class=”parent” for wp_list_pages?

Phew! Bit more complex than I would’ve liked – if only the filter page_css_class passed back $args it would save a lot of effort (may submit this to trac).

Since 3.3 it’s as easy as this!

function add_parent_class( $css_class, $page, $depth, $args )
{
    if ( ! empty( $args['has_children'] ) )
        $css_class[] = 'parent';
    return $css_class;
}
add_filter( 'page_css_class', 'add_parent_class', 10, 4 );

For those on pre WordPress 3.3, here’s the workhorse:

/**
 * Extend the default page walker class to append class names for pages that
 * are parents.
 * @uses Walker_Page
 */ 
class My_Page_Walker extends Walker_Page
{
    /**
     * Filter in the classes for parents.
     */
    function _filterClass( $class )
    {
        $class[] = 'parent'; // change this to whatever classe(s) you require
        return $class;
    }

    /**
     * This is effectively a wrapper for the default method, dynamically adding
     * and removing the class filter when the current item has children.
     */
    function start_el( &$output, $page, $depth, $args, $current_page )
    {
        if ( !empty($args['has_children']) )
            add_filter( 'page_css_class', array( &$this, '_filterClass') );

        parent::start_el( $output, $page, $depth, $args, $current_page );

        if ( !empty($args['has_children']) )
            remove_filter( 'page_css_class', array( &$this, '_filterClass') );
    }
}

I’d advise placing the class in your functions.php, then it’s available wherever you’d like to use it.

To use it, call wp_list_pages() like so;

// You need to pass the walker argument to wp_list_pages(). You must use an
// array to do this.
wp_list_pages(array(
    'walker'   => new My_Page_Walker,
    'title_li' => ''
));