Display only page specific sub menu items using Custom Walker

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I’ve just implemented the technique described at http://wordpress.org/support/topic/wp_nav_menu-list-only-2nd-level-separate-submenu/page/2 when implementing a theme for a client. When I run the theme locally on my WordPress stack it behaves as expected displaying only the children of the parent menu item. When I deploy this to the server it displays all menu items including parents and children which obviously isn’t the desired result. My code is as follows:-

From functions.php:-

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class Custom_Walker_Nav_Sub_Menu extends Walker_Nav_Menu {

  var $found_parents = array();

function start_el(&$output, $item, $depth, $args) {

        global $wp_query;

        //this only works for second level sub navigations
        $parent_item_id = 0;

        $indent = ( $depth ) ? str_repeat( "t", $depth ) : '';

        $class_names = $value = '';

        $classes = empty( $item->classes ) ? array() : (array) $item->classes;  

        $class_names = join( ' ', apply_filters( 'nav_menu_css_class', array_filter( $classes ), $item ) );
        $class_names = ' class="' . esc_attr( $class_names ) . '"';


     if ( ($item->menu_item_parent==0) && (strpos($class_names, 'current-menu-parent')) ) { 
         $output.= '
<li>';
         }


        // Checks if the current element is in the current selection
        if (strpos($class_names, 'current-menu-item')
            || strpos($class_names, 'current-menu-parent')
            || strpos($class_names, 'current-menu-ancestor')
            || (is_array($this->found_parents) && in_array( $item->menu_item_parent, $this->found_parents )) ) {

            // Keep track of all selected parents
            $this->found_parents[] = $item->ID;

            //check if the item_parent matches the current item_parent
            if($item->menu_item_parent!=$parent_item_id){

                $output .= $indent . '<li id="menu-item-'. $item->ID . '"' . $value . $class_names .'>';

                $attributes  = ! empty( $item->attr_title ) ? ' title="'  . esc_attr( $item->attr_title ) .'"' : '';
                $attributes .= ! empty( $item->target )     ? ' target="' . esc_attr( $item->target     ) .'"' : '';
                $attributes .= ! empty( $item->xfn )        ? ' rel="'    . esc_attr( $item->xfn        ) .'"' : '';
                $attributes .= ! empty( $item->url )        ? ' href="'   . esc_attr( $item->url        ) .'"' : '';

                $item_output = $args->before;
                $item_output .= '<a'. $attributes .'>';
                $item_output .= $args->link_before . apply_filters( 'the_title', $item->title, $item->ID ) . $args->link_after;
                $item_output .= '</a>';
                $item_output .= $args->after;

                $output .= apply_filters( 'walker_nav_menu_start_el', $item_output, $item, $depth, $args );
            }


        }
    }

    function end_el(&$output, $item, $depth) {
      // Closes only the opened li
      if ( is_array($this->found_parents) && in_array( $item->ID, $this->found_parents ) ) {
          $output .= "</li>n";
    }
  }

  function end_lvl(&$output, $depth) {
    $indent = str_repeat("t", $depth);
    // If the sub-menu is empty, strip the opening tag, else closes it
    if (substr($output, -22)=="<ul class="sub-menu">n") {
      $output = substr($output, 0, strlen($output)-23);
    } else {
      $output .= "$indent</ul>n";
    }
  }

}

From the template:- 

<!-- start navigation -->
<div id="nav">
<div id="page-navigation">

    <?php wp_nav_menu( array('theme_location' => 'primary', 'menu_class' => 'nav-menu', 'container' => '', 'depth' => 1,  )); ?>
</div>  
<div id="subnav">
    <?php
    $menu_args = array(
  'walker'          => new Custom_Walker_Nav_Sub_Menu(),
  'container'       => '',
  'menu_class'      => 'sister-pages',
s);
wp_nav_menu($menu_args);
?>
</div>
</div>
<!-- end navigation -->

The generated source:- 

<!-- start navigation -->
<div id="nav">
<div id="page-navigation">
<ul id="menu-main-menu" class="nav-menu">
<li id="menu-item-6931" class="menu-item menu-item-type-custom menu-item-object-custom current-menu-item current_page_item menu-item-home">
<a href="http://www.landlordreferencing.co.uk/">Our Products</a>
</li>
<li id="menu-item-6891" class="menu-item menu-item-type-custom menu-item-object-custom">
<a href="/wp-login.php?redirect_to=%2Fexisting-members%2F">Existing Members</a>
</li>
<li id="menu-item-6884" class="menu-item menu-item-type-custom menu-item-object-custom">
<a href="/business-directory/">Business Directory</a>
</li>
</ul>
</div>
<div id="subnav">
<ul id="menu-main-menu-1" class="sister-pages">
<li id="menu-item-6931" class="menu-item menu-item-type-custom menu-item-object-custom current-menu-item current_page_item menu-item-home">
<a href="http://www.landlordreferencing.co.uk/">Our Products</a>
<ul class="sub-menu">
<li style="display:none;"></li>
<li id="menu-item-6886" class="menu-item menu-item-type-post_type menu-item-object-page">
<a href="http://www.landlordreferencing.co.uk/home-2/">Overview</a>
</li>
<li id="menu-item-6888" class="menu-item menu-item-type-post_type menu-item-object-page">
<a href="http://www.landlordreferencing.co.uk/tenant-lifestyle-referencing/">Tenant Lifestyle Referencing</a>
</li>
<li id="menu-item-6920" class="menu-item menu-item-type-post_type menu-item-object-page">
<a href="http://www.landlordreferencing.co.uk/tenant-credit-referencing/">Tenant Credit Referencing</a>
</li>
<li id="menu-item-6889" class="menu-item menu-item-type-post_type menu-item-object-page">
<a href="http://www.landlordreferencing.co.uk/insurance/">Insurance</a>
</li>
</ul>
</li>
<li id="menu-item-6891" class="menu-item menu-item-type-custom menu-item-object-custom">
<a href="/wp-login.php?redirect_to=%2Fexisting-members%2F">Existing Members</a>
<ul class="sub-menu">
<li style="display:none;"></li>
<li id="menu-item-6912" class="menu-item menu-item-type-post_type menu-item-object-page">
<a href="http://www.landlordreferencing.co.uk/register-a-tenant/">Register a Tenant</a>
</li>
<li id="menu-item-6925" class="menu-item menu-item-type-post_type menu-item-object-page">
<a href="http://www.landlordreferencing.co.uk/tenant-search/">Tenant Lifestyle Search</a>
</li>
<li id="menu-item-6903" class="menu-item menu-item-type-post_type menu-item-object-page">
<a href="http://www.landlordreferencing.co.uk/access-experian/">Tenant Credit Search</a>
</li>
<li id="menu-item-6930" class="menu-item menu-item-type-custom menu-item-object-custom">
<a href="/questions/">Discuss</a>
</li>
</ul>
</li>
<li id="menu-item-6884" class="menu-item menu-item-type-custom menu-item-object-custom">
<a href="/business-directory/">Business Directory</a>
</li>
</ul>
</div>
</div>
<!-- end navigation -->
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1 comment

  1. Here is a much simpler implementation:

    class UL_Submenu_Walker extends Walker_Nav_Menu {
    private $hidden = false;

    function start_lvl(&$output, $depth) {
        if($depth == 0) {
            $style = $this->hidden ? "" : "display:none;";
        }
        $output .= "<ul class="submenu-".$depth."" style='".$style."'>";
    }

    function start_el(&$output, $item, $depth, $args) {
        $class_names = $value = '';

        $classes = empty( $item->classes ) ? array() : (array) $item->classes;  

        if ($depth == 0 &&
                (in_array("current-menu-item", $classes) ||
                 in_array('current-menu-parent', $classes) ||
                 in_array('current-menu-ancestor', $classes)) ) {
            $this->hidden = true;
        } else {
            $this->hidden = false;
        }
        parent::start_el($output, $item, $depth, $args);
    }
}

    I’m sure this will need some optimization, but it works.