private void validateUser(string username, string password)
 {
     DAL.user leUser = new DAL.user();
     leUser.firstname = "Guest";
     foreach (DAL.user user in MainWindow.userVM.Users)
     {
         if (user.username.Trim() == username && user.password.Trim() == password)
         {
             leUser = user;
             break;
         }
     }
     if (leUser.firstname != "Guest")
     {
         MainWindow.CurrentUser     = leUser;
         invalidTryLabel.Visibility = Visibility.Hidden;
         showSuccess();
         win.ChangeUser();
         usernameTextBox.Clear();
         passwordBox.Clear();
         win.MainButton_Click(win.mainButton, null);
     }
     else
     {
         invalidTryLabel.Visibility = Visibility.Visible;
     }
 }