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