File download of server -generated file from button asp.net mvc - asp.net-mvc

Question

OK, this sounds dumb even to me, but I am clearly having a "bad brain day" and need help.
On a button click, I want to generate a file based on parameters taken from 2 ViewData fields and a checkbox control, and have the file be downloaded/displayed, just as you get with a fixed link.
Most of it is going fine, the controller method passes back a file like so: Return File(filePath, "text/csv") - but then what? How do I connect that to the button and have the file download/open dialog come up?
I feel I am missing something really simple. Just calling the controller via ajax seems to do nothing... the code is called but I see no results
***** EDIT: ******
The following gets me a file automatically downloaded, but with the name "download" - I want to offer the user the choice to open or download, and to set the filename - how do I do that?
serialize = function (obj) {
var str = [];
for (var p in obj)
if (obj.hasOwnProperty(p)) {
str.push(encodeURIComponent(p) + "=" + encodeURIComponent(obj[p]));
}
return str.join("&");
};
var params = {
ID1: '#ViewData("ID1")',
ID2: '#ViewData("ID2")',
flag: getFlag()
};
var actionUrl = ('#Url.Action("ProduceReport", "Report")');
actionUrl += "/?" + serialize(params);
window.open(actionUrl);
* 2nd edit *
Controller code - this produces a file and returns the path. After the call to ProduceReport The file is there on that path, this I have checked. It is used in production to email the file (works fine).
public FileResult ProduceReport(int ID1, int ID2, bool flag = false)
{
var filePath = ExcelReports.ProduceReportExcel(Models.UserInfo.GetCurrentUserID, ID1, ID2, flag);
return File(filePath,"application/vnd.ms-excel");
}

Answer 1

The acceptable compromise that I found, to at least get the file downloaded. I will have to do further research to see if I can print it automatically.
Javascript:
serialize = function (obj) {
var str = [];
for (var p in obj)
if (obj.hasOwnProperty(p)) {
str.push(encodeURIComponent(p) + "=" + encodeURIComponent(obj[p]));
}
return str.join("&");
};
var params = {
ID1: '#ViewData("ID1")',
ID2: '#ViewData("ID2")',
flag: getFlag()
};
var actionUrl = ('#Url.Action("ProduceReport", "Report")');
actionUrl += "/?" + serialize(params);
window.location.href = actionUrl;
Controller: Note 3rd parameter on the File() call
public FileResult ProduceReport(int ID1, int ID2, bool flag = false)
{
var filePath = ExcelReports.ProduceReportExcel(Models.UserInfo.GetCurrentUserID, ID1, ID2, flag);
return File(filePath,"application/vnd.ms-excel",System.IO.Path.GetFileName(filePath));
}