验证asp.net mvc中的下拉列表

Question

//in controller
ViewBag.Categories = categoryRepository.GetAllCategories().ToList();

//in view
 @Html.DropDownList("Cat", new SelectList(ViewBag.Categories,"ID", "CategoryName"))

如何制作它以便默认情况下显示"-Select Category-"

并验证检查选择的内容(客户端和模型)

谢谢

Answer 1

我简直无法相信有人仍然在ASP.NET MVC 3中使用ViewData/ViewBag而不是强类型视图和视图模型:

public class MyViewModel
{
    [Required]
    public string CategoryId { get; set; }

    public IEnumerable<Category> Categories { get; set; }
}

并在您的控制器中:

public class HomeController: Controller
{
    public ActionResult Index()
    {
        var model = new MyViewModel
        {
            Categories = Repository.GetCategories()
        }
        return View(model);
    }

    [HttpPost]
    public ActionResult Index(MyViewModel model)
    {
        if (!ModelState.IsValid)
        {
            // there was a validation error =>
            // rebind categories and redisplay view
            model.Categories = Repository.GetCategories();
            return View(model);
        }
        // At this stage the model is OK => do something with the selected category
        return RedirectToAction("Success");
    }
}

然后在你的强类型视图中:

@Html.DropDownListFor(
    x => x.CategoryId, 
    new SelectList(Model.Categories, "ID", "CategoryName"), 
    "-- Please select a category --"
)
@Html.ValidationMessageFor(x => x.CategoryId)

此外,如果您想要客户端验证,请不要忘记引用必要的脚本:

<script src="@Url.Content("~/Scripts/jquery.validate.js")" type="text/javascript"></script>
<script src="@Url.Content("~/Scripts/jquery.validate.unobtrusive.js")" type="text/javascript"></script>

Answer 2

有一个带有3个参数的重载.Html.DropdownList(name, selectList, optionLabel) 更新:下面的代码片段中有一个拼写错误.

@Html.DropDownList("Cat", new SelectList(ViewBag.Categories,"ID", "CategoryName"), "-Select Category-")

用于验证器使用

@Html.ValidationMessage("Cat")