如果没有将模型类的实例传递给视图，如何避免Create.cshtml中的EditorFor（x = x.Prop）生成的nullexception？

约束：

1. 我不想使用Nullable类型。
2. 我不想在HttpGet Create操作方法中实例化一个模型类。

型号类：

 namespace MvcTest.Models { public enum Gender { Male, Female } public class Person { public Gender Gender { get; set; } } } 

模板编辑助手（Gender.cshtml）：

 @using MvcTest.Models @model Gender @{ var genders = from Gender g in Enum.GetValues(typeof(Gender)) select new { Value = g, Text = g.ToString() }; var sl = new SelectList(genders, "Value", "Text", Model); } @Html.DropDownList(string.Empty, sl, "--Select--") 

控制器：

 using System.Web.Mvc; using MvcTest.Models; namespace MvcTest.Controllers { public class HomeController : Controller { public ActionResult Create() { //Person p = new Person(); //return View(p); return View(); } } } 

视图：

 @model MvcTest.Models.Person @using (Html.BeginForm()) { @Html.EditorFor(x => x.Gender) 
  
 } 

错误：

 Server Error in '/' Application. The model item passed into the dictionary is null, but this dictionary requires a non-null model item of type 'MvcTest.Models.Gender'. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: System.InvalidOperationException: The model item passed into the dictionary is null, but this dictionary requires a non-null model item of type 'MvcTest.Models.Gender'. Source Error: Line 3: { Line 4: Line 5: @Html.EditorFor(x => x.Gender) Line 6: 
 Line 7:  Source File: e:\MvcTest\MvcTest\Views\Home\Create.cshtml Line: 5 Stack Trace: [InvalidOperationException: The model item passed into the dictionary is null, but this dictionary requires a non-null model item of type 'MvcTest.Models.Gender'.] System.Web.Mvc.ViewDataDictionary`1.SetModel(Object value) +143 System.Web.Mvc.ViewDataDictionary..ctor(ViewDataDictionary dictionary) +377 System.Web.Mvc.WebViewPage`1.SetViewData(ViewDataDictionary viewData) +27 System.Web.Mvc.RazorView.RenderView(ViewContext viewContext, TextWriter writer, Object instance) +99 System.Web.Mvc.BuildManagerCompiledView.Render(ViewContext viewContext, TextWriter writer) +115 System.Web.Mvc.Html.TemplateHelpers.ExecuteTemplate(HtmlHelper html, ViewDataDictionary viewData, String templateName, DataBoundControlMode mode, GetViewNamesDelegate getViewNames, GetDefaultActionsDelegate getDefaultActions) +584 System.Web.Mvc.Html.TemplateHelpers.TemplateHelper(HtmlHelper html, ModelMetadata metadata, String htmlFieldName, String templateName, DataBoundControlMode mode, Object additionalViewData, ExecuteTemplateDelegate executeTemplate) +1027 System.Web.Mvc.Html.TemplateHelpers.TemplateHelper(HtmlHelper html, ModelMetadata metadata, String htmlFieldName, String templateName, DataBoundControlMode mode, Object additionalViewData) +66 System.Web.Mvc.Html.TemplateHelpers.TemplateFor(HtmlHelper`1 html, Expression`1 expression, String templateName, String htmlFieldName, DataBoundControlMode mode, Object additionalViewData, TemplateHelperDelegate templateHelper) +118 System.Web.Mvc.Html.TemplateHelpers.TemplateFor(HtmlHelper`1 html, Expression`1 expression, String templateName, String htmlFieldName, DataBoundControlMode mode, Object additionalViewData) +100 System.Web.Mvc.Html.EditorExtensions.EditorFor(HtmlHelper`1 html, Expression`1 expression) +57 ASP._Page_Views_Home_Create_cshtml.Execute() in e:\MvcTest\MvcTest\Views\Home\Create.cshtml:5 System.Web.WebPages.WebPageBase.ExecutePageHierarchy() +207 System.Web.Mvc.WebViewPage.ExecutePageHierarchy() +81 System.Web.WebPages.StartPage.RunPage() +19 System.Web.WebPages.StartPage.ExecutePageHierarchy() +65 System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext, TextWriter writer, WebPageRenderingBase startPage) +76 System.Web.Mvc.RazorView.RenderView(ViewContext viewContext, TextWriter writer, Object instance) +220 System.Web.Mvc.BuildManagerCompiledView.Render(ViewContext viewContext, TextWriter writer) +115 System.Web.Mvc.ViewResultBase.ExecuteResult(ControllerContext context) +303 System.Web.Mvc.ControllerActionInvoker.InvokeActionResult(ControllerContext controllerContext, ActionResult actionResult) +13 System.Web.Mvc.c__DisplayClass1c.b__19() +23 System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilter(IResultFilter filter, ResultExecutingContext preContext, Func`1 continuation) +260 System.Web.Mvc.c__DisplayClass1e.b__1b() +19 System.Web.Mvc.ControllerActionInvoker.InvokeActionResultWithFilters(ControllerContext controllerContext, IList`1 filters, ActionResult actionResult) +177 System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName) +343 System.Web.Mvc.Controller.ExecuteCore() +116 System.Web.Mvc.ControllerBase.Execute(RequestContext requestContext) +97 System.Web.Mvc.ControllerBase.System.Web.Mvc.IController.Execute(RequestContext requestContext) +10 System.Web.Mvc.c__DisplayClassb.b__5() +37 System.Web.Mvc.Async.c__DisplayClass1.b__0() +21 System.Web.Mvc.Async.c__DisplayClass8`1.b__7(IAsyncResult _) +12 System.Web.Mvc.Async.WrappedAsyncResult`1.End() +62 System.Web.Mvc.c__DisplayClasse.b__d() +50 System.Web.Mvc.SecurityUtil.b__0(Action f) +7 System.Web.Mvc.SecurityUtil.ProcessInApplicationTrust(Action action) +22 System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +60 System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result) +9 System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +8862381 System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +184 Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.225 

问题：当没有将模型类的实例传递给视图时，如何避免Create.cshtml中的EditorFor（x = x.Prop）生成的nullexception？

Answer 1

AFAIK你需要使用可空的枚举来实现这一目标。 它也有意义，因为当未选择值（ --SELECT-- ）时，枚举必须为空。 这是一篇关于有用的扩展方法的好文章 。