private void bt_Tim_Click(object sender, EventArgs e) { if (tb_nhucau.Text != "") { lv_dsketqua.Items.Clear(); client = new ServiceReference1.Service1Client(); client.TimnhucauCompleted+= new EventHandler<ServiceReference1.TimnhucauCompletedEventArgs>(TimnhucauCallBack); client.TimnhucauAsync(tb_nhucau.Text); } else { lv_dsketqua.Items.Clear(); client = new ServiceReference1.Service1Client(); client.LoadNHCFCompleted += new EventHandler<ServiceReference1.LoadNHCFCompletedEventArgs>(LoadNHCFCallBack); client.LoadNHCFAsync(); } }