从Controller获取Int值到$. ajax

我想从控制器传递int值，并检查它是否大于0在$.ajax。我不知道该怎么做。我试过一个代码，但它给我未定义的值。控制器中的数据工作正常。但是不能返回int值:

AJAX代码:

function bindForm(dialog,urlString) {
    $('form', dialog).submit(function () {
    var data_send = $(this).serializeArray();
    $.ajax({
        url: urlString, 
        type: this.method,
        data: $(this).serialize(),
        success: function (result) {
        alert(result.success);
        if (parseInt(result.success, 10) > 0) {
            alert('Details Added Successfully');
            $('#dialog-form').dialog('close');
            var hdnInvoiceId = document.getElementById("Invoice_Id");
            hdnInvoiceId.value = parseInt(result.success, 10);
            $('#addInvoiceDetail').hide();
            } else {
            alert('Please Re-enter Details');
            bindForm();
            }
        }
    });
    return false;
});

控制器代码:

[HttpPost]
public int AddInvoice(Invoice model)
{
    int Invoice_Id = CRMServiceDL.insertInvoiceDetail(model);
    int success;
    if (Invoice_Id > 0)
    {
        success = Invoice_Id;
    }
        else {
        success = -1;
    }
    return success;
}

[HttpPost]
public JsonResult AddInvoice(Invoice model)
{
    int invoiceId = CRMServiceDL.insertInvoiceDetail(model);
    int success = invoiceId > 0 ? invoiceId : -1;
    return Json(new { success });
}