Question

在我网站的某个页面上，某人可以更改现有用户的用户级别。

下拉列表的数据来自名为AspNetRoles的表。所选数据应保存到AspNetUserRoles

但由于某种原因，我得到一个NULL exeption错误代码：

控制器：

 public ActionResult UserEdit(string Id)
            {
                var SelectedRoles = from r in db.AspNetRoles
                                    where r.Id == r.Id
                                    orderby r.Id
                                    select new { r.Id, Value = r.Name };
                ViewBag.SelectedRoles = new SelectList(SelectedRoles.Distinct(), "Id", "Value");
                if (Id == null)
                {
                    return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
                }
                AspNetUserRoles aspNetUser = db.AspNetUserRoles.Find(Id);
                if (aspNetUser == null)
                {
                    return HttpNotFound();
                }
                return View(aspNetUser);
            }

            [HttpPost]
            [ValidateAntiForgeryToken]
            public ActionResult UserEdit([Bind(Include = "UserId,RoleId")] AspNetUserRoles aspNetUserRoles,  FormCollection formCollection)
            {
               aspNetUserRoles.RoleId = (formCollection["SelectedRoles"]);
                //ManageMessageId? message;

                if (ModelState.IsValid)
                {
                    db.Entry(aspNetUserRoles).State = EntityState.Modified;
                    db.SaveChanges();
                    TempData["AlertMessage"] = "User Edited Successfully";
                    return RedirectToAction("ManageAccounts");
                }
                return View(aspNetUserRoles);
            }

查看：

<div class="form-horizontal">
    <h4>AspNetUserRoles</h4>
    <hr />
    @Html.ValidationSummary(true, "", new { @class = "text-danger" })
    @Html.HiddenFor(model => model.UserId)
    @Html.HiddenFor(model => model.RoleId)

    <div class="form-group">
        @Html.Label("Email", htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.EditorFor(model => model.AspNetUsers.Email, new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.AspNetUsers.Email, "", new { @class = "text-danger" })
        </div>
    </div>
    <div class="form-group">
        @Html.Label("Email bevestigd", htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.CheckBoxFor(model => model.AspNetUsers.EmailConfirmed, new { htmlAttributes = new { @class = "form-control" } })
            @Html.ValidationMessageFor(model => model.AspNetUsers.EmailConfirmed, "", new { @class = "text-danger" })
        </div>
    </div>
    <div class="form-group">
        @Html.Label("Rechten", htmlAttributes: new { @class = "control-label col-md-2" })
        <div class="col-md-10">
            @Html.DropDownListFor(m =>m.RoleId, (IEnumerable<SelectListItem>)ViewBag.SelectedRoles, new { @class = "form-control" })
         @*   @Html.DropDownList("SelectedRoles", null, new { @class = "form-control" })*@
            @Html.ValidationMessageFor(model => model.AspNetRoles.Name, "", new { @class = "text-danger" })
        </div>
    </div>

    <div class="form-group">
        <div class="col-md-offset-2 col-md-10">
            <input type="submit" value="Save" class="btn btn-primary" />
        </div>
    </div>
</div>
<div>
    <button onclick="location.href='@Url.Action("ManageAccounts", "Manage")';return false; " class="btn btn-primary">Back to list</button>
</div>

}

我希望你能帮助我。如果需要更多信息，我很乐意分享这些信息

Answer 1

在Controller中尝试：

var SelectedRoles = from r in db.AspNetRoles
                         where r.Id == r.Id
                         orderby r.Id
                         select new { r.Id, r.Name };

ViewBag.SelectedRoles = new SelectList(SelectedRoles, "Id", "Name");

在视图中：

@Html.DropDownListFor(model => model.RoleId, ViewBag.SelectedRoles as SelectListItem))

C＃MVC中的下拉列表返回null

1 个答案: