asp.net panel 动态加载控件

前台:
<asp:Panel ID = "pnlCondition" runat="server"  Width = "100%">
</asp:Panel>

后台:LiteralControl lc = null;
    DropDownList ddl = null;
    Label lbl = null;
    TextBox txt = null;  //定义为全局

//加载

            DataTable dtKeyInfo = DB.ExecuteDataSet(dc).Tables[0];  //得到配置表中每个栏位的定义
            lc = new LiteralControl("<table>");
            pnlCondition.Controls.Add(lc);
            for (int i = 0; i < dtKeyInfo.Rows.Count; i++)
            {
                lc = new LiteralControl("<tr>");
                pnlCondition.Controls.Add(lc);
                lc = new LiteralControl("<td class='Field_Label'>");
                pnlCondition.Controls.Add(lc);
                lbl = new Label();
                lbl.ID = i.ToString();
                lbl.Text = dtKeyInfo.Rows[i]["fieldname"].ToString();
                pnlCondition.Controls.Add(lbl);
                lc = new LiteralControl("</td>");
                pnlCondition.Controls.Add(lc);
                lc = new LiteralControl("<td>");
                pnlCondition.Controls.Add(lc);
                string column = dtKeyInfo.Rows[i]["fieldname"].ToString();
                if (dtKeyInfo.Rows[i]["uitype"].ToString() == "ddl")
                {
                    
                    ddl = new DropDownList();
                    ddl.ID = column;
                    this.BindDDl(ddl,column);
                    pnlCondition.Controls.Add(ddl);
                }
                if (dtKeyInfo.Rows[i]["uitype"].ToString() == "txt")
                {
                    txt = new TextBox();
                    txt.ID = column;
                    txt.MaxLength = 10;
                    pnlCondition.Controls.Add(txt);
                }
                lc = new LiteralControl("</td>");
                pnlCondition.Controls.Add(lc);
                lc = new LiteralControl("</tr>");
                pnlCondition.Controls.Add(lc);
            }
            lc = new LiteralControl("</table>");
            pnlCondition.Controls.Add(lc);