C# web-api post to function with two parameters

Question

I am trying to post two parameters to the following function but I dont manage to reach the function:

public void SetShopSubCategories([FromBody]string userId, int []subCategories )
{

}

This is how I post:

var subCategories = [ 1, 2, 3, 4, 5];
var userId = "123";

            $.ajax({
                type: "POST",
                url: "/Category/SetShopSubCategories/",
                contentType: 'application/json; charset=utf-8',
                data: JSON.stringify(userId, subCategories),
                success: function () {
                    alert("OK");
                },
                error: function () {
                    alert("error");
                }

When I post only with one parameter it goes well and I can reach the function:

public void SetShopSubCategories([FromBody]string userId )
{

}

var userId = "123";

        $.ajax({
            type: "POST",
            url: "/Category/SetShopSubCategories/",
            contentType: 'application/json; charset=utf-8',
            data: JSON.stringify(userId, subCategories),
            success: function () {
                alert("OK");
            },
            error: function () {
                alert("error");
            }

This one also goes well:

public void SetShopSubCategories( int []subCategories )
{

}

var subCategories = [ 1, 2, 3, 4, 5]; 

            $.ajax({
                type: "POST",
                url: "/Category/SetShopSubCategories/",
                contentType: 'application/json; charset=utf-8',
                data: JSON.stringify(subCategories),
                success: function () {
                    alert("OK");
                },
                error: function () {
                    alert("error");
                }

My RoutConfig:

 routes.IgnoreRoute("{resource}.axd/{*pathInfo}");


            GlobalConfiguration.Configuration.Routes.MapHttpRoute(
                name: "SetCategories",
                routeTemplate: "{controller}/{action}"
            );


            routes.MapRoute(
                name: "Default",
                url: "{controller}/{action}/{id}",
                defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
            );

Answer 1

Model

public class Mymodel
    {
        public string UserId { get; set; }        
        public int[] subCategories { get; set; }
    }

Controller Action

[HttpPost]
        public void SetShopSubCategories([FromBody]Mymodel model)
        {

        }

Ajax Call:

var subCategories = [1, 2, 3, 4, 5];
var userId = "123"
$.ajax({
    type: "POST",
    url: "/api/Values",
    contentType: "application/json; charset=utf-8",  
    data: JSON.stringify({ userid: userId, subCategories: subCategories }),
    success: function () {
        alert("OK");
    },
    error: function () {
        alert("error");
    }
});

Here is the link : http://www.asp.net/web-api/overview/formats-and-model-binding/parameter-binding-in-aspnet-web-api

you will find that multiple parameter not allowed or problematic due to type of stream.