The wp_list_pages() function displays a list of WordPress pages as links and is often used to display navigation menus. When it prints the list of links, it adds a CSS class current_page_item to the list item tag of the current page. This allows custom styling to be applied to the link e.g. to highlight a link to indicate the page that the visitor is on.

The limitation with this is that it only works if you are viewing a page or an attachment, or are on the posts page (as set in Settings > Reading).

I was working on an archive page for a custom taxonomy and wanted to have the current_page_item CSS class added to the list item of a particular link of my choice. After poking around a bit in the wp_list_pages() code listing, I discovered it’s possible to hack the $wp_query object to make wp_list_pages() do what I wanted it to.

Here’s how:

// Get the ID of the link you want highlighted. Either:
// - hardcode it (as below)
// - or query the database to get it
$the_id = "1";

// Make a copy of the $wp_query object
$temp_query = clone $wp_query;

// Trick WordPress into thinking we're on a page with ID $the_id
$wp_query->is_page = 1;
$wp_query->queried_object_id = $the_id;

// Display pages
wp_list_pages("title_li=");

// Reset $wp_query
$wp_query = clone $temp_query;

Notes:

• $wp_query->is_page needs to be set to 1 (true) because wp_list_pages() does not set a current page unless is_page() or is_attachment() or $wp_query->is_posts_page returns true.
• If you only want this code to run when you are on certain page you can wrap it in an if statement that checks a WordPress conditional tag. In my case I only wanted to run this code when a taxonomy archive was being displayed so I used is_tax().
• See http://www.jenst.se/2008/03/17/wordpress-get-id-by-post-or-page-name/ on how to query the database by post/page name to get an ID.