webform1.aspx

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm1.aspx.cs" Inherits="test17_4.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:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager>
    </div>
    <asp:UpdatePanel ID="UpdatePanel1" runat="server">
        <ContentTemplate>
            <div style="background-color:#ffffe0;padding:20px;">
                <asp:Label ID="lblTime" runat="server" Text="" Font-Bold="true"></asp:Label>
                <br /><br />
                <asp:Button ID="btnRefreshTime" runat="server" Text="申请刷新" OnClick="btnRefreshTime_Click"/>
            </div>
        </ContentTemplate>
    </asp:UpdatePanel>
    <br />
        <asp:UpdateProgress ID="UpdateProgress1" runat="server">
            <ProgressTemplate>
                <div style="font-size:small">
                    正在连接服务器......
                    <img  src="wait.gif" alt="等待"/>
                </div>
            </ProgressTemplate>
        </asp:UpdateProgress>
    </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 test17_4
{
    public partial class WebForm1 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {

        }

        protected void btnRefreshTime_Click(object sender, EventArgs e)
        {
            System.Threading.Thread.Sleep(TimeSpan.FromSeconds(10));
            lblTime.Text = DateTime.Now.ToLongTimeString();
        }
    }
}