Display all submenus

Question

For a custom jquery menu I'd like to show all submenus and hide / show each on demand. However my problem is to show all submenus in the first place.

As of now I am managing the first level through the admin menu section: adding menu items to primary menu. Display works like so:

wp_nav_menu(
   array (
        'sort_column' => 'menu_order'
        , 'container' => 'ul'
        , 'menu_id' => 'main-nav'
        , 'theme_location' => 'primary-menu'
        , 'depth' => 1
   )
);

The second level is (unfortunately) managed through the pages section with post_parent and menu_order. Therefore displaying it works like so:

global $post;
$has_post_parent = $post && $post->post_parent;
$post_id = $post ? $post->ID : -1;
$top = $has_post_parent ? array_pop( get_post_ancestors($post_id) ) : $post_id;
echo '<div id="submenu" class="clearfix"><ul>';
wp_list_pages(
    array(
        'child_of' => $top
        , 'depth' => 1
        , 'title_li' => ''
    )
);
echo '</ul></div>';

I already tried to loop through the main menu items (first-level) like the following, but that left me with empty submenus, even though the main items seemed correct at first glance:

$locations = get_nav_menu_locations();
$menu = wp_get_nav_menu_object($locations['primary-menu']);
$menu_items = wp_get_nav_menu_items($menu->term_id);
foreach($menu_items as $menu_item) {
    $current_id = $menu_item->ID;
    $is_current_class = ($current_id == $top) ? 'current-submenu' : '';

    echo "<ul class='$is_current_class' data-parent='$current_id'>";
    wp_list_pages(
        array(
            'child_of' => $current_id
            , 'depth' => 1
            , 'echo' => 1
            , 'title_li' => ''
        )
    );
    echo '</ul>';
}

EDIT

Even though I have fixed my initial solution, I am still very interested in a solution, where the menu can be completely managed through the wp-admin menus section.

Answer 1

Ok, the problem in my solution was the use of $menu_item->ID instead of
$menu_item->object_id. So the full correct logic is like so:

function print_sub_menus() {
    global $post;

    // get current page
    $post_id = $post ? $post->ID : -1;
    $has_post_parent = $post && $post->post_parent;
    $top = $has_post_parent ? array_pop( get_post_ancestors($post_id) ) : $post_id;

    // get all main menu items
    $locations = get_nav_menu_locations();
    $menu = wp_get_nav_menu_object($locations['primary-menu']);
    $menu_items = wp_get_nav_menu_items($menu->term_id);

    echo '<div id="submenu" class="clearfix">';
    foreach($menu_items as $menu_item) {
        $current_id = $menu_item->object_id;
        $is_current_class = ($current_id == $top) ? 'current-submenu' : '';

        echo "<ul class='$is_current_class' data-parent='$current_id'>";
        wp_list_pages(
            array(
                'child_of' => $current_id
                , 'depth' => 1
                , 'echo' => 1
                , 'title_li' => ''
            )
        );
        echo '</ul>';
    }
    echo '</div>';
}