Drupal Menu System - Outputting a Tree One Level Down

drupal, menu, tree

Solution

I always wondered why there is no function for this in core, but afaik there is none.

So it looks like we need to roll our own, walking a complete menu tree until we find the subtree we need:

/**
 * Extract a specific subtree from a menu tree based on a menu link id (mlid)
 *
 * @param array $tree
 *   A menu tree data structure as returned by menu_tree_all_data() or menu_tree_page_data()
 * @param int $mlid
 *   The menu link id of the menu entry for which to return the subtree
 * @return array
 *   The found subtree, or NULL if no entry matched the mlid
 */
function yourModule_menu_get_subtree($tree, $mlid) {
  // Check all top level entries
  foreach ($tree as $key => $element) {
    // Is this the entry we are looking for?
    if ($mlid == $element['link']['mlid'])  {
      // Yes, return while keeping the key
      return array($key => $element);
    }
    else {
      // No, recurse to children, if any
      if ($element['below']) {
        $submatch = yourModule_menu_get_subtree($element['below'], $mlid);
        // Found wanted entry within the children?
        if ($submatch) {
          // Yes, return it and stop looking any further
          return $submatch;
        }
      }
    }
  }
  // No match at all
  return NULL;
}

To use it, you first need to get the tree for the whole menu, using `menu_tree_page_data()` or `menu_tree_all_data()`, depending on what you need (check the API definitions for the difference). Then you extract the subtree you want, based on the mlid. This subtree can then be rendered into HTML via `menu_tree_output()`:

$mlid = 123; // TODO: Replace with logic to determine wanted mlid
$tree = menu_tree_page_data('navigation'); // TODO: Replace 'navigation' with name of menu you're interested in
// Extract subtree
$subtree = yourModule_menu_get_subtree($tree, $mlid);
// Render as HTML menu list
$submenu = menu_tree_output($subtree);

Disclaimer: I am not sure if this is a good/proper way to do it - it is just the solution I came up with after going through the same procedure as the OP, that is, reading through the whole menu module functions, always wondering if I'm missing the obvious somewhere...

Problem

I've been reading through the various menu functions in Drupal, but there are sooo many, and I've reached a point of utter confusion and despair... Hoping one of the smarties here can help me out... Basically, I have four levels to my menu. I'm trying to create a tree that outputs from the second level down. So, the menu looks like this: LEVEL ONE > Sublevel A > Sublevel I > Sublevel a I'm trying to output the menu tree beginning with Sublevel A (i.e., Sublevel A > Sublevel I > Sublevel a) But, can't for the life of me figure out how to do that... I tried simply getting the mlid of the Sublevel A menu (in this case 69), and then ``` <?php print theme_menu_tree(69); ?> ``` but it just prints out '69'. Not at all what I expected... Anyone know how to do this?

Original source