private void FindButton_Click(object sender, RoutedEventArgs e)
{
gridControl1.ShowLoadingPanel = true;
gridControl1.ItemsSource = null;
QLThuebaoDomainContext dstb = new QLThuebaoDomainContext();
InvokeOperation<System.Nullable<int>> p = dstb.Excute_p_tklydocat(dngaybd.DateTime, dngaykt.DateTime);
p.Completed += new EventHandler(Completed);
}