File Uploading without page refresh in Web pages

Hii,

Any one knows how to upload files to the physical location of the server. It is possible using file upload control that i know. But i want to avoid the external postbacking of the page. For e.g exactly like what in the yahoo mail did.

In yahoo mail latest version if you attach a file that won't post back and attach that file in to se开发者_StackOverflow社区rver. What is the technology behind that?

Normally when you submit a form it does a POST request to the server, causing a refresh. Ajax requests get round this by using JavaScript to send the POST data through to the server, and that doesn't need a page refresh.

Ajax requests can't be used to send file data though, so the best way to currently do it is with an iframe hack - you use JavaScript to dynamically build up a form within an iframe, submit that form via JavaScript, and listen for the iframe's onload event. So you know when the form has been submitted. A version of this approach is detailed here:

http://www.webtoolkit.info/ajax-file-upload.html

Other methods to do this would include using a Flash-based solution like http://www.swfupload.org/ or a wrapper like http://www.plupload.com/ - these will prevent you having to roll your own solution and will also provide some extra functionality - upload progress feedback, for example.