how to display part of a menu tree?

I'm trying to deal with Wordpress 3.0. It's rather cool thing but I can't get on with one problem. For example, I have such menu tree. Menu tree is constructed from pages.

Home
   news
   video
   audio
Blog
   About author
   Favourite colors
      red
      blue
      green
My car
   wheels
   tires

The Idea is: main menu consists of root elements: home, blog, my car On the left side I would like to display children elements of current active root element.

For exammple if person is on the "home" page, on the left part he should see:

  news
  video
  audio

If user is on the "Blog" page, he should see:

About author
       Favourite colors
          red
          blue
          green

I can't find an API to do that. Can you sugest me please where can I find it?

UPD: @Jason McCreary I've seen I've seen wp_list_pages() and tried it. I din't get how can I use it: Please, see my template for a page:

    <?php
/*
 Template Name: page_news

 * @package WordPress
 * @subpackage Twenty_Ten
 * @since Twenty Ten 1.0
 */

get_header(); ?>
<h1>page_news</h1>
<h1>Children menu:</h1>
<?php wp_list_pages('echo=0&child_of=8&title_li='); ?>
<div id="container">
        <div id="content" role="main">

        <?php
        /** Get category id by name*/
        //$catId = get_category_by_slug('news')->term_id;
        query_posts('category_name=news');
        get_template_part( 'loop', 'page' );
        ?>

        </div><!-- #content -->
</div><!-- #container -->

<?php get_sidebar(); ?>
<?php get_footer(); ?>

See this line of code:

<?php wp_list_pages('echo=0&child_of=8&title_li='); ?>

I do have the page with id=8 (I see it in URL). Page with id=8 has several children. I want to print them, but they are not printed. The output of the function wp_list_pages() is nothing. I don't know why... :(

You can write a filter_hook to accomplish this.

My method: create an additional start_in argument for wp_nav_menu using my custom hook:

# in functions.php add hook & hook function
add_filter("wp_nav_menu_objects",'my_wp_nav_menu_objects_start_in',10,2);

# filter_hook function to react on start_in argument
function my_wp_nav_menu_objects_start_in( $sorted_menu_items, $args ) {
    if(isset($args->start_in)) {
        $menu_item_parents = array();
        foreach( $sorted_menu_items as $key => $item ) {
            // init menu_item_parents
            if( $item->object_id == (int)$args->start_in ) $menu_item_parents[] = $item->ID;

            if( in_array($item->menu_item_parent, $menu_item_parents) ) {
                // part of sub-tree: keep!
                $menu_item_parents[] = $item->ID;
            } else {
                // not part of sub-tree: away with it!
                unset($sorted_menu_items[$key]);
            }
        }
        return $sorted_menu_items;
    } else {
        return $sorted_menu_items;
    }
}

Next, in your template you just call wp_nav_menu with the additional start_in argument containing the ID of the page you want the children off:

wp_nav_menu( array( 
    'theme_location' => '<name of your menu>',
    'start_in' => $ID_of_page,
    'container' => false,
    'items_wrap' => '%3$s'
) );

I wrote this to print sub-navs of the pages you may be on. If you want to print out the sub-navigation for each of the pages, get the page parent instead of getting the ID. There would be more involved than that, but it's a start.

$menu = wp_get_nav_menu_items( 'Primary Menu' );
$post_ID = get_the_ID();
echo "<ul id='sub-nav'>";
foreach ($menu as $item) {
    if ($post_ID == $item->object_id) { $menu_parent = $item->ID; }
    if (isset($menu_parent) && $item->menu_item_parent == $menu_parent) {
         echo "<li><a href='" . $item->url . "'>". $item->title . "</a></li>";
     }
 }
echo "</ul>";`

Check out wp_list_pages(). It is useful for providing child navigation in the sidebar.

mac joost's answer is great, but I would add that if you want the parent item to print, then you shouldn't unset the parent, so line 18 needs to be adjusted accordingly:

    if($item->object_id != (int)$args->start_in) { unset($sorted_menu_items[$key]); }

have you seen wp_list_pages?

http://codex.wordpress.org/Function_Reference/wp_list_pages

look closer on child_of attribute

You can use Breadcrumb navxt plugin. It does exactly what you are looking for and its really great. Breadcrumb NavXT Pugin

I've stopped to explore how to output custom part of worpress site taxonomy on the server-side. I just use jquery to copy active taxonomy branch from main menu and paste it to the page container I need.

来源：https://stackoverflow.com/questions/5770884/how-to-display-part-of-a-menu-tree

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