Outputting main menu in full in page.tpl.php

Question

I'm using the code below to print my main menu in page.tpl.php:

<?php
$main_menu = menu_navigation_links('main-menu');
print theme('links', array(
'links' => $main_menu,
'attributes' => array(
'id' => 'main-menu',
'class' => array('links', 'clearfix'),
),

'heading' => array(
'text' => t('Main menu'),
'level' => 'h2',
'class' => array('element-invisible'),
),
));
?>

However, it is only outputting the top-level menus of my navigation. Is there a piece of code I can add that will output submenus too?

Answer 1

Calling menu_navigation_links() with only the menu name by default provides only the top level links. To delve deeper you need to provide the second $level argument, eg:

$main_menu =menu_navigation_links('main-menu', 1);

will provide the top and next level links, and:

$main_menu =menu_navigation_links('main-menu', 2);

will provide one level deeper.