private void LoginInClick(object sender, RoutedEventArgs e)
        {
            string username = usernameTextBox.Text;
            string password = passwordBox.Password;

            if (helper.validate_input(username) && helper.validate_input(password))
            {
                LoginRequest  login_request = new LoginRequest(username, password);
                var           json          = new JavaScriptSerializer().Serialize(login_request);
                string        msg           = Constants.LOGIN_ID.ToString() + json.Length.ToString() + json;
                string        response      = helper.SendAndRecive(msg);
                LoginResponse loginResponse = new JavaScriptSerializer().Deserialize <LoginResponse>(response);
                if (loginResponse.status == Constants.SUCCESS_STATUS)//success status
                {
                    Helper.set_username(username);
                    MenuWindow menuWindow = new MenuWindow();
                    menuWindow.Show();
                    this.Close();
                    //MessageBox.Show("Success!");
                }
                else
                {
                    MessageBox.Show("Try again!");
                }
            }
            else
            {
                MessageBox.Show("input contain only latters and digits");
            }
        }