验证在asp.net mvc的一个DropDownList [英] validate a dropdownlist in asp.net mvc

问题描述

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

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

我怎样才能让这个在默认情况下它说： - 选择类别 -

How can I make it so that by default it says "-Select Category-"

和验证检查的东西被选中（客户端和型号）

And validate to check something is selected (client and on the model)

感谢

推荐答案

我简直不敢相信，还有人在ASP.NET MVC 3依然采用的ViewData / ViewBag而不是强类型的视图和视图模型：

I just can't believe that there are people still using ViewData/ViewBag in ASP.NET MVC 3 instead of having strongly typed views and view models:

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

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

和在你的控制器：

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");
    }
}

，然后在你的强类型的视图：

and then in your strongly typed view:

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

此外，如果你想客户端验证不要忘记引用必要的脚本

Also if you want client side validation don't forget to reference the necessary scripts:

<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>

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