<form id="form1" runat="server">
        <asp:ScriptManager ID="ScriptManager1" runat="server">
        </asp:ScriptManager>
        <div>
            <asp:UpdatePanel ID="UpdatePanel1" runat="server">
                <ContentTemplate>
                    <asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" />
                </ContentTemplate>
            </asp:UpdatePanel>
            <asp:UpdateProgress ID="UpdateProgress1" runat="server" AssociatedUpdatePanelID="UpdatePanel1"> 
                <ProgressTemplate>
                    请稍候......
                </ProgressTemplate>
            </asp:UpdateProgress>
        </div>
    </form>

        Response.Write("<div id='mydiv' >");
        Response.Write("_");
        Response.Write("</div>");
        Response.Write("<script>mydiv.innerText = '';</script>");
        Response.Write("<script language=javascript>;");
        Response.Write("var dots = 0;var dotmax = 10;function ShowWait()");
        Response.Write("{var output; output = '正在装载页面';dots++;if(dots>=dotmax)dots=1;");
        Response.Write("for(var x = 0;x < dots;x++){output += '.';}mydiv.innerText =  output;}");
        Response.Write("function StartShowWait(){mydiv.style.visibility = 'visible'; ");
        Response.Write("window.setInterval('ShowWait()',1000);}");
        Response.Write("function HideWait(){mydiv.style.visibility = 'hidden';");
        Response.Write("window.clearInterval();}");
        Response.Write("StartShowWait();</script>");
        Response.Flush();//这一句是最关键的