动态创建HtmlTable的问题

public partial class Sys_PowerEdit : Oplink.Web.UI.OplinkPage
    {
        System.Web.UI.HtmlControls.HtmlTableRow _htmlTr = new HtmlTableRow(); //<tr>行
        System.Web.UI.HtmlControls.HtmlTableCell _htmlTd1 = new HtmlTableCell("td");
        System.Web.UI.HtmlControls.HtmlTableCell _htmlTd2 = new HtmlTableCell("td");
        System.Web.UI.HtmlControls.HtmlTableCell _htmlTd3 = new HtmlTableCell("td");
        System.Web.UI.HtmlControls.HtmlTableCell _htmlTd4 = new HtmlTableCell("td");
        System.Web.UI.HtmlControls.HtmlTableCell _htmlTd5 = new HtmlTableCell("td");
        System.Web.UI.HtmlControls.HtmlTableCell _htmlTd6 = new HtmlTableCell("td");
        System.Web.UI.HtmlControls.HtmlTableCell _htmlTd7 = new HtmlTableCell("td");

        System.Web.UI.HtmlControls.HtmlTableRow _htmlTrItem;
        System.Web.UI.HtmlControls.HtmlTableCell _htmlTdItem1;
        System.Web.UI.HtmlControls.HtmlTableCell _htmlTdItem2;
        System.Web.UI.HtmlControls.HtmlTableCell _htmlTdItem3;
        System.Web.UI.HtmlControls.HtmlTableCell _htmlTdItem4;
        System.Web.UI.HtmlControls.HtmlTableCell _htmlTdItem5;
        System.Web.UI.HtmlControls.HtmlTableCell _htmlTdItem6;
        System.Web.UI.HtmlControls.HtmlTableCell _htmlTdItem7;


        string _strNode, _strValue;
        string _selNode="";

        public string[] _imgprex = new string[] { "Qry", "Add", "Upn", "Del", "Prn"};

        protected void Page_Load(object sender, EventArgs e)
        {
            CreateTableHeader();
        }

        
        private TreeNode FindNode(TreeNode tnParent, string strValue)
        {

            if (tnParent == null) return null;

            if (tnParent.Text == strValue) return tnParent;



            TreeNode tnRet = null;

            foreach (TreeNode tn in tnParent.ChildNodes)
            {

                tnRet = FindNode(tn, strValue);

                if (tnRet != null) break;

            }

            return tnRet;

        }

        protected void TreeView1_SelectedNodeChanged(object sender, EventArgs e)
        {
            
            int _imgIdx;