walker类是一个抽象类，旨在帮助遍历和显示具有层次（或树状）结构的元素。它实际上并不“做”（在生成HTML的意义上）任何事情。

在模板文件中，我们将使用wp\\u nav\\u menu（）函数两次，指向相同的主题位置（我将其称为“primary”）。如果您还没有注册主题位置，那么应该阅读本文。无论使用哪个主题位置，都应该将菜单保存到该位置。我们将显示此菜单两次。首先，无论您想在哪里显示“顶级”菜单：

wp_nav_menu( array(\'theme_location\'=>\'primary\',\'depth\' => 1) );

wp_nav_menu( array(\'theme_location\'=>\'primary\',\'walker\' => new SH_Child_Only_Walker(),\'depth\' => 0) );

class SH_Child_Only_Walker extends Walker_Nav_Menu {

    // Don\'t start the top level
    function start_lvl(&$output, $depth=0, $args=array()) {
        if( 0 == $depth )
            return;
        parent::start_lvl(&$output, $depth,$args);
    }

    // Don\'t end the top level
    function end_lvl(&$output, $depth=0, $args=array()) {
        if( 0 == $depth )
            return;
        parent::end_lvl(&$output, $depth,$args);
    }

    // Don\'t print top-level elements
    function start_el(&$output, $item, $depth=0, $args=array()) {
        if( 0 == $depth )
            return;
        parent::start_el(&$output, $item, $depth, $args);
    }

    function end_el(&$output, $item, $depth=0, $args=array()) {
        if( 0 == $depth )
            return;
        parent::end_el(&$output, $item, $depth, $args);
    }

    // Only follow down one branch
    function display_element( $element, &$children_elements, $max_depth, $depth=0, $args, &$output ) {

        // Check if element as a \'current element\' class
        $current_element_markers = array( \'current-menu-item\', \'current-menu-parent\', \'current-menu-ancestor\' );
        $current_class = array_intersect( $current_element_markers, $element->classes );

        // If element has a \'current\' class, it is an ancestor of the current element
        $ancestor_of_current = !empty($current_class);

        // If this is a top-level link and not the current, or ancestor of the current menu item - stop here.
        if ( 0 == $depth && !$ancestor_of_current)
            return

        parent::display_element( $element, &$children_elements, $max_depth, $depth, $args, &$output );
    }
}