private void tbxUsername_TextChanged(object sender, TextChangedEventArgs e) { var textbox = sender as TextBox; var input = textbox.Text; LoginValidation loginValidation = new LoginValidation(); bool isUsernameAvailable = true; try { isUsernameAvailable = loginValidation.IsUsernameAvailable(input); } catch (Exception ex) { MessageBox.Show(ex.Message.ToString()); } if (isUsernameAvailable) { ImgAcceptMark.Visibility = Visibility.Visible; tbxUsername.Foreground = Brushes.Black; gotUsername = true; } else { ImgAcceptMark.Visibility = Visibility.Hidden; tbxUsername.Foreground = Brushes.Red; gotUsername = false; } }