pass multidimentional array from ajax to asp.net mvc

Question

hello, I have tried to post json data from angularjs $http post to asp.net mvc controller here is json data example

var postdata =
               {

                  Email: "[email protected]",
                  selectedanswer: {0: 3, 1: 2, 2: 0, 3: 3, 4: 1}
};

angular js code

$http({
                url: "/page/PostFileWithData",
                headers: {
                    'Content-Type': 'application/json; charset=utf-8'
                },
                method: "POST",
                dataType: "json",
                traditional: true,
                data: JSON.stringify(postdata)
            }).success(function (data) {
                console.log(data);
            }).error(function (data) {
                console.log('fail');
            });

controller

public JsonResult PostFileWithData(UserModel userdata)
{
UserModel udata = new UserModel
{
Email = userdata.Email
selectedanswer = userdata.selectedanswer
};
return Json(udata, JsonRequestBehavior.AllowGet);
}

my Modal

public class UserModel
{
public string Email { get; set; }
public string selectedanswer { get; set; }
}

now problem is that I am getting email field ok in console.log but selectedanswer is null

 

like this

 

{Email: "[email protected]", selectedanswer: null}

 

can you please help me at this point?