Passing parameters in ajax call - asp.net

Question

I'm trying to make an ajax call to the controller method. without parameter it works fine. Once i add the parameter i always receive a null parameter to the cotroller. I think i have correctly done the parameter passing in ajax call.
<script type="text/javascript">
$(document).ready(function () {
$('#lstStock').change(function () {
var serviceURL = '<%= Url.Action("GetStockPrice", "Delivery") %>';
var dropDownID = $('select[id="lstStock"] option:selected').val();
alert(dropDownID); // here i get the correct selected ID
$.ajax({
type: "POST",
url: serviceURL,
data: '{"stockID":"' + dropDownID + '"}',
contentType: "application/json; charset=utf-8",
dataType: "json",
success: successFunc,
error: errorFunc
});
function successFunc(data, status) {
alert(data.Result);
}
function errorFunc() {
alert('error');
}
})
});
</script>
Controller:
[HttpGet]
public ActionResult GetStockPrice()
{
return View();
}
[HttpPost]
[ActionName("GetStockPrice")]
public ActionResult GetStockPrice1(string stockID)//I get the null parameter here
{
DeliveryRepository rep = new DeliveryRepository();
var value = rep.GetStockPrice(stockID);
return Json(new { Result = value }, JsonRequestBehavior.AllowGet);
}

Answer 1

It's because you are treating the data as a string
data: '{"stockID":"' + dropDownID + '"}',
you can change it to:
data: { stockID: dropDownID },
in some cases, depending on the parameter declared in your controller method, you need to serialize the data. If you need to do that then this is how you would do it:
var o = { argName: some_value };
$.ajax({
// some other config goes here
data: JSON.stringify(o),
});

Answer 2

try data: { stockID : dropDownID},
$('#lstStock').change(function () {
var serviceURL = '<%= Url.Action("GetStockPrice", "Delivery") %>';
var dropDownID = $('select[id="lstStock"] option:selected').val();
// $(this).val(); is better
alert(dropDownID); // here i get the correct selected ID
$.ajax({
type: "POST",
url: serviceURL,
data: { stockID : dropDownID},
....

Answer 3

Try specifying:
data: { stockID : dropDownID },
It looks like you're passing up "stockID" not stockID.
A good tool to use for this is Fiddler, it will allow you to see if the Controller action is hit and what data was sent upto the server.