public IActionResult Edit(int id, User user)
        {
            if (user != null && id == user.Id && _users.ContainsKey(id) && ModelState.IsValid)
            {
                _users[id] = user;
                return RedirectToAction("Index");
            }

            ViewBag.Items = _items;
            return View();
        }
        public IActionResult Create(User user)
        {
            if (user != null && ModelState.IsValid)
            {
                var id = _next++;
                user.Id = id;
                _users[id] = user;
                return RedirectToAction("Index");
            }

            ViewBag.Items = _items;
            return View();
        }