html控件select 怎么在.cs文件中对其绑定数据呢

html控件select 如何在.cs文件中对其绑定数据呢？
<select id="P_Id" runat="server"></select>
这样的一个下拉框 我以前是用DropDownList的，所以在.cs文件中有一个方法来绑定的

C# code

    private void BindProductClassData()    {        BindProductJgData();BindProductHdData();BindProductBbData();        DataTable dt = SQL.DT("select * from vProductClass order by RootID,Orders");        P_Id.Items.Clear();        DataRow[] drs = dt.Select("ParentId=0");        foreach (DataRow dr in drs)        {            string classid = dr["classid"].ToString();            string classname = dr["classname"].ToString();            classname = "├─" + classname;            P_Id.Items.Add(new ListItem(classname, classid));            int sonparentid = int.Parse(classid);            string blank = "│　";            BindDrpNode(sonparentid, dt, blank);        }        P_Id.DataBind();    }    private void BindDrpNode(int parentid, DataTable dt, string blank)    {        DataRow[] drs = dt.Select("ParentID= " + parentid);        foreach (DataRow dr in drs)        {            string classid = dr["classid"].ToString();            string classname = dr["classname"].ToString();            classname = blank + "├─" + classname;            P_Id.Items.Add(new ListItem(classname, classid));            int sonparentid = int.Parse(classid);            string blank2 = blank + "├─";            BindDrpNode(sonparentid, dt, blank2);        }    }

C# code

protected string BindDrpNode()    {        。。。。        if (reader != null)        {            while (reader.Read())            {                str += "<option value=" + reader["classid"] + ">" + reader["classname"] + "</option>";            }            reader.Close();            reader.Dispose();        }        return str;    }调用： <select id="Select1" name="Select1">            <%=BindDrpNode()%>        </select>