twittem/wp-bootstrap-navwalker
 * Description: A custom WordPress nav walker class to implement the Bootstrap 3 navigation style in a custom theme using the WordPress built in menu manager.
 * Version: 2.0.4
 * Author: Edward McIntyre - @twittem
 * License: GPL-2.0+
 * License URI: http://www.gnu.org/licenses/gpl-2.0.txt
 */
class wp_bootstrap_navwalker extends Walker_Nav_Menu {
    /**
     * @see Walker::start_lvl()
     * @since 3.0.0
     *
     * @param string $output Passed by reference. Used to append additional content.
     * @param int $depth Depth of page. Used for padding.
     */
    public function start_lvl( &$output, $depth = 0, $args = array() ) {
        $indent = str_repeat( "\\t", $depth );
        $output .= "\\n$indent<ul role=\\"menu\\" class=\\" category-list\\">\\n";
    }
    /**
     * @see Walker::start_el()
     * @since 3.0.0
     *
     * @param string $output Passed by reference. Used to append additional content.
     * @param object $item Menu item data object.
     * @param int $depth Depth of menu item. Used for padding.
     * @param int $current_page Menu item ID.
     * @param object $args
     */
    public function start_el( &$output, $item, $depth = 0, $args = array(), $id = 0 ) {
        $indent = ( $depth ) ? str_repeat( "\\t", $depth ) : \'\';
        /**
         * Dividers, Headers or Disabled
         * =============================
         * Determine whether the item is a Divider, Header, Disabled or regular
         * menu item. To prevent errors we use the strcasecmp() function to so a
         * comparison that is not case sensitive. The strcasecmp() function returns
         * a 0 if the strings are equal.
         */
        if ( strcasecmp( $item->attr_title, \'divider\' ) == 0 && $depth === 1 ) {
            $output .= $indent . \'<li role="presentation" class="divider">\';
        } else if ( strcasecmp( $item->title, \'divider\') == 0 && $depth === 1 ) {
            $output .= $indent . \'<li role="presentation" class="divider">\';
        } else if ( strcasecmp( $item->attr_title, \'dropdown-header\') == 0 && $depth === 1 ) {
            $output .= $indent . \'<li role="presentation" class="dropdown-header">\' . esc_attr( $item->title );
        } else if ( strcasecmp($item->attr_title, \'disabled\' ) == 0 ) {
            $output .= $indent . \'<li role="presentation" class="disabled"><a href="#">\' . esc_attr( $item->title ) . \'</a>\';
        } else {
            $class_names = $value = \'\';
            $classes = empty( $item->classes ) ? array() : (array) $item->classes;
            $classes[] = \'menu-item-\' . $item->ID;
            $class_names = join( \' \', apply_filters( \'nav_menu_css_class\', array_filter( $classes ), $item, $args ) );
            if ( $args->has_children )
                $class_names .= \' cd-library\';
            if ( in_array( \'current-menu-item\', $classes ) )
                $class_names .= \' active\';
            $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 . $value . $class_names .\'>\';
            $atts = array();
            $atts[\'title\']  = ! empty( $item->title )   ? $item->title  : \'\';
            $atts[\'target\'] = ! empty( $item->target )  ? $item->target : \'\';
            $atts[\'rel\']    = ! empty( $item->xfn )     ? $item->xfn    : \'\';
            // If item has_children add atts to a.
            if ( $args->has_children && $depth === 0 ) {
                $atts[\'href\']           = \'#\';
                $atts[\'data-toggle\']    = \'dropdown\';
                $atts[\'class\']          = \'dropdown-toggle\';
                $atts[\'aria-haspopup\']  = \'true\';
            } else {
                $atts[\'href\'] = ! empty( $item->url ) ? $item->url : \'\';
            }
            $atts = apply_filters( \'nav_menu_link_attributes\', $atts, $item, $args );
            $attributes = \'\';
            foreach ( $atts as $attr => $value ) {
                if ( ! empty( $value ) ) {
                    $value = ( \'href\' === $attr ) ? esc_url( $value ) : esc_attr( $value );
                    $attributes .= \' \' . $attr . \'="\' . $value . \'"\';
                }
            }
            $item_output = $args->before;
            /*
             * Glyphicons
             * ===========
             * Since the the menu item is NOT a Divider or Header we check the see
             * if there is a value in the attr_title property. If the attr_title
             * property is NOT null we apply it as the class name for the glyphicon.
             */
            if ( ! empty( $item->attr_title ) )
                $item_output .= \'<a\'. $attributes .\'><span class="glyphicon \' . esc_attr( $item->attr_title ) . \'"></span>&nbsp;\';
            else
                $item_output .= \'<a\'. $attributes .\'>\';
            $item_output .= $args->link_before . apply_filters( \'the_title\', $item->title, $item->ID ) . $args->link_after;
            $item_output .= ( $args->has_children && 0 === $depth ) ? \' <span class="caret"></span></a>\' : \'</a>\';
            $item_output .= $args->after;
            $output .= apply_filters( \'walker_nav_menu_start_el\', $item_output, $item, $depth, $args );
        }
    }
    /**
     * Traverse elements to create list from elements.
     *
     * Display one element if the element doesn\'t have any children otherwise,
     * display the element and its children. Will only traverse up to the max
     * depth and no ignore elements under that depth.
     *
     * This method shouldn\'t be called directly, use the walk() method instead.
     *
     * @see Walker::start_el()
     * @since 2.5.0
     *
     * @param object $element Data object
     * @param array $children_elements List of elements to continue traversing.
     * @param int $max_depth Max depth to traverse.
     * @param int $depth Depth of current element.
     * @param array $args
     * @param string $output Passed by reference. Used to append additional content.
     * @return null Null on failure with no changes to parameters.
     */
    public function display_element( $element, &$children_elements, $max_depth, $depth, $args, &$output ) {
        if ( ! $element )
            return;
        $id_field = $this->db_fields[\'id\'];
        // Display this element.
        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 );
    }
    /**
     * Menu Fallback
     * =============
     * If this function is assigned to the wp_nav_menu\'s fallback_cb variable
     * and a manu has not been assigned to the theme location in the WordPress
     * menu manager the function with display nothing to a non-logged in user,
     * and will add a link to the WordPress menu manager if logged in as an admin.
     *
     * @param array $args passed from the wp_nav_menu function.
     *
     */
    public static function fallback( $args ) {
        if ( current_user_can( \'manage_options\' ) ) {
            extract( $args );
            $fb_output = null;
            if ( $container ) {
                $fb_output = \'<\' . $container;
                if ( $container_id )
                    $fb_output .= \' id="\' . $container_id . \'"\';
                if ( $container_class )
                    $fb_output .= \' class="\' . $container_class . \'"\';
                $fb_output .= \'>\';
            }
            $fb_output .= \'<ul\';
            if ( $menu_id )
                $fb_output .= \' id="\' . $menu_id . \'"\';
            if ( $menu_class )
                $fb_output .= \' class="\' . $menu_class . \'"\';
            $fb_output .= \'>\';
            $fb_output .= \'<li><a href="\' . admin_url( \'nav-menus.php\' ) . \'">Add a menu</a></li>\';
            $fb_output .= \'</ul>\';
            if ( $container )
                $fb_output .= \'</\' . $container . \'>\';
            echo $fb_output;
        }
    }
}

//Use theme
 <?php wp_nav_menu( array(
                \'menu\'              => \'main-nav\',
                \'theme_location\'    => \'main-nav\',
                \'depth\'             => 2,
                \'container\'         => false,
                \'menu_class\'        => \'main-navigation\',
                \'fallback_cb\'       => \'wp_bootstrap_navwalker::fallback\',
                \'walker\'            => new wp_bootstrap_navwalker())
            ); ?>

<?php

/**
 * Bootstrap NavWalker
 * Class Name: Bootstrap_NavWalker
 * Author: Bishal Napit
 * Author URI: https://napitwptech.com/
 * GitHub URI: https://github.com/mebishalnapit/bootstrap-navwalker/
 * Description: A custom WordPress nav walker class to implement the Bootstrap 4 navigation style in a custom WordPress
 * Bootstrap based theme using the WordPress built in menu manager.
 * License: GNU General Public License v3 or later
 * License URI: http://www.gnu.org/licenses/gpl-3.0.html
 */
class Bootstrap_NavWalker extends Walker_Nav_Menu {

    // Create the $current_menu_id_bootstrap variable for generating the current menu id
    protected $current_menu_id_bootstrap;

    /**
     * Starts the list before the elements are added.
     *
     * @since 3.0.0
     * @see   Walker::start_lvl()
     *
     * @param string   $output Passed by reference. Used to append additional content.
     * @param int      $depth  Depth of menu item. Used for padding.
     * @param stdClass $args   An object of wp_nav_menu() arguments.
     */
    public function start_lvl( &$output, $depth = 0, $args = array() ) {
        // Use the current menu id generated via start_el()
        $current_menu_id = $this->current_menu_id_bootstrap;

        // Assign the dynamic id for use inside the dropdown menu, ie, sub-menu for Bootstrap
        $id = \'aria-labelledby="navbar-dropdown-menu-link-\' . $current_menu_id->ID . \'"\';

        if ( isset( $args->item_spacing ) && \'discard\' === $args->item_spacing ) {
            $t = \'\';
            $n = \'\';
        } else {
            $t = "\\t";
            $n = "\\n";
        }

        $indent = str_repeat( $t, $depth );

        /**
         * Add the classes for the dropdown menu in WordPress
         *
         * 1. For WordPress default: \'.sub-menu\'
         * 2. For Bootstrap Sub-Menu: \'.dropdown-menu\'
         */
        $classes = array( \'sub-menu\', \'dropdown-menu\' );

        /**
         * Filters the CSS class(es) applied to a menu list element.
         *
         * @since 4.8.0
         *
         * @param array    $classes The CSS classes that are applied to the menu `<ul>` element.
         * @param stdClass $args    An object of `wp_nav_menu()` arguments.
         * @param int      $depth   Depth of menu item. Used for padding.
         */
        $class_names = join( \' \', apply_filters( \'nav_menu_submenu_css_class\', $classes, $args, $depth ) );
        $class_names = $class_names ? \' class="\' . esc_attr( $class_names ) . \'"\' : \'\';

        /**
         * Change <ul> to <div> for Bootstrap Navigation
         * Add the current menu id for the sub-menu toggle feature for Bootstrap
         */
        $output .= "{$n}{$indent}<div $class_names $id>{$n}";
    }

    /**
     * Ends the list of after the elements are added.
     *
     * @since 3.0.0
     * @see   Walker::end_lvl()
     *
     * @param string   $output Passed by reference. Used to append additional content.
     * @param int      $depth  Depth of menu item. Used for padding.
     * @param stdClass $args   An object of wp_nav_menu() arguments.
     */
    public function end_lvl( &$output, $depth = 0, $args = array() ) {
        if ( isset( $args->item_spacing ) && \'discard\' === $args->item_spacing ) {
            $t = \'\';
            $n = \'\';
        } else {
            $t = "\\t";
            $n = "\\n";
        }

        $indent = str_repeat( $t, $depth );

        /**
         * Change </ul> to </div> for Bootstrap Navigation
         */
        $output .= "$indent</div>{$n}";
    }

    /**
     * Starts the element output.
     *
     * @since 3.0.0
     * @since 4.4.0 The {@see \'nav_menu_item_args\'} filter was added.
     * @see   Walker::start_el()
     *
     * @param string   $output Passed by reference. Used to append additional content.
     * @param WP_Post  $item   Menu item data object.
     * @param int      $depth  Depth of menu item. Used for padding.
     * @param stdClass $args   An object of wp_nav_menu() arguments.
     * @param int      $id     Current item ID.
     */
    public function start_el( &$output, $item, $depth = 0, $args = array(), $id = 0 ) {
        // Find the current menu item id to be used for start_lvl()
        $this->current_menu_id_bootstrap = $item;

        if ( isset( $args->item_spacing ) && \'discard\' === $args->item_spacing ) {
            $t = \'\';
            $n = \'\';
        } else {
            $t = "\\t";
            $n = "\\n";
        }

        $indent = ( $depth ) ? str_repeat( $t, $depth ) : \'\';

        $classes   = empty( $item->classes ) ? array() : ( array ) $item->classes;
        $classes[] = \'menu-item-\' . $item->ID;

        /**
         * Add class \'.nav-item\' inside <li> tag for Bootstrap
         */
        $classes[] = \'nav-item\';

        /**
         * Add class \'.active\' inside <li> tag for Bootstrap active menu as well as for the parent menu, which have the active sub-menu
         */
        if ( in_array( \'current-menu-item\', $classes ) || in_array( \'current-menu-parent\', $classes ) ) {
            $classes[] = \'active\';
        }

        /**
         * Add class \'.dropdown\' inside <li> tag for Bootstrap dropdown menu, ie, <li> having sub-menu
         */
        if ( in_array( \'menu-item-has-children\', $classes ) ) {
            $classes[] = \'dropdown\';
        }

        /**
         * Filters the arguments for a single nav menu item.
         *
         * @since 4.4.0
         *
         * @param stdClass $args  An object of wp_nav_menu() arguments.
         * @param WP_Post  $item  Menu item data object.
         * @param int      $depth Depth of menu item. Used for padding.
         */
        $args = apply_filters( \'nav_menu_item_args\', $args, $item, $depth );

        /**
         * Filters the CSS class(es) applied to a menu item\'s list item element.
         *
         * @since 3.0.0
         * @since 4.1.0 The `$depth` parameter was added.
         *
         * @param array    $classes The CSS classes that are applied to the menu item\'s `<li>` element.
         * @param WP_Post  $item    The current menu item.
         * @param stdClass $args    An object of wp_nav_menu() arguments.
         * @param int      $depth   Depth of menu item. Used for padding.
         */
        $class_names = join( \' \', apply_filters( \'nav_menu_css_class\', array_filter( $classes ), $item, $args, $depth ) );
        $class_names = $class_names ? \' class="\' . esc_attr( $class_names ) . \'"\' : \'\';

        /**
         * Filters the ID applied to a menu item\'s list item element.
         *
         * @since 3.0.1
         * @since 4.1.0 The `$depth` parameter was added.
         *
         * @param string   $menu_id The ID that is applied to the menu item\'s `<li>` element.
         * @param WP_Post  $item    The current menu item.
         * @param stdClass $args    An object of wp_nav_menu() arguments.
         * @param int      $depth   Depth of menu item. Used for padding.
         */
        $id = apply_filters( \'nav_menu_item_id\', \'menu-item-\' . $item->ID, $item, $args, $depth );
        $id = $id ? \' id="\' . esc_attr( $id ) . \'"\' : \'\';

        /**
         * <li> is required for parent menu only in Bootstrap
         */
        if ( $depth === 0 ) {
            $output .= $indent . \'<li\' . $id . $class_names . \'>\';
        }

        $atts           = array();
        $atts[\'title\']  = ! empty( $item->attr_title ) ? $item->attr_title : \'\';
        $atts[\'target\'] = ! empty( $item->target ) ? $item->target : \'\';
        $atts[\'rel\']    = ! empty( $item->xfn ) ? $item->xfn : \'\';
        $atts[\'href\']   = ! empty( $item->url ) ? $item->url : \'\';

        /**
         * Add \'.nav-link\' class for <a> in parent menu for Bootstrap
         */
        if ( $depth === 0 ) {
            $atts[\'class\'] = \'nav-link\';
        }

        /**
         * Add the attributes for <a> in parent menu
         *
         * 1. Add \'.dropdown-toggle\' class for <a> in parent menu if it has sub-menu as required for Bootstrap
         * 2. Add \'.dropdown\' as \'data-toggle\' attribute in <a> in parent menu if it has sub-menu as required for Bootstrap
         * 3. Add the current menu id attribute to indicate the exact menu to toggle for set in sub-menu div
         * 4. Add the attribute of \'true\' for \'aria-haspopup\' in parent menu to indicate it has sub-menus
         * 5. Add the attribute of \'false\' for \'aria-expanded\' in parent menu to indicate the sub-menus is hidden by default
         * 6. Add the \'#\' link in the <a> tag in the parent menu if it has sub-menu as required for Bootstrap
         */
        if ( $depth === 0 && in_array( \'menu-item-has-children\', $classes ) ) {
            $atts[\'class\']         .= \' dropdown-toggle\';
            $atts[\'data-toggle\']   = \'dropdown\';
            $atts[\'id\']            = \'navbar-dropdown-menu-link-\' . $item->ID;
            $atts[\'aria-haspopup\'] = "true";
            $atts[\'aria-expanded\'] = "false";
            $atts[\'href\']          = \'#\';
        }

        /**
         * Add the attributes for <a> in sub-menu
         * 1. Add \'.dropdown-item\' class for <a> inside sub-menu for Bootstrap
         * 2. Add the current menu id attribute if you want to style the menu differently
         */
        if ( $depth > 0 ) {
            $atts[\'class\'] = \'dropdown-item\';
            $atts[\'id\']    = \'menu-item-\' . $item->ID;
        }

        /**
         * Add \'.active\' class inside <a> in sub-menu for Bootstrap
         */
        if ( in_array( \'current-menu-item\', $item->classes ) ) {
            $atts[\'class\'] .= \' active\';
        }

        /**
         * Add \'.disabled\' class for <a> in menu for Bootstrap disabled class
         */
        if ( in_array( \'disabled\', $item->classes ) ) {
            $atts[\'class\'] .= \' disabled\';
        }

        /**
         * Filters the HTML attributes applied to a menu item\'s anchor element.
         *
         * @since                  3.6.0
         * @since                  4.1.0 The `$depth` parameter was added.
         *
         * @param array    $atts   {
         *                         The HTML attributes applied to the menu item\'s `<a>` element, empty strings are ignored.
         *
         * @type string    $title  Title attribute.
         * @type string    $target Target attribute.
         * @type string    $rel    The rel attribute.
         * @type string    $href   The href attribute.
         *                         }
         *
         * @param WP_Post  $item   The current menu item.
         * @param stdClass $args   An object of wp_nav_menu() arguments.
         * @param int      $depth  Depth of menu item. Used for padding.
         */
        $atts = apply_filters( \'nav_menu_link_attributes\', $atts, $item, $args, $depth );

        $attributes = \'\';
        foreach ( $atts as $attr => $value ) {
            if ( ! empty( $value ) ) {
                $value = ( \'href\' === $attr ) ? esc_url( $value ) : esc_attr( $value );

                /**
                 * If \'.disabled\' class is added to the menu, add the url of \'#\' in it
                 */
                if ( in_array( \'disabled\', $item->classes ) ) {
                    $value = ( \'href\' === $attr ) ? esc_url( \'#\' ) : esc_attr( $value );
                }

                $attributes .= \' \' . $attr . \'="\' . $value . \'"\';
            }
        }

        /** This filter is documented in wp-includes/post-template.php */
        $title = apply_filters( \'the_title\', $item->title, $item->ID );

        /**
         * Filters a menu item\'s title.
         *
         * @since 4.4.0
         *
         * @param string   $title The menu item\'s title.
         * @param WP_Post  $item  The current menu item.
         * @param stdClass $args  An object of wp_nav_menu() arguments.
         * @param int      $depth Depth of menu item. Used for padding.
         */
        $title = apply_filters( \'nav_menu_item_title\', $title, $item, $args, $depth );

        $item_output = $args->before;
        $item_output .= \'<a\' . $attributes . \'>\';
        $item_output .= $args->link_before . $title . $args->link_after;
        $item_output .= \'</a>\';
        $item_output .= $args->after;

        /**
         * Filters a menu item\'s starting output.
         * The menu item\'s starting output only includes `$args->before`, the opening `<a>`,
         * the menu item\'s title, the closing `</a>`, and `$args->after`. Currently, there is
         * no filter for modifying the opening and closing `<li>` for a menu item.
         *
         * @since 3.0.0
         *
         * @param string   $item_output The menu item\'s starting HTML output.
         * @param WP_Post  $item        Menu item data object.
         * @param int      $depth       Depth of menu item. Used for padding.
         * @param stdClass $args        An object of wp_nav_menu() arguments.
         */
        $output .= apply_filters( \'walker_nav_menu_start_el\', $item_output, $item, $depth, $args );
    }

    /**
     * Ends the element output, if needed.
     *
     * @since 3.0.0
     * @see   Walker::end_el()
     *
     * @param string   $output Passed by reference. Used to append additional content.
     * @param WP_Post  $item   Page data object. Not used.
     * @param int      $depth  Depth of page. Not Used.
     * @param stdClass $args   An object of wp_nav_menu() arguments.
     */
    public function end_el( &$output, $item, $depth = 0, $args = array() ) {
        if ( isset( $args->item_spacing ) && \'discard\' === $args->item_spacing ) {
            $t = \'\';
            $n = \'\';
        } else {
            $t = "\\t";
            $n = "\\n";
        }

        /**
         * <li> is required for parent menu only in Bootstrap
         */
        if ( $depth === 0 ) {
            $output .= "</li>{$n}";
        }
    }

    /**
     * Fallback menu
     * If you assign the fallback menu for your custom menu setup via wp_nav_menu function, then, this function will be
     * rendered if no menu is assigned to that menu location. You need to assign it via \'fallback_cb\' array. Also, this
     * will be only rendered to the logged in users pointing them to the menu manager url.
     *
     * @param $args Arrays passed from the wp_nav_menu function
     */
    public static function fallback( $args ) {
        if ( current_user_can( \'edit_theme_options\' ) ) {
            $container       = $args[\'container\'];
            $container_id    = $args[\'container_id\'];
            $container_class = $args[\'container_class\'];
            $menu_class      = $args[\'menu_class\'];
            $menu_id         = $args[\'menu_id\'];

            // If there is container render it
            if ( $container ) {
                echo \'<\' . esc_attr( $container );

                // If container id is set render it
                if ( $container_id ) {
                    echo \' id="\' . esc_attr( $container_id ) . \'"\';
                }

                // If container class is set render it
                if ( $container_class ) {
                    echo \' class="\' . esc_attr( $container_class ) . \'"\';
                }

                echo \'>\';
            }

            // Default wrapper for menu is <ul>
            echo \'<ul\';

            // If menu id has been set render it
            if ( $menu_id ) {
                echo \' id="\' . esc_attr( $menu_id ) . \'"\';
            }

            // If menu class has been set render it
            if ( $menu_class ) {
                echo \' class="\' . esc_attr( $menu_class ) . \'"\';
            }

            // Close <ul> div wrapper for menu
            echo \'>\';

            // Display the link to Add New Menu
            echo \'<li class="nav-item active"><a class="nav-link" href="\' . esc_url( admin_url( \'nav-menus.php\' ) ) . \'">\';
            esc_html_e( \'Add a menu\', \'theme-textdomain\' );
            echo \'</a></li>\';

            // Close the main <ul>
            echo \'</ul>\';

            // Close the main container div
            if ( $container ) {
                echo \'</\' . esc_attr( $container ) . \'>\';
            }

        }
    }

}