ExtJs standard form submit with jsonData for file download - extjs

Question

I'm trying to download a file from WebApi using ExtJs 4.2.3. After reading Extjs 4 downloading a file through ajax call, it looks like my best bet is to use the standard form.submit, however, my data is not passing as expected to the WebApi controller - using the below code, items comes through null.
Controller
public HttpResponseMessage Post(string exportType, List<PcAvailableComponent> items)
{
var dataToExport = _service.ExportItems(exportType, items);
HttpResponseMessage result = new HttpResponseMessage(HttpStatusCode.OK);
var stream = new MemoryStream(dataToExport);
result.Content = new StreamContent(stream);
result.Content.Headers.ContentType =
new MediaTypeHeaderValue("application/octet-stream");
return result;
}
Standard Submit
expForm.submit({
url: AppRootUrl + 'api/AdminDataExport?exportType=' + exportType,
//this doesn't work
jsonData: items,
waitMsg: 'Generating export...',
success: function (form, action) {
if (typeof expWindow !== "undefined") {expWindow.close();}
},
failure: function(form, action) {
Ext.Msg.alert('Failed', 'An error has occurred while generating the export: ' + JSON.parse(action.response.responseText)['ExceptionMessage']);
}
});
Ajax submit (works but can't get file back)
Ext.Ajax.request({
url: AppRootUrl + 'api/AdminDataExport',
params: {
exportType: 'PricingAndCosting'
},
jsonData: items,
method: 'POST',
success: function (response) {
expWindow.close();
console.log("success!");
}
});

Answer 1

Ended up abandoning WebApi for this controller, and just passing the JSON as a string, then deserializing it on the server side:
[HttpPost]
public ActionResult Index(string exportType, string items)
{
var dataToExport = _service.ExportItems(exportType, JsonConvert.DeserializeObject<List<PcAvailableComponent>>(items));
Response.AddHeader("Content-Disposition", "inline; filename=" + exportType + "_" + DateTime.Now.ToString("yyyyMMdd_HHmmss") + ".xlsx");
return File(dataToExport, "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet");
}