ASP.NET MVC3 中的 Razor 和接口继承：为什么找不到这个属性？

Question

我在 ASP.NET MVC3 应用程序中的一个 Razor 视图有一个奇怪的问题。当我将属性的值写入调试器控制台时，我收到一条错误消息，告诉我无法找到该属性。

我的视图将一个名为 FormEditViewModel 的类作为其模型。 FormEditViewModel 具有 IForm 类型的属性，该接口继承自另一个接口 IFormObject。 IFormObject 定义了一个属性 Name，因此任何实现 IForm 的东西都必须实现一个名为 Name 的属性。具体类型Form实现了IForm接口，并根据需要定义了一个Name属性。

当我运行代码并检查传递给 View 的 FormEditViewModel 对象时，我可以看到它有一个 IForm 类型的属性 Form，并且这个 Form 对象有一个 Name 属性。如果我在控制器中插入以下行，以便在将 FormEditViewModel.Name 的值传递给视图之前将其写出，输出窗口会显示正确的名称：

Debug.WriteLine("Name: " + vm.Form.Name);

但是，当我运行视图时，我收到一条错误消息，提示“找不到属性 MyCompany.MyApplication.Domain.Forms.IForm.Name。”为什么 Razor 找不到 Name 属性，而控制器中的 C# 代码明明可以？

我的观点是这样的。引发异常的行是 @Html.LabelFor(model => model.Form.Name, "Form title")。

@using MyCompany.MyApplication.ViewModels;
@model FormEditViewModel
@{
    ViewBag.Title = "Edit form";
}
<script src="@Url.Content("~/Scripts/jquery.validate.min.js")" type="text/javascript"></script>
<script src="@Url.Content("~/Scripts/jquery.validate.unobtrusive.min.js")" type="text/javascript"></script>
<div class="MyApplicationcontainer">
    @using (Html.BeginForm("UpdateForm", "ZooForm"))
    {
        <div class="formHeader">
            @Html.ValidationSummary(true)
            @Html.Hidden("id", Model.Form.ZooFormId)
            <div id="editFormTitleDiv">
                <div class="formFieldContainer">
                    @Html.Label("Form ID")
                    @Html.TextBoxFor(m => m.Form.ZooFormId, new { @disabled = true })
                </div>
                <div class="formFieldContainer">
                    @Html.LabelFor(model => model.Form.Name, "Form title")
                    @Html.EditorFor(model => model.Form.Name)
                    @Html.ValidationMessageFor(model => model.Form.Name)
                </div>
                ...

这是视图模型：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using MyCompany.MyApplication.Domain.Forms;
using MyCompany.App.Web.ViewModels;

namespace MyCompany.MyApplication.ViewModels
{
    public class FormEditViewModel : ViewModelBase
    {
        public IForm Form { get; set; }
        public int Id
        {
            get { return Form.ZooFormId; }
        }
        public IEnumerable<Type> Types { get; set; }
        public Dictionary<string, string> FriendlyNamesForTypes { get; set; }
        public Dictionary<string, string> FriendlyNamesForProperties { get; set; }
        public IEnumerable<String> PropertiesForUseInForms { get; set; }
        public ObjectBrowserTreeViewModel ObjectBrowserTreeViewModel { get; set; }
    }
}

Form 对象真的很长，所以我不会在这里粘贴整个东西。它是这样声明的：

public class Form : FormObject, IForm

Form 对象不会重新定义 Name 属性，而是从 FormObject 类继承它。 FormObject 开头是这样的：

public abstract class FormObject : IFormObject

这里是接口IForm。如您所见，它没有声明 Name 成员，而是希望从 IFormObject 继承它：

using System;
namespace MyCompany.MyApplication.Domain.Forms
{
    public interface IForm : IFormObject
    {
        bool ContainsRequiredFields();
        MyCompany.MyApplication.Domain.Forms.Factories.IFormFieldFactory FormFieldFactory { get; }
        MyCompany.MyApplication.Domain.Forms.Factories.IFormPageFactory FormPageFactory { get; }
        string FriendlyName { get; set; }
        System.Collections.Generic.List<IFormField> GetAllFields();
        System.Collections.Generic.IEnumerable<DomainObjectPlaceholder> GetObjectPlaceholders();
        System.Collections.Generic.IEnumerable<IFormField> GetRequiredFields();
        System.Collections.Generic.IEnumerable<MyCompany.MyApplication.Models.Forms.FormObjectPlaceholder> GetRequiredObjectPlaceholders();
        System.Collections.Generic.List<IFormSection> GetSectionsWithMultipliableOption();
        MyCompany.MyApplication.BLL.IHighLevelFormUtilities HighLevelFormUtilities { get; }
        int? MasterId { get; set; }
        DomainObjectPlaceholder MasterObjectPlaceholder { get; set; }
        MyCompany.MyApplication.Domain.Forms.Adapters.IObjectPlaceholderAdapter ObjectPlaceholderAdapter { get; }
        MyCompany.MyApplication.Domain.Forms.Adapters.IObjectPlaceholderRelationshipAdapter ObjectPlaceholderRelationshipAdapter { get; }
        System.Collections.Generic.List<IFormPage> Pages { get; set; }
        MyCompany.MyApplication.Repository.IAppRepository AppRepo { get; set; }
        int ZooFormId { get; }
        MyCompany.MyApplication.BLL.IPocoUtils PocoUtils { get; }
        void RemoveSectionWithoutChangingDatabase(int sectionId);
        int? TopicId { get; set; }
        DomainObjectPlaceholder TopicObjectPlaceholder { get; set; }
        System.Collections.Generic.IEnumerable<FluentValidation.Results.ValidationResult> ValidationResults { get; set; }
    }
}

这里是接口IFormObject：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace MyCompany.MyApplication.Domain.Forms
{
    public interface IFormObject
    {
        string Name { get; }
        string LongName { get; }
        Guid UniqueId { get; }
        string Prefix { get; }
        string IdPath { get; set; }
        string IdPathWithPrefix { get; }
    }
}

问题是，为什么当我运行 Razor 视图时会出现以下异常，因为我本来希望 IForm 从 IFormObject 继承其 Name 属性？

Server Error in '/' Application.

The property MyCompany.MyApplication.Domain.Forms.IForm.Name could not be found.

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.ArgumentException: The property MyCompany.MyApplication.Domain.Forms.IForm.Name could not be found.

Source Error: 


Line 24:                 </div>
Line 25:                 <div class="formFieldContainer">
Line 26:                     @Html.LabelFor(model => model.Form.Name, "Form title")
Line 27:                     @Html.EditorFor(model => model.Form.Name)
Line 28:                     @Html.ValidationMessageFor(model => model.Form.Name)

Source File: c:\Users\me\Documents\Visual Studio 2010\Projects\zooDBMain\zooDB\zooDB\Views\ZooForm\Edit.cshtml    Line: 26 

Stack Trace: 


[ArgumentException: The property MyCompany.MyApplication.Domain.Forms.IForm.Name could not be found.]
   System.Web.Mvc.AssociatedMetadataProvider.GetMetadataForProperty(Func`1 modelAccessor, Type containerType, String propertyName) +505385
   System.Web.Mvc.ModelMetadata.GetMetadataFromProvider(Func`1 modelAccessor, Type modelType, String propertyName, Type containerType) +101
   System.Web.Mvc.ModelMetadata.FromLambdaExpression(Expression`1 expression, ViewDataDictionary`1 viewData) +421
   System.Web.Mvc.Html.LabelExtensions.LabelFor(HtmlHelper`1 html, Expression`1 expression, String labelText) +56
   ASP._Page_Views_ZooForm_Edit_cshtml.Execute() in c:\Users\me\Documents\Visual Studio 2010\Projects\zooDBMain\zooDB\zooDB\Views\ZooForm\Edit.cshtml:26
   System.Web.WebPages.WebPageBase.ExecutePageHierarchy() +272
   System.Web.Mvc.WebViewPage.ExecutePageHierarchy() +81
   System.Web.WebPages.StartPage.RunPage() +58
   System.Web.WebPages.StartPage.ExecutePageHierarchy() +94
   System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext, TextWriter writer, WebPageRenderingBase startPage) +173
   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.<InvokeActionResultWithFilters>b__19() +23
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilter(IResultFilter filter, ResultExecutingContext preContext, Func`1 continuation) +260
   System.Web.Mvc.<>c__DisplayClass1e.<InvokeActionResultWithFilters>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.<BeginProcessRequest>b__5() +37
   System.Web.Mvc.Async.<>c__DisplayClass1.<MakeVoidDelegate>b__0() +21
   System.Web.Mvc.Async.<>c__DisplayClass8`1.<BeginSynchronous>b__7(IAsyncResult _) +12
   System.Web.Mvc.Async.WrappedAsyncResult`1.End() +62
   System.Web.Mvc.<>c__DisplayClasse.<EndProcessRequest>b__d() +50
   System.Web.Mvc.SecurityUtil.<GetCallInAppTrustThunk>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() +8971485
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +184

Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.547

我很欣赏我的继承层次结构有点混乱，而且这不是最漂亮的代码，但我很想知道为什么会发生这种情况以及我有哪些解决方法。我是否无法理解接口继承在 C# 中的工作原理？

Answer 1

查看this 问题和this 一个问题。显然这是一个已知问题，解决方法似乎是：

<%: Html.HiddenFor(m => (m as IFormObject).Name) %>