As a company that does both Drupal and WordPress websites, it can be frustrating sometimes when functions that are so easy for one platform are so difficult to duplicate on the other. One example is the Menu Block functionality that will create a submenu relative to whatever page you’re on. Like many things in WordPress, it often boils down to pasting a snippet of code in your template file.
The key is the feature is leveraging WordPress’s wp_list_pages function and grabbing the current page’s parent ID.
Paste this snippet into your theme’s sidebar template file (or anywhere else you want it to show up).
<div id="subnav">
<?php
$ancestor_id = $post->post_parent;
$ancestors = get_ancestors($post->ID, 'page');
if(isset($ancestors[1])) {
$ancestor_id = $ancestors[1];
}
$descendants = get_pages(array('child_of' => $ancestor_id));
$incl = "";
foreach ($descendants as $page) {
if (($page->post_parent == $ancestor_id) ||
($page->post_parent == $post->post_parent) ||
($page->post_parent == $post->ID))
{
$incl .= $page->ID . ",";
}
}
?>
<ul>
<?php wp_list_pages(array("child_of" => $ancestor_id, "include" => $incl, "link_before" => "", "title_li" => "", "sort_column" => "menu_order"));?>
</ul>
</div>
This code will sort the pages by on the page order, so make sure you assign unique values for each or you’ll get unexpected sorting results.