override func willMove(toParent parent: UIViewController?)
    {
        super.willMove(toParent: parent)
        if parent == nil
        {
            if UserDefaults.standard.integer(forKey: "arrayFoodSize") > 0
          && UserDefaults.standard.integer(forKey: "arrayFoodSize") != 0 {

                let alert = UIAlertController(title: "delete all item ?", message: "delete all item !?",
           preferredStyle: .alert)

                alert.addAction(UIAlertAction(title: "yes", style:
         .destructive, handler: { (UIAlertAction) in
                    let realm = try! Realm()
                    try! realm.write {
                        realm.deleteAll()
                    }

                    let lvc =
            self.storyboard?.instantiateViewController(withIdentifier:
           "res_vc") as!
          NavigationViewController


                    let appDelegate =  UIApplication.shared.delegate as!
               AppDelegate
                    appDelegate.window?.rootViewController = lvc
               nil)

                }))
                alert.addAction(UIAlertAction(title: "no", style: .cancel,
            handler: nil))

                self.present(alert, animated: true)

            }

        }