File Upload Question

Ron Howerton · October 20th, 2006, 03:22 PM

I have an ASP.NET application that generates HTML code. By this, I mean that the code uses write.response to write HTML code directly to the browser for the entire page:

Reponse.Write("<HTML lang=""en"" METHOD=""POST"" ENCTYPE=""multipart/form-data"">")

This is a problem, because I need to enable the generated form to upload files to a folder on the server. I'm not sure about this, but it seems unlikely to me that I can generate ASP.NET fileupload controls to do this because they are translated to input type="file" before delivery to the browser. If I'm wrong about that, please let me know, but for now I'm assuming that I must use the old way:

Response.Write("<input type=""file"" name=""filAttachment"" size=30> ")

This works OK to find the file to be uploaded and, in fact, that's pretty much what I see in the browser source code when asp:fileupload is translated.

But I seem to be missing the reference to whatever sits on the server to save the file when the form is submitted. .NET allows you to reference the upload control directly in VB and it's as simple as using the .SAVEAS method:

filAttachment.PostedFile.SaveAs...

But of course, I'd get a compiler error trying to reference a field that's defined in generated HTML but not on the .NET form itself because VS doesn't know it exists without the form definition. I could put an asp:fileupload object on the .NET page before adding my generated HTML code, but then I'd be limited to however many such fields I put there, and users always want more. So, I'd rather not go that route if I can help it.

Has anybody got an example of the server side code needed to save uploaded files or an alternative suggestion on how to accomplish this?

Imar · October 21st, 2006, 03:30 AM

Hi Ron,

The problem with your method (e.g. outputting HTML for the upload controls) is that they end up as simple HTML client controls, with no server side counterpart.

What you could do is create true server side Upload controls and add them to the page.

Something like this:

Code:

Dim myUpload As FileUpload = New FileUpload()
myUpload.ID = "FileUpload1"
myPlaceholder.Controls.Add(myUpload)

myUpload = New FileUpload()
myUpload.ID = "FileUpload2"
myPlaceholder.Controls.Add(myUpload)

myUpload = New FileUpload()
myUpload.ID = "FileUpload3"
myPlaceholder.Controls.Add(myUpload)

This adds three FileUpload controls to a PlaceHolder control.

Then at post back, you can do something like this:

Code:

Dim myUpload As FileUpload = CType(Page.FindControl("FileUpload1"), FileUpload)
' Do something with the first file here.
myUpload = CType(Page.FindControl("FileUpload2"), FileUpload)
' Do something with the second file here etc

You should create the controls in the Page_Init event handler so they are available and filled by the time you need them.

For more info:

http://support.microsoft.com/default.aspx/kb/317515

or search Google for create controls dynamically.

Hope this helps,

Imar

---------------------------------------
Imar Spaanjaars
Everyone is unique, except for me.
Author of ASP.NET 2.0 Instant Results and Beginning Dreamweaver MX / MX 2004
Want to be my colleague? Then check out this post.

Ron Howerton · October 23rd, 2006, 08:42 AM

Hi Imar,

Thanks for your response. I've unfortunately just discovered I posted my question in the wrong forum. The application runs in 1.1, not 2.0, and your suggested solution doesn't appear to work there. At least, I can't seem to reference the FileUpload object there, anyway.

I've reposted my question to the 1.1 beginners forum instead. Sorry for the confusion.

Imar · October 23rd, 2006, 01:06 PM

Hi Ron,

In ASP.NET 2, the new WebControl FileUpload was introduced. For .NET 1.x, you can use the HtmlControl HtmlInputFile. So something like this should work (copied from a working application):

Code:

private void CreateUploadControls()
{
  maxImageControls = 5;  
  for (int i = 0; i < maxImageControls; i++)
  {
    HtmlInputFile myControl = new HtmlInputFile();
    myControl.ID = "FileUpload" + i.ToString();
    myControl.Style.Add("width" , "300px");
    myControl.Attributes.Add("class", "MyClass");
    plcUploads.Controls.Add(myControl);
    plcUploads.Controls.Add(new LiteralControl("<br /><br />"));
  }
}

This code adds five upload controls; each separated by two line breaks.

Hope this helps,

Imar
---------------------------------------
Imar Spaanjaars
Everyone is unique, except for me.
Author of ASP.NET 2.0 Instant Results and Beginning Dreamweaver MX / MX 2004
Want to be my colleague? Then check out this post.