Question

我遇到了一个奇怪的问题....当我使用UpdateModel()或TryUpdateModel()时，一切正常。当我尝试自己绑定时（例如MyObject.FirstName = collection["FirstName"]），我收到"Object reference not set to an instance of an object"错误。

这有点难以解释，所以我将提供代码：

    [HandleError]
    [AcceptVerbs(HttpVerbs.Post)]
    public ActionResult Create(FormCollection collection)
    {
        try
        {
            Model.Event evnt = new Redline.RedlineTimeAttack.Model.Event();

            //When this is uncommented everything works fine.
            //TryUpdateModel<Model.Event>(evnt);

            //this will eventually lead to problems
            evnt.Description = collection["Description"];
            evnt.EndDate = enddate;
            evnt.EventName = collection["EventName"];
            evnt.IsActive = collection["IsActive"].Contains("true");
            evnt.StartDate = startdate;
            evnt.TrackId = trackId;
            evnt.WebContent = collection["WebContent"];


            if (!evnt.IsValid)
            {
              foreach (var error in evnt.GetRuleViolations())
              {
                ModelState.AddModelError(error.PropertyName, error.ErrorMessage);
              } 
            }

            //If there are no validation issues then no problem, redirecttoaction
            //works properly
            if (ModelState.IsValid)
            {
                model.Events.InsertOnSubmit(evnt);
                model.SubmitChanges();
                ViewData["ControlMode"] = "Edit";
                return RedirectToAction("Edit");
            }
            else //returning to View so that user can correct issues causes a null reference error in the view (bombs at first Html.Textbox("ControlName"))
            {
                ViewData["Tracks"] = GetTracks();
                return View("Create", evnt);
            }
        }

这是堆栈跟踪：

System.NullReferenceException was unhandled by user code
Message="Object reference not set to an instance of an object."
Source="System.Web.Mvc"
StackTrace:
   at System.Web.Mvc.HtmlHelper.GetModelStateValue(String key, Type destinationType)
   at System.Web.Mvc.Html.InputExtensions.InputHelper(HtmlHelper htmlHelper, InputType inputType, String name, Object value, Boolean useViewData, Boolean isChecked, Boolean setId, Boolean isExplicitValue, IDictionary`2 htmlAttributes)
   at System.Web.Mvc.Html.InputExtensions.TextBox(HtmlHelper htmlHelper, String name, Object value, IDictionary`2 htmlAttributes)
   at System.Web.Mvc.Html.InputExtensions.TextBox(HtmlHelper htmlHelper, String name)
   at ASP.views_event_create_aspx.__RenderContent2(HtmlTextWriter __w, Control parameterContainer) in d:\TFSProjects\Redline Time Attack\Main\Source\Redline.RedlineTimeAttack.Web\Views\Event\Create.aspx:line 18
   at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
   at System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
   at System.Web.UI.Control.Render(HtmlTextWriter writer)
   at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
   at ASP.views_shared_site_master.__Render__control1(HtmlTextWriter __w, Control parameterContainer) in d:\TFSProjects\Redline Time Attack\Main\Source\Redline.RedlineTimeAttack.Web\Views\Shared\Site.Master:line 29
   at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
   at System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
   at System.Web.UI.Control.Render(HtmlTextWriter writer)
   at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
   at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter writer, ICollection children)
   at System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
   at System.Web.UI.Page.Render(HtmlTextWriter writer)
   at System.Web.Mvc.ViewPage.Render(HtmlTextWriter writer)
   at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter adapter)
   at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
InnerException:

Answer 1

我在这里找到了一些见解：http://forums.asp.net/p/1396019/3006051.aspx

如果您不想使用内置模型   绑定，然后使用Bultin验证   （SanjaySutar想要使用），适合每一个人   您需要添加ModelError   添加ModelValue：   ModelState.AddModelError（“Name”，“Bad   名“）;

ModelState.SetModelValue（ “姓名”，   ValueProvider [ “名称”]）;

所以我更新了我的代码：

ModelState.SetModelValue("Description", new ValueProviderResult(ValueProvider["Description"].AttemptedValue, collection["Description"], System.Globalization.CultureInfo.CurrentCulture));
ModelState.SetModelValue("EventName", new ValueProviderResult(ValueProvider["EventName"].AttemptedValue, collection["EventName"], System.Globalization.CultureInfo.CurrentCulture));
ModelState.SetModelValue("EndDate", new ValueProviderResult(ValueProvider["EndDate"].AttemptedValue, collection["EndDate"], System.Globalization.CultureInfo.CurrentCulture));
ModelState.SetModelValue("StartDate", new ValueProviderResult(ValueProvider["StartDate"].AttemptedValue, collection["StartDate"], System.Globalization.CultureInfo.CurrentCulture));
ModelState.SetModelValue("TrackId", new ValueProviderResult(ValueProvider["TrackId"].AttemptedValue, collection["TrackId"], System.Globalization.CultureInfo.CurrentCulture));
ModelState.SetModelValue("WebContent", new ValueProviderResult(ValueProvider["WebContent"].AttemptedValue, collection["WebContent"], System.Globalization.CultureInfo.CurrentCulture));

我这样做的原因是因为我想要一个。在我的业务对象中完成所有（或尽可能多）验证，包括必填字段和b。我想在验证摘要中使用我自己的消息（例如“FieldX是必填字段。”而不是“需要值。”）。如果有更好的方法，请参阅我的另一个问题：ASP.NET MVC - Custom validation message for value types

Answer 2

enddate，startdate和trackId来自哪里？这甚至不应该编译，但也许我只是愚蠢而没有看到他们的声明。我确定它只是看不到的地方，对吧？

确保所有这些表单值实际上也包含其中的内容。

ASP.NET MVC - Html.Textbox（）抛出“对象引用未设置为对象的实例”

2 个答案: