ASP.NET FileUpload Control Inside an UpdatePanel

I put a FileUpload control inside an UpdatePanel and ran into some problems, as many others did.

Since the UpdatePanel does not do a full postback by nature (and therefore only partially refreshes the screen), the FileUpload control does not work straight away.

To get it to work you need to add a PostBackTrigger which points at your Upload button. Here's a Microsoft example on that very topic.

Using a PostBackTrigger will cause a full postback to fire when a file is uploaded and will cause your control to work... in most cases.

However I found an odd issue where the file upload did not work the first time (the FileUpload control's HasFile property was always False) but it would upload successfully the second time.

I had to root around in a few places and eventually found the answer on StackOverflow's forums.

Turns out the answer is to define this in your Page_Load event:

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

Page.Form.Enctype = "multipart/form-data"

End Sub

After I added this, the FileUpload control started to work every time.