asp.net Gridview分页保存选项

#region //'Revision: 1.00 Created Date: 2013/08/02 Created ID: Una [#1300071]增加多選框
        /// summary>
        /// Session獲取多選框值
        /// /summary>
        private void RememberOldValues()
        {
            ArrayList categoryIDList = new ArrayList();
            string index = "";
            foreach (GridViewRow row in gridView.Rows)
            {
                index = (string)gridView.DataKeys[row.RowIndex].Value;
                bool result = ((CheckBox)row.FindControl("DeleteThis")).Checked;

                // Check in the Session
                if (Session["id"] != null)
                    categoryIDList = (ArrayList)Session["id"];
                if (result)
                {
                    if (!categoryIDList.Contains(index))
                        categoryIDList.Add(index);
                }
                else
                    categoryIDList.Remove(index);
            }
            if (categoryIDList != null categoryIDList.Count > 0)
                Session["id"] = categoryIDList;
        }

        /// summary>
        /// Session分頁時之前多選框為true
        /// /summary>
        private void RePopulateValues()
        {
            ArrayList categoryIDList = (ArrayList)Session["id"];
            if (categoryIDList != null categoryIDList.Count > 0)
            {
                foreach (GridViewRow row in gridView.Rows)
                {
                    string index = (string)gridView.DataKeys[row.RowIndex].Value;
                    if (categoryIDList.Contains(index))
                    {
                        CheckBox myCheckBox = (CheckBox)row.FindControl("DeleteThis");
                        myCheckBox.Checked = true;
                    }
                }
            }
        }
        #endregion

protected void gridView_PageIndexChanging(object sender, GridViewPageEventArgs e)
        {
            RememberOldValues();
            gridView.PageIndex = e.NewPageIndex;
            BindData();
            RePopulateValues();
        }

protected void btnSelect_Click(object sender, EventArgs e)
        {
            string items = "";
            ArrayList categoryIDList = new ArrayList();
            string index ="";
            foreach (GridViewRow row in gridView.Rows)
            {
                index = (string)gridView.DataKeys[row.RowIndex].Value;
                bool result = ((CheckBox)row.FindControl("DeleteThis")).Checked;

                // Check in the Session
                if (Session["id"] != null)
                    categoryIDList = (ArrayList)Session["id"];
                if (result)
                {
                    if (!categoryIDList.Contains(index))
                        categoryIDList.Add(index);
                }
                else
                    categoryIDList.Remove(index);
            }
            if (categoryIDList != null categoryIDList.Count > 0)
                for (int i = 0; i categoryIDList.Count; i++)
                {
                    items += categoryIDList[i] + ",";
                }
            items = items.Substring(0, items.Length - 1);
            ScriptManager.RegisterStartupScript(this, this.GetType(), "", "check('" + items + "');", true);
            Session.Remove("id");
        }