protected void data_RowCommand(object sender, GridViewCommandEventArgs e)
 {
     if (e.CommandName == "Sua")
     {
         id = (string)e.CommandArgument;
         Response.Redirect("suachuyenmuc.aspx?id=" + id);
     }
     else
     {
         id = (string)e.CommandArgument;
         DanhMucDAO DAO = new DanhMucDAO();
         DAO.XoaDanhMuc(id);
         LoadDuLieu();
     }
 }