请教取动态生成的控件的值，有兴趣的都进来看看

文件名为test.aspx HTML代码<%@ Page Language="C#" AutoEventWireup="true" CodeFile="test.aspx.cs" Inherits="test" %><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>无标题页</title>
</head>
<body>
    <form id="form1" runat="server">
        <asp:ScriptManager ID="ScriptManager1" runat="server" />
        <div>
            <asp:Panel ID="plControls" runat="server">
            </asp:Panel>
            <br />
            &nbsp;<asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="Button"
                Width="80px" /></div>
    </form>
</body>
</html>后置文件代码using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;public partial class test : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            plcontrolsBind();
        }
    }
    private void plcontrolsBind()
    {
                Label lb = new Label();
                lb.Text = "<br> ：";
                plControls.Controls.Add(lb);
                TextBox tb = new TextBox();
                tb.Text ="文本框的值";
                plControls.Controls.Add(tb);
                RadioButton rb = new RadioButton();
                rb.Text ="rb1的值";
                rb.GroupName ="group";
                plControls.Controls.Add(rb);
                RadioButton rb2 = new RadioButton();
                rb2.Text = "rb2的值";
                rb2.GroupName = "group";
                plControls.Controls.Add(rb2);
                CheckBox ck = new CheckBox();
                ck.Text = "复选框ck";
                plControls.Controls.Add(ck);
                CheckBox ck1= new CheckBox();
                ck1.Text = "复选框ck1";
                plControls.Controls.Add(ck1);
                CheckBox ck2 = new CheckBox();
                ck2.Text = "复选框2ck";
                plControls.Controls.Add(ck2);
            }    protected void Button1_Click(object sender, EventArgs e)
    {
        foreach (Control ct in plControls.Controls)
        {
            string result = "";
            if (ct is TextBox)
            {
                result = ((TextBox)ct).Text;
            }
            if (ct is RadioButton)
            {
                foreach (ListItem lt in ((RadioButtonList)ct).Items)
                {
                    if (lt.Selected == true)
                    {
                        result = ((RadioButton)ct).Text+"被选中了";
                    }
                }
            }            if (ct is CheckBoxList)
            {
                string s = "";
                foreach (ListItem lt in ((CheckBoxList)ct).Items)
                {
                    if (lt.Selected == true)
                    {
                        result = ((CheckBox)ct).Text+"被选中了";
                    }
                }
            }
            Page.RegisterStartupScript("aaa", "<script>alert('"+result+"')</script>");
        }
    }
}问题：在Button点击事件Button1_Click为什么取不到控件的值，理论上应该没问题
哪位能告诉下忽视了什么地方