.net - How to implement file upload progress bar on web?

Question

I would like display something more meaningful that animated gif while users upload file to my web application. What possibilities do I have?

Edit: I am using .Net but I don't mind if somebody shows me platform agnostic version.

Answer 1

If you are interested how all this generally works client-site, this is it:

All the solutions hook up the form via javascript and change the forms target to a newly created, invisible IFRAME. Then they are free to use AJAX to request some status about the file from the server.

The IFRAME trick is needed because all the scripts running in the window that is doing the upload will hang until the the request is completed at which time the file is fully uploaded.