Is response to Ajax call different from that of to full postback - asp.net

Question

When I try the following code with a postback the file download takes place normally:
FileInfo file = new FileInfo("C:\\a.txt");
Response.ClearContent();
Response.AddHeader("Content-Disposition", "attachment; filename=" + file.Name);
Response.AddHeader("Content-Length", file.Length.ToString());
Response.ContentType = "text/plain";
Response.TransmitFile(file.FullName);
Response.End();
However if I put the above code inside a public static web method and call it with AJAX I get error, like "Process was being aborted".(Of course to get the current response I write HttpContext.Current.Response) This makes me think that the nature of the two responses are different. My question is if they are different, then what exactly is/are different? Is there a way to achieve the same thing with AJAX?

Answer 1

The browser isn't going to receive the file via an XHR (Ajax) call. You will want to return the file location and then send the browser to that file via window.location or window.open.
Edit: Here's a Web Forms sample. My Web Forms skills are a little rusty since I've been using MVC now; the syntax is off the top of my head so you might need to fix it up a little.
ASPX Page
<div id="whateverIsContainingYourDialog">
<form id="mikeJMIsAwesome" runat="server">
<asp:TextBox id="firstName" runat="server" />
<asp:TextBox id="lastName" runat="server" />
<asp:Button id="submit" runat="server" />
</form>
</div>
Server Side Code
protected void submit_OnClick(object sender, EventArgs e) {
//Your logic for creating the file and the code you originally posted for serving the file.
}

Answer 2

What Ek0nomik said, file downloads are handled by the browser and cannot be handled through Javascript. The responses are both identical they are are both just http responses - you can verify this with fiddler or another tool (http://www.fiddler2.com/fiddler2/).
Essentially you ajax method will not be able to handle receiving a file and will certainly not have the permissions to assemble it and store it on you hard drive.
You can 'fake' a user clicking on a link using some Javascript.
Please check this similar question for an answer. I've pasted the answer from it below.
starting file download with JavaScript
We do it that way: First add this script.
<script type="text/javascript">
function populateIframe(id,path)
{
var ifrm = document.getElementById(id);
ifrm.src = "download.php?path="+path;
}
</script>
Place this where you want the download button(here we use just a link):
<iframe id="frame1" style="display:none"></iframe>
download
The file 'download.php' (needs to be put on your server) simply contains:
<?php
header("Content-Type: application/octet-stream");
header("Content-Disposition: attachment; filename=".$_GET['path']);
readfile($_GET['path']);
?>
So when you click the link, the hidden iframe then gets/opens the sourcefile 'download.php'. With the path as get parameter. We think this is the best solution!