private void comboBoxEx1_SelectedIndexChanged(object sender, EventArgs e) { txtthongkeNgaySinh.Text = tkBLL.Thongke_theoNgaysinh(comboBoxTK.SelectedItem.ToString()).ToString(); tkBLL.Hienthi_TKtheoNgaySinh(lvthongkeloaikh, comboBoxTK.SelectedItem.ToString()); }