Question

我正在使用ASP.NET MVC4，现在我想添加一个包含来自mysql数据库的数据的下拉列表。这就是我的工作：

在我的视图（Register.cshtml）中：`

<div class="control-group">
    @Html.LabelFor(m => m.DistrictID, new { @class= "control-label"})
    <div class="controls">
        @Html.DropDownListFor(model => model.DistrictID, new SelectList(ViewBag.Districts, "district_id", "district_name", Model.DistrictID))
    </div>
</div>

在我的控制器（AccountController）中：

[AllowAnonymous]
public ActionResult Register()
{
    var districts = repository.GetDistricts();
    ViewBag.Districts = districts;

    return View(new RegisterModel());
}

//
// POST: /Account/Register

[HttpPost]
[AllowAnonymous]
[ValidateAntiForgeryToken]
public ActionResult Register(RegisterModel model)
{

    if (ModelState.IsValid)
    {
        // Attempt to register the User
        try
        {
            MembershipService.CreateUser(model.Name, model.FamilyName, model.BirthDate, model.Sex, model.Nationality, model.Email, model.UserName, model.Password, model.Street, model.StreetNr);

            FormsAuthentication.SetAuthCookie(model.UserName, false);
            return RedirectToAction("Index", "Home");
        }
        catch (ArgumentException ae)
        {
            ModelState.AddModelError("", ae.Message);
        }
    }

    // If we got this far, something failed, redisplay form
    return View(model);
}

我从存储库获取区域，如下所示：

 public IQueryable<district> GetDistricts()
 {
     return from district in entities.districts
            orderby district.district_name
            select district;
 }

我的RegisterModel：

public class RegisterModel
{
    [Required]
    [Display(Name = "Given name")]
    public string Name { get; set; }

    [Required]
    [Display(Name = "Family name")]
    public string FamilyName { get; set; }

    [Required]
    [Display(Name = "Birthdate")]
    public DateTime BirthDate { get; set; }

    [Required]
    [Display(Name = "Sex")]
    public string Sex { get; set; }

    [Required]
    [Display(Name = "Nationality")]
    public string Nationality { get; set; }

    [Required]
    [Display(Name = "Email")]
    public string Email { get; set; }

    [Required]
    [Display(Name = "User name")]
    public string UserName { get; set; }

    [Required]
    [StringLength(100, ErrorMessage = "The {0} must be at least {2} characters long.", MinimumLength = 6)]
    [DataType(DataType.Password)]
    [Display(Name = "Password")]
    public string Password { get; set; }

    [DataType(DataType.Password)]
    [Display(Name = "Confirm password")]
    [Compare("Password", ErrorMessage = "The password and confirmation password do not match.")]
    public string ConfirmPassword { get; set; }

    [Required]
    [Display(Name = "Street")]
    public string Street { get; set; }

    [Required]
    [Display(Name = "Street Number")]
    public int StreetNr { get; set; }

    [Required]
    [Display(Name = "District")]
    public IEnumerable<SelectListItem> Districts { get; set; }

    public int DistrictID { get; set; }
}

下拉列表中有区域，但是当我点击＆＃34;注册＆＃34;我收到这个错误：

值不能为空。   参数名称：items

描述：执行期间发生了未处理的异常   当前的网络请求。请查看堆栈跟踪了解更多信息   有关错误的信息以及它在代码中的起源。

异常详细信息：System.ArgumentNullException：值不能为null。   参数名称：items

当我调试方法时，我发现ModelState无效。
键11是DistrictID，包括districtid但键12是区，并给出错误："The district field is required" ...

我做错了什么？

Answer 1

考虑模型验证失败的情况。对于随请求发送的模型，将再次重新显示视图。不过这一行：

new SelectList(ViewBag.Districts, "district_id", "district_name", Model.Districts)

将null作为第一个参数，因为ViewBag.Districts未重新填充，导致异常。因此，为了避免异常，只需再次设置此属性：

// If we got this far, something failed, redisplay form
var districts = repository.GetDistricts();
ViewBag.Districts = districts;
return View(model);

更新。在查看模型定义时，我们会立即想到Required集合的Districts属性。很可能您不需要用户输入任何这些，也不需要将它们保存到数据库中。尝试删除此属性，有关此属性的错误将消失。

值不能为空。参数名称：items（DrodownList）

1 个答案: