Tag: wp_nav_menu

functions.php

// filter menu to submenu
add_filter( 'wp_nav_menu_objects', 'submenu_limit', 10, 2 );
function submenu_limit( $items, $args ) {
	if ( empty( $args->page_parent ) ) {
		return $items;
	}
	$subitems = array();
	foreach ($items as $key => $item) {
		if($item->post_parent == $args->page_parent){
			$subitems[] = $item;
		}
	}
	foreach ($subitems as $key => $subitem) {
		submenu_get_children($items, $subitems, $subitem);
	}
	return $subitems;
}
function submenu_get_children($items, &$subitems, $subitem){
	foreach ($items as $key => $item) {
		if($subitem->ID == $item->menu_item_parent){
			$subitems[] = $item;
			submenu_get_children($items, $subitems, $item);
		}
	}
}

Usage in template

$parents = get_post_ancestors( $post->ID );
$parent_id = ($parents) ? $parents[count($parents)-1]: $post->ID;
$args = array(
    'post_parent' => $parent_id,
);
$children = get_children( $args );

// optional, check if page has children
if($children){
	wp_nav_menu([
		'menu'            => 'menu-1',
		'theme_location'  => 'menu-1',
		'container'       => '',
		'container_id'    => '',
		'container_class' => '',
		'menu_id'         => false,
		'menu_class'      => 'navbar-nav',
		'depth'           => 3,
		'page_parent'	  => $parent_id
	]);
}