Get Custom Field Values auf Unterseiten anwenden?

/**
 * Lists pages according to the given arguments. Displays them for the sidebar
 * using custom fields.
 * 
 * @param args The arguments for retrieving the pages. Same as in function
 * wp_list_pages.
 */
function my_list_pages($args = '') {
  global $wp_query;
  
  $defaults = array(
    'depth' => 0, 'show_date' => '',
    'date_format' => get_option('date_format'),
    'child_of' => 0, 'exclude' => '',
    'title_li' => __('Pages'), 'echo' => 1,
    'authors' => '', 'sort_column' => 'menu_order, post_title'
  );
  
  $r = wp_parse_args($args, $defaults);
  extract($r, EXTR_SKIP);
  
  $output = '';
  $current_page = 0;
  
  // sanitize, mostly to keep spaces out
  $r['exclude'] = preg_replace('[^0-9,]', '', $r['exclude']);
  
  // allow plugins to filter an array of excluded pages
  $r['exclude'] = implode(',', apply_filters('wp_list_pages_excludes', explode(',', $r['exclude'])));
  
  // query pages
  $pages = get_pages($r);
  
  if (!empty($pages)) {
    if ($r['title_li']) {
      $output .= '<li class="pagenav">' . $r['title_li'] . '<ul>';
    }
    if (is_page()) {
      $current_page = $wp_query->get_queried_object_id();
    }
    
    // generate the actual output
    $walker = new My_Walker_Page;
    $output .= call_user_func_array(array(&$walker, 'walk'), array($pages, $r['depth'], $current_page, $r));
    
    if ($r['title_li']) {
      $output .= '</ul></li>';
    }
  }
  
  $output = apply_filters('wp_list_pages', $output);
  echo $output;
}

/**
 * Walker implementation, extending the standard page walker to modify the
 * output.
 */
class My_Walker_Page extends Walker_Page {
  
  /**
   * Outputs a single element of the tree. Overwritten from Walper_Page.
   */
  function start_el($output, $page, $depth, $current_page, $args) {
    // prepare
    if ($depth) {
      $indent = str_repeat("\t", $depth);
    }
    extract($args, EXTR_SKIP);
    $css_class = 'page_item page-item-'.$page->ID;
    $_current_page = get_page($current_page);
    if ($page->ID == $current_page) {
      $css_class .= ' current_page_item ';
    } else if ($_current_page && $page->ID == $_current_page->post_parent) {
      $css_class .= ' current_page_parent';
    }
    
    // get the custom field value
    $page_headline = get_post_meta($page->ID, 'my_page_headline', true);
    
    // build the output
    $output .= $indent . '<li class="' . $css_class . '">';
    if (!empty($page_headline)) {
      $output .= $indent . "\t" . '<a href="' . get_page_link($page->ID) . '" title="' . attribute_escape(apply_filters('the_title', $page->post_title)) . '"><img src="' . $page_headline . '" width="201" height="25" alt="' . attribute_escape(apply_filters('the_title', $page->post_title)) . '" title="" /></a><br />';
    } else {
      $output .= $indent . "\t" . '<a href="' . get_page_link($page->ID) . '" title="' . attribute_escape(apply_filters('the_title', $page->post_title)) . '">' . apply_filters('the_title', $page->post_title) . '</a><br />';
    }
    
    // add the date and return the output
    if (!empty($show_date)) {
      if ('modified' == $show_date) {
        $time = $page->post_modified;
      } else {
        $time = $page->post_date;
      }
      $output .= " " . mysql2date($date_format, $time);
    }
    return $output;
  }
    
}