ASP.NET FileUpload: how to automatically post back once a file is selected?

Question

I am working on a ASP.NET app and i have a need to post back to the server after a file is chosen in a FileUpload control without having to have the user explicitly click a 'submit' button. Is this possible? and if so, how?

Answer 1

I'm assuming you want to make the upload start right away. If so, you should react to the change event in JavaScript, and simply make it submit the form.

<!-- HTML code --->
<input 
  type="file" 
  onchange="if (confirm('Upload ' + this.value + '?')) this.form.submit();"
>

Asking the users for confirmation is recommendable, so they stay in control of the process and can cancel if they chose the wrong file by accident.

Answer 2

The first answer had the right javascript, but ASP.NET does not necessarily expose the input control directly, so it is better to put the onchange event on the FileUpload control.

<asp:FileUpload ID="myFileUpload" onchange="if (confirm('Upload ' + this.value + '?')) this.form.submit();" runat="server" />

Another route to go is to provide rich uploading via flash/silverlight/ajax. A great component for this can be found at http://www.ajaxuploader.com/ for about $100 or there is a free one at http://www.swfupload.org/ that requires a little more effort to implement.