Controller怎么接收Ajax传来的data

var json = { "VendorId": strVendorId, "VendorName": strVendorName, "Remark": strRemark, "PurchaseOrderId": strPurchaseOrderId, "MatId":strMatId, "decThisTimeQty": decThisTimeQty };

$.ajax({
type: "POST",
url: "/PurchaseOrder/Add",
data: JSON.stringify(json),
dataType: "json",

success: function (data) { //回调函数，data为形参，是从login-cl.php页面返回的值
if (data.trim() == "OK") //trim()去空格
alert("添加成功");
else
alert("添加失败");
}
});

public bool Add()
{
var sr = new StreamReader(Request.InputStream);
string stream = sr.ReadToEnd();
JavaScriptSerializer js = new JavaScriptSerializer();
var mian = js.Deserialize<DeliveryOrder>(stream);
var detail = js.Deserialize<DeliveryOrderDetail>(stream);

}