Wordpress Subnavigation aus Navigationen (wp_nav_menu())

wordpress_subnav.php

<ul id="subnavigation">
<?php
	function my_nav_submenu_objects( $items, $args ) {
		$subnav_elements = array();
		// Sammle alle Subnavielemente
		foreach ($items as $key => $value) {
			if($value->menu_item_parent != 0){
				$subnav_elements[$key]=$value;
			}
		}
		// Vergleiche menu_item_parent mit selektiertem Element
		foreach ($items as $key => $value) {
			if($value->current)
			{
				if($value->menu_item_parent != 0)
				{
					$searchID = $value->menu_item_parent;
				}
				else
				{
					$searchID = $value->db_id;
				}
				foreach ($subnav_elements as $keyy => $valuee) {
					if($valuee->menu_item_parent != $searchID)
					{
						unset($subnav_elements[$keyy]);
					}
				}
			}
		}
		return $subnav_elements;
	}
	add_filter( 'wp_nav_menu_objects', 'my_nav_submenu_objects', 0, 2 );

	$defaults = array(
		'container' => '',
		'menu'            => 'Hauptnavigation',
		'items_wrap'      => '%3$s',
		'depth'           => 2
	); 
?>

<?php 
	wp_nav_menu( $defaults ); 
	remove_filter( 'wp_nav_menu_objects', 'my_nav_submenu_objects',0,2);
?>
</ul>