append an array to 'formdata' and how to get server side?

I'm using FormData to upload files. I also want to send an array of other data.

When I send just the image, it works fine. When I append some text to the formdata, it works fine. When I try to attach the 'ProIList' array below, everything else works fine but no array is sent

this is my angular.js file code :

this.AddPro = function (file, P) {
var formData = new FormData();
formData.append("file", file);
formData.append("name", P.name);
formData.append("description", P.description);
formData.append("ProIList", P.ProIList);  // this is array list      

var Response = $http.post("/Product/AddProduct", formData,
    {
        transformRequest: angular.identity,
        headers: { 'Content-Type': undefined }
    })
.success(function (res) {
    Response = res;
})
.error(function () {
});
return Response;
}

this is my controller method :

[HttpPost]
[Route("AddProduct")]
public string AddProduct(string name, string description, IList<ProductItems> ProIList) // here i m not getting array 
{
    Products objP = new Products();            
    string Res = "";

                objP.name = name;
                objP.description = description;                       
                db.Promotions.Add(objP); // and here add product is done now want to add ProductItems table entry so how can do 
               db.SaveChanges();                  
    return Res;
}

this is my entity productItmes :

 [Table("ProductItems ")]
  public class ProductItems 
  {
  [Key]
  public int id { get; set; }

[ForeignKey("Products")]
public int pid {get; set;}

public int Qty { get; set; }

public Decimal Rate { get; set; }

public virtual Products Products { get; set; }
}