public ActionResult ShareList(int?Id, string type)
        {
            List <ShareListPM> res = new List <ShareListPM>();

            if (!Id.HasValue)
            {
                return(null);
            }
            if (type == null || type == "")
            {
                return(null);
            }
            if (type.ToLower() == "activiteit")
            {
                Activiteit a = bs.GetActiviteitById((int)Id);
                if (a == null)
                {
                    return(null);
                }
                if (a.Eigenaar.UserName != User.Identity.Name)
                {
                    return(null);
                }
                List <ApplicationUser> userLijst = bs.GetUsers();
                foreach (ApplicationUser user in userLijst)
                {
                    if (user.UserName == User.Identity.Name)
                    {
                        continue;
                    }
                    ShareListPM r = new ShareListPM()
                    {
                        Username = user.UserName,
                        Naam     = user.Voornaam + " " + user.Naam
                    };
                    if (a.DeelLijst.Any(w => w.UserName == user.UserName))
                    {
                        r.IsGedeeld = true;
                    }
                    else
                    {
                        r.IsGedeeld = false;
                    }
                    res.Add(r);
                }
            }
            else if (type.ToLower() == "boek")
            {
                Boek b = bs.GetBoekByID((int)Id);
                if (b == null)
                {
                    return(null);
                }
                if (b.Eigenaar.UserName != User.Identity.Name)
                {
                    return(null);
                }
                List <ApplicationUser> userLijst = bs.GetUsers();
                foreach (ApplicationUser user in userLijst)
                {
                    if (user.UserName == User.Identity.Name)
                    {
                        continue;
                    }
                    ShareListPM r = new ShareListPM()
                    {
                        Username = user.UserName,
                        Naam     = user.Voornaam + " " + user.Naam
                    };
                    if (b.DeelLijst.Any(w => w.UserName == user.UserName))
                    {
                        r.IsGedeeld = true;
                    }
                    else
                    {
                        r.IsGedeeld = false;
                    }
                    res.Add(r);
                }
            }
            else
            {
                return(null);
            }

            return(Json(JsonConvert.SerializeObject(res), JsonRequestBehavior.AllowGet));
        }