private void textAmount_TextChanged(object sender, TextChangedEventArgs e) { decimal amount; if (decimal.TryParse(textAmount.Text, out amount)) { try { labelFee.Content = Wallet.CalcFee(amount).ToString(); buttonSend.IsEnabled = true; } catch (Exception ex) { labelFee.Content = ex.Message; buttonSend.IsEnabled = false; } } else buttonSend.IsEnabled = false; }