//cek input
        guard let name = txtUsername.text, name != "",
        let emailAddress = txtEmail.text, emailAddress != "", let password = txtPassword.text, password != "" else {

            let alertController = UIAlertController(title: "Registration Error", message: "Please make sure you provide your name, email address and password to complete the registration.", preferredStyle: .alert)
            let okayAction = UIAlertAction(title: "OK", style: .cancel, handler: nil)
            alertController.addAction(okayAction)
            present(alertController, animated: true, completion: nil)

            return
        }

        FIRAuth.auth()?.createUser(withEmail: emailAddress, password: password, completion: { (user, error) in

            if let error = error {
                let alertController = UIAlertController(title: "Signup Error", message: error.localizedDescription, preferredStyle: .alert)
                let okayAction = UIAlertAction(title: "OK", style: .cancel, handler: nil)
                alertController.addAction(okayAction)
                self.present(alertController, animated: true, completion: nil)
                return
            }

            //email verification
            guard let currentUser = user, currentUser.isEmailVerified else {

                let alertController = UIAlertController(title: "Login Error", message: "please check your email and verified", preferredStyle: .alert)
                let okayAction = UIAlertAction(title: "Resend email", style: .default, handler: { (action) in
                    user?.sendEmailVerification(completion: nil)
                })
                let cancelAction = UIAlertAction(title: "Cancel", style: .cancel, handler: nil)
                alertController.addAction(okayAction)
                alertController.addAction(cancelAction)

                self.present(alertController, animated: true, completion: nil)
                return
            }

            //dismiss keyboard
            self.view.endEditing(true)
            //present the main view
            if let viewController = self.storyboard?.instantiateViewController(withIdentifier: "LoginView"){
                UIApplication.shared.keyWindow?.rootViewController = viewController
                self.dismiss(animated: true, completion: nil)
            }

        })