gridview排序

private void GetDataTablefenye()
        {
            string srotexp = string.Empty;
            if (ViewState["sortexp"] != null)
            {
                Dictionary<string, string> dic = (Dictionary<string, string>)ViewState["sortexp"];

                foreach (KeyValuePair<string, string> keyvalue in dic)
                {
                    srotexp += "," + keyvalue.Key + " " + keyvalue.Value;
                }
                srotexp = srotexp.Substring(1);
            }
            ArticleInfo article = new ArticleInfo();
            this.GridView1.DataSource = article.GetDataTablefenye(Convert.ToInt32(ViewState["pageindex"]),pagesize,srotexp);
            this.GridView1.DataBind();
        }
        protected void GridView1_Sorting(object sender, GridViewSortEventArgs e)
        {

            Dictionary<string, string> dic = new Dictionary<string, string>();
            if (ViewState["sortexp"] == null)
            {
                dic.Add(e.SortExpression, "ASC");
                ViewState["sortexp"] = dic;
            }
            else
            {
                dic = (Dictionary<string, string>)ViewState["sortexp"];
                if (dic.ContainsKey(e.SortExpression))
                {
                    if (dic[e.SortExpression] == "ASC")
                    {
                        dic[e.SortExpression] = "DESC";
                    }
                    else
                    {
                        dic[e.SortExpression] = "ASC";
                    }
                    ViewState["sortexp"] = dic;

                }
                else
                {
                    dic.Clear();
                    dic.Add(e.SortExpression, "ASC");
                    ViewState["sortexp"] = dic;
                }
            }
            GetDataTablefenye();
        }