public async Task<ActionResult> Create(RegisterViewModel userViewModel, params string[] selectedRoles)
        {
            if (ModelState.IsValid)
            {
                var user = new ApplicationUser { UserName = userViewModel.Email, Email = userViewModel.Email };
                var adminresult = await UserManager.CreateAsync(user, userViewModel.Password);

                //Add User to the selected Roles 
                if (adminresult.Succeeded)
                {
                    if (selectedRoles != null)
                    {
                        var result = await UserManager.AddToRolesAsync(user.Id, selectedRoles);
                        if (!result.Succeeded)
                        {
                            ModelState.AddModelError("", result.Errors.First());
                            ViewBag.RoleId = new SelectList(await RoleManager.Roles.ToListAsync(), "Name", "Name");
                            return View();
                        }
                    }
                }
                else
                {
                    ModelState.AddModelError("", adminresult.Errors.First());
                    ViewBag.RoleId = new SelectList(RoleManager.Roles, "Name", "Name");
                    return View();

                }
                return RedirectToAction("Index");
            }
            ViewBag.RoleId = new SelectList(RoleManager.Roles, "Name", "Name");
            return View();
        }
        public async Task<ActionResult> Register(RegisterViewModel model)
        {
            if (ModelState.IsValid)
            {
                var user = new ApplicationUser { UserName = model.Email, Email = model.Email };
                var result = await UserManager.CreateAsync(user, model.Password);
                if (result.Succeeded)
                {
                    await SignInManager.SignInAsync(user, isPersistent:false, rememberBrowser:false);
                    
                    // 如需如何啟用帳戶確認和密碼重設的詳細資訊,請造訪 http://go.microsoft.com/fwlink/?LinkID=320771
                    // 傳送包含此連結的電子郵件
                    // string code = await UserManager.GenerateEmailConfirmationTokenAsync(user.Id);
                    // var callbackUrl = Url.Action("ConfirmEmail", "Account", new { userId = user.Id, code = code }, protocol: Request.Url.Scheme);
                    // await UserManager.SendEmailAsync(user.Id, "確認您的帳戶", "請按一下此連結確認您的帳戶 <a href=\"" + callbackUrl + "\">這裏</a>");

                    return RedirectToAction("Index", "Home");
                }
                AddErrors(result);
            }

            // 如果執行到這裡,發生某項失敗,則重新顯示表單
            return View(model);
        }