iframe框架下子页面刷新问题

Question

最近在使用iframe框架实现新闻页面是遇到如下问题：
新闻主页面是news.aspx,其子页面是News_inner.aspx
子页面中有一个打datalist呈现文章标题，并对标题分页
分页代码如下：
                   if (Request.QueryString["cid"] !=null)
                    {
                        int classid = Convert.ToInt32(Request.QueryString["cid"]);//classid为类别标签
                        string sql = "select ID,title = SUBSTRING(title,0,20),ModDate from rm_Article  where classid = '" + classid + "' order by ID DESC";
                        SqlDataAdapter da = new SqlDataAdapter(sql, conn);
                        DataSet ds = new DataSet();
                        da.Fill(ds);
                        PagedDataSource pds = new PagedDataSource();
                        pds.DataSource = ds.Tables[0].DefaultView;
                        pds.AllowPaging = true;//是否可以分页
                        pds.PageSize = 5;
                        int curpage;
                        if (Request.QueryString["Page"] != null)
                            curpage = Convert.ToInt32(Request.QueryString["Page"]);
                        else
                            curpage = 1;                        pds.CurrentPageIndex = curpage - 1;
                        PageShow.Text = "当前页:" + curpage.ToString();
                        if (!pds.IsFirstPage)
                            PreLink.NavigateUrl = Request.CurrentExecutionFilePath + "?Page=" + Convert.ToString(curpage - 1);
                        if (!pds.IsLastPage)
                            NextLink.NavigateUrl = Request.CurrentExecutionFilePath + "?Page=" + Convert.ToString(curpage + 1);                        TitleList.DataSource = pds;
                        TitleList.DataBind();
                    }
这样做后，只能显示第一页的标题，以后页面为空。
我调试发现，每次单机下一页时，Request.QueryString["cid"] =null ,请问大家怎么解决啊？

Answer 1

NextLink.NavigateUrl = Request.CurrentExecutionFilePath + "?cid=" + Request.QueryString["cid"] + "&Page=" + Convert.ToString(curpage + 1);