asp.net-mvc – ASP.NET MVC – Html.Textbox()throws“对象引用

发布时间：2020-12-15 23:26:37 所属栏目：asp.Net 来源：网络整理

导读：我遇到一个奇怪的问题….当我使用UpdateModel()或TryUpdateModel(),一切正常.当我尝试绑定自己(例如MyObject.FirstName = collection [“FirstName”])时,我得到一个“对象引用未设置为对象的实例”错误. 这有点难以解释,所以我将介绍代码： [HandleError] [

我遇到一个奇怪的问题….当我使用UpdateModel()或TryUpdateModel(),一切正常.当我尝试绑定自己(例如MyObject.FirstName = collection [“FirstName”])时,我得到一个“对象引用未设置为对象的实例”错误.

这有点难以解释,所以我将介绍代码：

[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)
   at ASP.views_event_create_aspx.__RenderContent2(HtmlTextWriter __w,Control parameterContainer) in d:TFSProjectsRedline Time AttackMainSourceRedline.RedlineTimeAttack.WebViewsEventCreate.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:TFSProjectsRedline Time AttackMainSourceRedline.RedlineTimeAttack.WebViewsSharedSite.Master:line 29
   at System.Web.UI.Control.RenderChildrenInternal(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)
   at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint,Boolean includeStagesAfterAsyncPoint)
InnerException:

解决方法

我在这里找到了一些洞察力： http://forums.asp.net/p/1396019/3006051.aspx

If you don’t want to use Builtin Model
Binding,then to use Bultin Validation
(SanjaySutar want to use),for every
ModelError you add,you will need to
add a ModelValue:
ModelState.AddModelError(“Name”,“Bad
Name”);

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

所以我更新了我的代码如下：

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(或尽可能多的)验证,包括必填字段和b.我在验证摘要中想要我自己的邮件(例如“FieldX是必填字段”,而不是“需要一个值”).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

（编辑：李大同）

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