private void Save_Clicked(object sender, RoutedEventArgs e)
 {
     if (txtRate.Text.Length == 0)
     {
         showMessageBoxAsync();
         return;
     }
     DBEngine.AddCurrencyRating(txtCurrency.Text, txtDate.Date.Value.DateTime.ToString("yyyy-MM-dd"), txtRate.Text);
     m_parent.Hide();
 }