webform1.aspx

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm1.aspx.cs" Inherits="dynamicweb4_7.WebForm1" %>

<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
    <title></title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:Panel ID="plContent" runat="server">
            <h3>建议反馈</h3>
            <asp:Label ID="Label1" runat="server" Text="如对本网站有任何改进建议，请在下面输入框中填写："></asp:Label><br />
            <asp:TextBox ID="txtSuggestion" runat="server" TextMode="MultiLine" Width="350px" Height="150px"></asp:TextBox><br />
            <asp:Button ID="Button1" runat="server" Text="提交" OnClick="Button1_Click" />
        </asp:Panel>
        <asp:Panel ID="plTips" runat="server" Visible="false" Height="50" BorderStyle="Solid" BorderWidth="1">
            <h3>谢谢你的宝贵建议！</h3>
        </asp:Panel>
    </div>
    </form>
</body>
</html>

webform1.aspx.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace dynamicweb4_7
{
    public partial class WebForm1 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {

        }

        protected void Button1_Click(object sender, EventArgs e)
        {
            if (!string.IsNullOrEmpty(txtSuggestion.Text))
            {
                plContent.Visible = false;
                plTips.Visible = true;
            }
        }
    }
}