File Upload weirdness...




So, I'm a .NET/AJAX web application (VB.NET) and in one of my content
screens, among a barrage of controls and panels, I have a File Upload
control... nothing fancy.
Below the control there is a standard button called aFile_btn.

This is the click event of aFile_btn:
Protected Sub aFile_btn_Click(ByVal sender As Object, ByVal e As
If FileUpload1.PostedFile.FileName <> "" Then
End If
End Sub

Simple? I thought so. But when I run the app and click aFile_btn I get the
following error on the "If" line:

Object reference not set to an instance of an object.

You think that's frustrating? there's more. If I copy and paste the exact
code behind the button onto a fresh page, with only a FileUpload control and
a Button, it works perfectly...........

Any ideas?

Paul Shapiro

The online help mentions something about using a file upload control within
an ajax panel. Maybe this helps?
"The FileUpload control is designed to be used only in postback scenarios
and not in asynchronous postback scenarios during partial-page rendering.
When you use a FileUpload control inside an UpdatePanel control, the file
must be uploaded by using a control that is a PostBackTrigger object for the
panel. UpdatePanel controls are used to update selected regions of a page
instead of updating the whole page with a postback. For more information,
see UpdatePanel Control Overview and Partial-Page Rendering Overview."


Hi Paul,

I took your advice and it worked. It wasn't only the update panels; it was
the ScriptManager as well that was causing the problem.
I separated the file upload page and removed the ajax items from it and
all's sane again.

Thanks for your quick response =)

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