我正在使用wp_nav_menu 对于我只想在有子菜单项要显示时显示的子菜单（包括周围的html）。

问题是，函数总是返回菜单项（应该返回时），或者返回空列表（没有显示时）。我需要它（并且认为它会）返回false。

这是我的密码。

// Capture submenu as a variable
$args = array( 
            \'theme_location\' => $in_menu,
            \'echo\'           => \'0\',
            \'sub_menu\'       => true,
            \'fallback_cb\'    => \'coepio_return_false\'
    ); // Note I\'ve also tried \'fallback_cb\' => false with the same result
$submenu = wp_nav_menu( $args );

// If the menu exists
if( $submenu ) {
    ?>
    <div id="submenu" class="sidebar cf" role="navigation">

        <div class="widget">
            <div id="submenu-title" class="widget-title">
                <h4>In This Section</h4>
            </div>
            <div class="widget-content">
                <?php 
                echo $submenu;
                ?>
            </div>
        </div>

    </div><!-- #submenu -->
    <?php
}

// Submenus - required for the submenu (above) to work
// filter_hook function to react on sub_menu flag
function coepio_submenu( $sorted_menu_items, $args ) {
  if ( isset( $args->sub_menu ) ) {
    $root_id = 0;

    // find the current menu item
    foreach ( $sorted_menu_items as $menu_item ) {
      if ( $menu_item->current ) {
        // set the root id based on whether the current menu item has a parent or not
        $root_id = ( $menu_item->menu_item_parent ) ? $menu_item->menu_item_parent : $menu_item->ID;
        break;
      }
    }

    $menu_item_parents = array();
    foreach ( $sorted_menu_items as $key => $item ) {
      // init menu_item_parents
      if ( $item->ID == $root_id ) $menu_item_parents[] = $item->ID;

      if ( in_array( $item->menu_item_parent, $menu_item_parents ) ) {
        // part of sub-tree: keep!
        $menu_item_parents[] = $item->ID;
      } else {
        // not part of sub-tree: away with it!
        unset( $sorted_menu_items[$key] );
      }
    }

    return $sorted_menu_items;
  } else {
    return $sorted_menu_items;
  }
}
add_filter( \'wp_nav_menu_objects\', \'coepio_submenu\', 10, 2 );