程序中有时会因要执行业务比较复杂, 运行时间长的一系统操作, 需要显示如 "执行中 .." 等用户友好提示,  可用ASP.NET AJAX 的 UpdatePanel & UpdateProgress 控件完成. 但若执行结果需要下载文件时, 则会出现执行完成但文件却下载不了的情况. 因为 UpdateProgress 是异步进行中.  解决方法可以建立一个 'DownloadFile.aspx' 页面作辅助, 请见如下主要代码片断  

-------  Data.aspx ----------- 

<asp:ScriptManager ID="ScriptManager" runat="server" /> 

<asp:UpdatePanel ID="UpdatePanel1" runat="server">
        <ContentTemplate> 

               <asp:UpdateProgress ID="UpdateProgress1" runat="server" DisplayAfter="2" DynamicLayout="true">
                            <ProgressTemplate>
                                <img src='<%=CommonUrl.Images %>wait_clock.gif' />
                                <span id='spanProgressNote'></span>
                            </ProgressTemplate>
              </asp:UpdateProgress>

         </ContentTemplate>
</asp:UpdatePanel>  

 <script language="javascript">

        Sys.WebForms.PageRequestManager.getInstance().add_initializeRequest(initializeRequestHandler);

        function initializeRequestHandler(sender, e) {
            var postBackElementId = e.get_postBackElement().id;

            switch (postBackElementId) {
                case '<%= btnSearch.ClientID %>':
                    spanProgressNote.innerHTML = 'Loading ..';
                    break;

                case '<%= imgExport.ClientID %>':
                    spanProgressNote.innerHTML = 'Exporting ..';
                    break;
              }                      

         }       

</script>

-------  Data.cs ----------- 

protected void imgExport_Click(object sender, ImageClickEventArgs e)
 {
        ...

       // SimpleWebUtils.DownloadFile(Response, filePath, Path.GetFileName(filePath));     // 不能直接在当前页下载文件 

        ScriptManager.RegisterStartupScript(this, this.GetType(), "RegisterStartupScript"
                                                , String.Format("window.navigate('../Control/'DownloadFile.aspx?path={0}');", Server.UrlEncode(filePath)), true);

        //ScriptManager.RegisterStartupScript(this, this.GetType(), "RegisterStartupScript"
        //                                       , String.Format("window.navigate('{0}');", fileUrl), true);      // 用这种方式可以不用 ''DownloadFile.aspx' 页面但下载文件直接打开是用网页方式而不是实际文件方式 (如: Excel)

 }

-------  DownloadFile.cs -----------

 protected void Page_Load(object sender, EventArgs e)
 {
        string path = Request.QueryString["path"];
        SimpleWebUtils.DownloadFile(Response, path, Path.GetFileName(path));
        ScriptManager.RegisterStartupScript(this, this.GetType(), "RegisterStartupScript", "window.close();", true);                                                
 }