Add custom markup to Wordpress menu

Question

I've been search for a long time now for a solution to this problem but found nothing so you guys will be my last hope!

I'm trying to build a new CSS3 menu on a Wordpress 3 site that I'm working on. I would need to extend the default menu mark-up but not sure how.

This is the tag I'm using in the theme to output the menu at the moment:

<?php wp_nav_menu( array( 'container_class' => 'menu-header', 'theme_location' => 'primary' ) ); ?>

At the moment my default menu mark-up looks like this:

<div class="menu-header">
 <ul id="menu-main-menu" class="menu">
  <li id="menu-item-62" class="menu-item menu-item-type-post_type current-menu-item page_item page-item-43 current_page_item menu-item-62"><a href="#">Top Level Menu Item</a></li>
  <li id="menu-item-70" class="menu-item menu-item-type-post_type menu-item-70"><a href="#">Top Level Menu Item</a>
   <ul class="sub-menu">
    <li id="menu-item-71" class="menu-item menu-item-type-taxonomy menu-item-71"><a href="#">Sub Level Menu Item</a></li>
   </ul>
  </li>
  <li id="menu-item-220" class="menu-item menu-item-type-post_type menu-item-220"><a href="#">Top Level Menu Item</a></li>
  <li id="menu-item-129" class="menu-item menu-item-type-post_type menu-item-129"><a href="#">Top Level Menu Item</a>
   <ul class="sub-menu">
    <li id="menu-item-206" class="menu-item menu-item-type-post_type menu-item-206"><a href="#">Sub Level Menu Item</a></li>
    <li id="menu-item-207" class="menu-item menu-item-type-post_type menu-item-207"><a href="#">Sub Level Menu Item</a></li>
    <li id="menu-item-200" class="menu-item menu-item-type-post_type menu-item-200"><a href="#">Sub Level Menu Item</a></li>
   </ul>
  </li>
  <li id="menu-item-243" class="menu-item menu-item-type-post_type menu-item-243"><a href="#">Top Level Menu Item</a></li>
 </ul>
</div>

I need to add 2 div's around each <ul class="sub-menu">...</ul> So I would need the mark-up to look like this:

<div class="menu-header">
 <ul id="menu-main-menu" class="menu">
  <li id="menu-item-62" class="menu-item menu-item-type-post_type current-menu-item page_item page-item-43 current_page_item menu-item-62"><a href="#">Top Level Menu Item</a></li>
  <li id="menu-item-70" class="menu-item menu-item-type-post_type menu-item-70"><a href="#">Top Level Menu Item</a>
   <div class="sub-menu-container">
    <div class="submenu">
     <ul class="sub-menu">
      <li id="menu-item-71" class="menu-item menu-item-type-taxonomy menu-item-71"><a href="#">Sub Level Menu Item</a></li>
     </ul>
    </div>
   </div>
  </li>
  <li id="menu-item-220" class="menu-item menu-item-type-post_type menu-item-220"><a href="#">Top Level Menu Item</a></li>
  <li id="menu-item-129" class="menu-item menu-item-type-post_type menu-item-129"><a href="#">Top Level Menu Item</a>
   <div class="sub-menu-container">
    <div class="submenu">
     <ul class="sub-menu">
      <li id="menu-item-206" class="menu-item menu-item-type-post_type menu-item-206"><a href="#">Sub Level Menu Item</a></li>
      <li id="menu-item-207" class="menu-item menu-item-type-post_type menu-item-207"><a href="#">Sub Level Menu Item</a></li>
      <li id="menu-item-200" class="menu-item menu-item-type-post_type menu-item-200"><a href="#">Sub Level Menu Item</a></li>
     </ul>
    </div>
   </div>
  </li>
  <li id="menu-item-243" class="menu-item menu-item-type-post_type menu-item-243"><a href="#">Top Level Menu Item</a></li>
 </ul>
</div>

Does anyone know how to do this please?

Answer 1

According the Wordpress documentation http://codex.wordpress.org/Function_Reference/wp_nav_menu#Example, just add a Walker to the menu:

<?php wp_nav_menu( array(
    'container_class'=>'menu-header',
    'theme_location'=>'primary',
    'walker'=>new my_Walker_Menu_List() //This is the trick!
)); ?>

And then in your theme's functions.php file add the following code:

class my_Walker_MegaMenu extends Walker_Nav_Menu{
    /**
     * @see Walker::start_lvl()
     * @since 3.0.0
     *
     * @param string $output Passed by reference. Used to append additional content.
     * @param int $depth Depth of page. Used for padding.
     */
    function start_lvl( &$output, $depth = 0, $args = array() ) {
        $indent = str_repeat("\t", $depth);
        //$output .= "\n$indent<ul class=\"sub-menu\">\n"; //this is default output;

        //if( $depth==0 ) //'0'==>1st-sub-level; '1'=2nd-sub-level; ....
        $output .= "\n$indent<div class=\"sub-menu-container\"><div class=\"submenu\"><ul class=\"sub-menu\">\n";
    }

    /**
     * @see Walker::end_lvl()
     * @since 3.0.0
     *
     * @param string $output Passed by reference. Used to append additional content.
     * @param int $depth Depth of page. Used for padding.
     */
    function end_lvl( &$output, $depth = 0, $args = array() ) {
        $indent = str_repeat("\t", $depth);
        //$output .= "$indent</ul>\n"; //this is default output;

        //if( $depth==0 ) //'0'==>1st-sub-level; '1'=2nd-sub-level; ....
        $output .= "$indent</ul></div></div>\n";
    }
}

Conditionally, we can check the value of $depth to output custom markup only for desired sub-level(s);

For more information, you can see: http://shinraholdings.com/62/custom-nav-menu-walker-function/#example-code

Answer 2

The menu markup is generated in wp-includes/classes.php with Walker class, specifically class Walker_Page extends Walker {

If you look through the functions in the class you can see where the actual markup is generated.

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