public ActionResult SaveNewDocument(FormCollection f)
        {
            string email = f["txtNew_email"].ToString();

            if (ModelState.IsValid)
            {
                try
                {
                    DangKyNhanThongBao dk = new DangKyNhanThongBao();
                    dk.email      = email;
                    dk.ngaydangky = DateTime.Now;
                    db.DangKyNhanThongBao.Add(dk);
                    db.SaveChanges();
                }
                catch (Exception e)
                {
                    ViewData["EditError"] = e.Message;
                }
            }
            else
            {
                ViewData["EditError"] = "Please, correct all errors.";
            }
            return(RedirectToAction("Index", "QuanLyEmailDangKy"));
        }
        //-------------------------------------- Đăng ký nhận tin
        public ActionResult DangKyNhanTin(FormCollection f)
        {
            string txtEmail = f["txtEmail"].ToString();
            var    model    = db.DangKyNhanThongBao;

            if (ModelState.IsValid)
            {
                try
                {
                    var x = db.DangKyNhanThongBao.Where(n => n.email == txtEmail);
                    if (x.Count() == 0)
                    {
                        DangKyNhanThongBao dknt = new DangKyNhanThongBao();
                        dknt.email      = txtEmail;
                        dknt.ngaydangky = DateTime.Now;
                        db.DangKyNhanThongBao.Add(dknt);
                        db.SaveChanges();
                        ViewBagData();
                        ViewBag.KetQua = "Đăng ký nhận tin thành công!";
                        return(View("Index"));
                    }
                    else
                    {
                        ViewBagData();
                        ViewBag.KetQua = "Email đã được đăng ký trước đó!";
                        return(View("Index"));
                    }
                }
                catch (Exception e)
                {
                    ViewData["EditError"] = e.Message;
                }
            }
            else
            {
                ViewData["EditError"] = "Please, correct all errors.";
            }
            return(null);
        }