public static function get_instance()
 {
     if (self::$instance === null) {
         self::$instance = new QHShopWidgetCategory();
     }
     return self::$instance;
 }
 public static function run()
 {
     $instance = self::get_instance();
     //start session
     QHShopSession::run();
     //start qhshop proudct
     QHShopProduct::run();
     //start shortcode
     QHShopShortCode::run();
     //start setting
     QHShopSetting::run();
     //run widget cart
     QHShopWidgetCart::run();
     //khoi dong order
     QHShopOrder::run();
     //run widget category
     QHShopWidgetCategory::run();
     return $instance;
 }