Best way to return dynamic non-html content from a page

Question

I should start by saying that I am using ASP.NET using C# in a .NET 2.0 environment. In particular, I am trying to generate a csv download when the user clicks on a link button. The link to my postback is inside an UpdatePanel. In the past (before ajax) to return non-html content I would use code such as the following:

string filename = e.CommandArgument.ToString();//somefile.csv
string fileContents = SomeClass.GetFile(filename);

Response.AddHeader("Content-disposition", 
                   string.Format("attachment; filename={0}", filename));
Response.Write(fileContents);

But since the content is not trying to do a full refresh of the browser this technique does not work.

Does someone have a better approach for this kind of situation. One constraint I have is that I am stuck with .net 2.0 for this part of the project and can't switch to 3.5 to solve this problem.

p.s. I need to generate the content with a dynamic filename as well

Answer 1

I would avoid generating a postback for this at all. Istead, you want to use a completely separate page, preferably even just a handler (*.ashx). Then you can use a normal hyperlink and your old attachment code will work just fine.

Answer 2

Create a server-side container (even an HTML DIV with runat="server") inside the UpdatePanel, and set the .InnerHtml or .InnerText property to the fileContents variable when the UpdatePanel is refreshed.

Answer 3

This is some anonymized code I'm using to generate a CSV download from an multi dimensional array.

Response.Clear();
Response.ClearHeaders();
Response.ContentType = "application/vnd.ms-excel";
String shippingFileName = "filename.csv";
Response.AddHeader( "Content-Disposition", "attachment; filename=" + shippingFileName );
String[] row = { "Head1", "Head2" .... };
Response.Write( arrayToCSVString( row ) ); // quotes commas, and other formatting niceties

foreach (row in arrayOfRows) Response.Write( arrayToCSVString( row ) );
Response.Flush();

Answer 4

I think the answer is to make sure that LinkButton performs a synchronous operation. I think Joel's answer is better, but something like this should work for post backs.

Make sure the UpdatePanel's UpdateMode is set to "Conditional" and add a trigger to the Update Panel

<asp:UpdatePanel ... UpdateMode="Conditional">
    <ContentTemplate>...</ContentTemplate>
    <Triggers>
        <asp:PostBackTrigger ControlID="CsvLinkButton" />
    </Triggers>
</asp:UpdatePanel>