public function get_navigation($cityid, $html_id)
 {
     APF::get_instance()->benchmark_begin(__CLASS__ . " get_navigation ");
     $key = Util_MemCacheKey::get_myanjuke_navigation($cityid);
     $memcache = APF_Cache_Factory::get_instance()->get_memcache();
     $list = $memcache->get($key);
     //        $memcache->delete($key);
     if (!$list) {
         $list = parent::get_html_content($cityid, $html_id, $key);
         $memcache->add($key, $list, 0, Util_MemCacheTime::get_myanjuke_navigation());
     }
     APF::get_instance()->benchmark_end(__CLASS__ . " get_navigation ");
     return $list;
 }