protected void GridView1_RowSelect(object sender, GridViewSelectEventArgs e)
{
DDatHangDTO ddhDTO = new DDatHangDTO();
ddhDTO.MaHD = int.Parse(GridView1.DataKeys[e.NewSelectedIndex]["MaHD"].ToString());
DataTable dt = DDatHangBUS.LayChiTietHoaDon(ddhDTO);
GridView2.DataSource = dt;
GridView2.DataBind();
}