private void Button_Registration(object sender, RoutedEventArgs e) { if (manager.CheckUser(textBoxPhone.Text) == null) { var user = new User { Name = textBoxName.Text }; if (user.IsValid() && CheckPhoneFormat(textBoxPhone.Text) && ConfirmPassword(regPassword_1.Password, regPassword_2.Password)) { user.Phone = textBoxPhone.Text; user.CarPlateNumber = textCarPlate.Text; user.Password = regPassword_1.Password; manager.AddUser(user); MessageBox.Show("You have been successfully registered. Log in now."); Close(); } else { MessageBox.Show("Incorrect name, phone number format or passwords don't match. Try again."); } } else { MessageBox.Show("You've signed up earlier"); } }