private void onSignUp()
        {
            user.Username = username;
            user.Password = password;

            if (!string.IsNullOrEmpty(user.Username) && !string.IsNullOrEmpty(user.Password))
            {
                _validateUserService.userSignIn(user);
                App.Current.MainPage.DisplayAlert("User added", "You can log in", "Ok");
                _navigation.NavigateAsync(nameof(LoginView));
            }
            else
            {
                App.Current.MainPage.DisplayAlert("Error", "Fill in all fields", "Ok");
            }
        }