asp.net-mvc – 如何在验证集合中添加验证错误asp.net mvc？

在我的控制器的动作中，我有以下代码：

public ActionResult GridAction(string id)
{
    if (String.IsNullOrEmpty(id)) 
    {
        // add errors to the errors collection and then return the view saying that you cannot select the dropdownlist value with the "Please Select" option
    }

    return View(); 
}

更新：

if (String.IsNullOrEmpty(id))
{
    // add error 
    ModelState.AddModelError("GridActionDropDownList","Please select an option");
    return RedirectToAction("Orders"); 
}

更新2：

这是我更新的代码：

@Html.DropDownListFor(x => x.SelectedGridAction,Model.GridActions,"Please Select") 
@Html.ValidationMessageFor(x => x.SelectedGridAction)

该模型如下所示：

public class MyInvoicesViewModel
{

    private List<SelectListItem> _gridActions;

    public int CurrentGridAction { get; set; }

    [Required(ErrorMessage = "Please select an option")]
    public string SelectedGridAction { get; set; }

    public List<SelectListItem> GridActions
    {
        get
        {
            _gridActions = new List<SelectListItem>();
            _gridActions.Add(new SelectListItem() { Text = "Export to Excel",Value = "1" });

            return _gridActions;
        }
    }
}

这里是我的控制器动作：

public ActionResult GridAction(string id)
{
    if (String.IsNullOrEmpty(id))
    {
        // add error 
        ModelState.AddModelError("SelectedGridAction","Please select an option");
        return RedirectToAction("Orders"); 
    }

    return View(); 
}

什么都没发生！我完全迷失在这一个！

更新3：

我现在使用以下代码，但仍然验证不会触发：

public ActionResult GridAction(string id)
{
    var myViewModel= new MyViewModel();
    myViewModel.SelectedGridAction = id; // id is passed as null           

    if (!ModelState.IsValid)
    {
        return View("Orders");
    }

更新4：

$("#linkGridAction").click(function () {
    alert('link grid action clicked'); 

    $.get('GridAction/',{ SelectedGridAction: $("#SelectedGridAction").val() },function (result) {
        alert('success');
    });
});

控制器如下所示：

// OrderViewModel has a property called SelectedGridAction. 
public ActionResult GridAction(OrderViewModel orderViewModel)
{
    return View(); 
}

更新5：验证没有触发：

public ActionResult GridAction(OrderViewModel orderViewModel)
{
    if (!ModelState.IsValid)
    {
        return View("Orders",orderViewModel); 
    }
    return View(); 
}

解决方法

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

接着：

public ActionResult GridAction(MyViewModel model)
{
    if (ModelState.IsValid)
    {
        // the model is valid,the user has selected an id => use it
        return RedirectToAction("Success");
    }
    return View();
}

更新：

在对我的答复的数百条评论之后，我觉得有必要提供一个充分的工作实例：

像往常一样，从视图模型开始：

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

    public IEnumerable<SelectListItem> Items 
    {
        get
        {
            // Dummy data
            return new SelectList(Enumerable.Range(1,10)
                .Select(i => new SelectListItem 
                {
                    Value = i.ToString(),Text = "item " + i 
                }),"Value","Text");
        }
    }
}

然后一个控制器：

public class HomeController: Controller
{
    public ActionResult Index()
    {
        return View(new MyViewModel());
    }

    [HttpPost]
    public ActionResult Index(MyViewModel model)
    {
        if (!ModelState.IsValid)
        {
            // The user didn't select any value => redisplay the form
            return View(model);
        }
        // TODO: do something with model.SelectedItemId
        return RedirectToAction("Success");
    }
}

最后的看法：

<% using (Html.BeginForm()) { %>
    <%= Html.DropDownListFor(
        x => x.SelectedItemId,Model.Items,"-- Select Item --"
    ) %>
    <%= Html.ValidationMessageFor(x => x.SelectedItemId) %>
    <input type="submit" value="OK" />
<% } %>

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