Approach to targetting HTTP Handler from Button Click - asp.net

Question

Main purpose here is to target the handler to download a file that is being previewed.
There are two different conditions of the file, one where it is already saved in the database, then the following parameters to the handler through a query string
COIHandler.axd?Action=preview_saved&letterId=xxxx
or
one that hasn't been saved yet, in which i store it in the session and target the handler in the following way
COIHandler.axd?Action=preview_unsaved
then the handler will handle clearing the session after I'm done.
Any thoughts on how to make this occur. Still new to http handlers.
CLARIFICATION
I have a OnClientClick property in my sub classed version of the Button class which allows me to append javascript to it that will be executed client-side. That is where I want the targeting to occur.
I want the user stay on the same page when they click the download button as well.
I dont want to simply do a redirect in javascript that will target the handler and I would like to avoid a pop-up window if possible. Not really sure if that leaves any options

Answer 1

In Response to Yads comment, you can use a button click handler on your page to download the file without a need for a popup or separate HTTP Handler.
protected void btnDownload_OnClick(object sender, EventArgs args)
{
PDFContentData data = GeneratePDFData(); //parses strings from some source (as mentioned in comments)
WebFileUtil.InvokePDFDownload(Page.Context, data);
}
public static class WebFileUtil
{
public static void InvokePDFDownload(HttpContext context, PDFContentData data)
{
context.Response.Clear();
context.Response.ClearContent();
context.Response.ClearHeaders();
FileStore.generateDocument(data, context.Response.OutputStream);
context.Response.ContentType = "application/pdf";
context.Response.ContentEncoding = System.Text.Encoding.UTF8;
context.Response.AddHeader("Content-Disposition", String.Format("attachment;filename={0}_Documenth.pdf", DateTime.Now.ToShortDateString()));
context.Response.End();
}
}

Answer 2

Your handler would actually be .ashx. Other than that your approach seems fine. You can examine the context that is passed into the PrcoessRequest method.
public void ProcessRequest(HttpContext context)
{
switch(context.Request.QueryString["Action"].ToLower())
{
case "preview_saved":
//do stuff for saved
case "preview_unsaved":
//do stuff for unsaved
}
}
UPDATE If you want a central handler, then you'll either want to redirect the user at the end of the call in which case you'll also want to pass a returnUrl parameter in the query string. Then you can just do a context.Response.Redirect(context.Request.QueryString["returnUrl"]). Or if you want the page to retain its state, you're going to have to make an Ajax call to your handler.

Answer 3

First off thank you very much for all the possible solutions they were helpful in getting outside the box.
I figured out a unique solution that I thought I would share.
I place an invisible iframe in the html markup of my page.
then I set a property called OnClientClick in my server control Download Button (this allows me to render a parameter string to the onclick attribute of the html)
I set the property to a javascript method which embodies a recursive algorithm to navigate to the top parent frame of the page, once it reaches that point, I use a simply JQuery selector to look for the iframe I spoke of in step 1. (The reason for the recursion is to maintain support with Master Pages where you will have frames inside of frames).
Set the src attribute of the iframe to the target HTTP Handler. The applied behavior causes the iframe to load the requested source ... but in this case it is a handler, and since it was made all originally from direct user input (via the Download button click), you won't even have the issue of getting the Yellow Bar with IE7+
The handler serves the request and the file is served to the browser
Yay!