Layer Navigation Function

For a project I needed to have separate layers of navigation on different parts in my template. Problem was that I didn’t want to have just the child pages of the current page, i needed a particular layer of navigation from the specific ‘branch’ of the current page.

I came up with the following function:

// Returns a specfic layer of the navigation relative to the root
// and based on the 'branch' of the current page.
// $layer is 1, would be the first layer of SUBNAVIGATION

if ( !function_exists( 'get_ancestor_id' ) ) {
    function get_ancestor_id( $current_page_id, $layer ){

        $ancestors_arr = get_post_ancestors( $current_page_id );
        $ancestors_arr = array_reverse ($ancestors_arr);
        $ancestors_depth = count($ancestors_arr);

        if( $layer > 0 && $layer > $ancestors_depth ) {
        // The current page less deep dan de specified layer. 

            if( $ancestors_depth - $layer == -1 ){
                  $menuroot_pageid = $current_page_id;
            } else {
                return false;
            }

        } else if ( $layer < 0 ) {

            // Set ancestor PageID relative to current page
            // e.g. -2 sets grandparent as menuroot_pageid;
            $index = $ancestors_depth + $layer; // results in something like 2 + (-1) which gets parents
            $menuroot_pageid = $ancestors_arr[ $index ];

        } else {

            // Set ancestor PageID relative to root
            $menuroot_pageid = $ancestors_arr[ $layer - 1]; // -1 is correction

        }

        return $menuroot_pageid;

    }
}

if ( !function_exists( 'has_children' ) ) {
    function has_children($post_id) {
        $children = get_pages("child_of=$post_id");
        if( count( $children ) != 0 ) {
return true; }
        else { return false; }
    }
}

In the theme you can acces a specific layer of navigation through:

<?php if ( $rootID = get_ancestor_id( $page_id, 1 ) ) : ?>
		<?php if ( has_children( $rootID ) ) : ?>
				<nav>
					<ul>
					<?php echo wp_list_pages("title_li=&child_of=". $rootID ."&echo=0&depth=1&sort_column=menu_order"); ?>
					</ul>
				</nav><
		<?php endif; ?>
	<?php endif; ?>

I’d like to share this code with you, maybe it’s useful for someone. Besides that I’d like to know if anyone has any comments; and things by which I can improve.

Kind regards.