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); }