Question

我只是想在MVC RC中进行一些简单的验证，并且收到错误。出于这个问题的目的，我没有使用UpdateModel 。

以下是表单中的代码：

<%= Html.TextBox("UserId")%>
<%= Html.ValidationMessage("UserId") %>

如果我在控制器中添加以下行，我将在TextBox上得到NullReferenceException：

ModelState.AddModelError("UserId", "*");

所以为了解决这个问题，我还添加了以下内容：

ModelState.SetModelValue("UserId", ValueProvider["UserId"]);

为什么我要重新绑定价值？ 如果我添加错误，我只需要执行此操作，但似乎我不应该这样做。我觉得我做错了什么或者对绑定不够熟悉。

看起来我不是唯一一个看过这个的人。每个请求，这是控制器代码：

[AcceptVerbs(HttpVerbs.Post)]
    public ActionResult Create(FormCollection collection)
    {
        AppUser newUser = new AppUser();

        try
        {
            newUser.UserId = collection["UserId"];

            AppUserDAL.AddUser(newUser);

            return RedirectToAction("Index");
        }
        catch (Exception ex)
        {
            ViewData["ReturnMessage"] = ex.Message;

            ModelState.AddModelError("UserId", "*");
            ModelState.SetModelValue("UserId", ValueProvider["UserId"]);


            return View(newUser);
        }

Answer 1

调用此扩展方法：

        public static void AddModelError (this ModelStateDictionary modelState, string key, string errorMessage, string attemptedValue) {
        modelState.AddModelError (key, errorMessage);
        modelState.SetModelValue (key, new ValueProviderResult (attemptedValue, attemptedValue, null));
    }

来自：Issues with AddModelError() / SetModelValue with MVC RC1

Answer 2

您绝对不需要调用SetModelValue。

也许你只需要你的视图从你传入的模型中拉出文本框？

<%= Html.TextBox("UserId", Model.UserId)%>

我就是这样做的。

Answer 3

您可以尝试使用此扩展来使用lambda表达式设置模型值：

    /// <summary>
    /// Sets model value.
    /// </summary>
    /// <typeparam name="TViewModel">The type of the view model.</typeparam>
    /// <typeparam name="TProperty">The type of the property</typeparam>
    /// <param name="me">Me.</param>
    /// <param name="lambdaExpression">The lambda expression.</param>
    ///<param name="value">New Value</param>
    public static void SetModelValue<TViewModel, TProperty>(
        this ModelStateDictionary me,
        Expression<Func<TViewModel, TProperty>> lambdaExpression,
        object value)
    {

        string key = WebControlsExtensions.GetIdFor<TViewModel, TProperty>(lambdaExpression, ".");

        if (!string.IsNullOrWhiteSpace(key))
        {
            me.SetModelValue(key, new ValueProviderResult(value, String.Empty, System.Globalization.CultureInfo.InvariantCulture));
        }
    }

获取ID：

public static class WebControlsExtensions
{

    /// <summary>
    /// Devuelve el Id correspondiente a la expresión lambda pasada por parámetro reemplazando los caracteres inválidos por la cadena pasada por parámetro
    /// </summary>
    /// <typeparam name="TViewModel">El tipo del modelo</typeparam>
    /// <typeparam name="TProperty">El tipo de la propiedad</typeparam>
    /// <param name="expression">Expresión lambda</param>
    /// <param name="invalidCharReplacement">Cadena de texto que reemplaza a los carácteres inválido</param>
    /// <remarks>
    /// Valid characters consist of letters, numbers, and the hyphen ("-"), underscore ("_"), and colon (":") characters. 
    /// All other characters are considered invalid. Each invalid character in originalId is replaced with the character specified in the HtmlHelper.IdAttributeDotReplacement property.
    /// </remarks>
    /// <returns> Devuelve el Id correspondiente a la expresión lambda</returns>
    public static string GetIdFor<TModel, TProperty>(Expression<Func<TModel, TProperty>> expression, string invalidCharReplacement)
    {
        return TagBuilder.CreateSanitizedId(ExpressionHelper.GetExpressionText(expression), invalidCharReplacement);
    }

}

MVC RC验证：这是对的吗？

3 个答案: