在ASP.NET中如何检测文件下载完成?

I have a popup window that displays "Please wait while your file is being downloaded". This popup also executes the code below to start the file download. How can I close the popup window once the file download has completed? I need some way to detect that the file download has completed so I can call self.close() to close this popup.I have a popup window that displays "Please wai