ModelMetaData,自定义类属性和难以形容的问题

Question

我想做的事情似乎很简单.

在我的index.cshtml中,我想显示WizardStepAttributeValue

因此,用户将在每个页面的顶部看到 Step 1: Enter User Information

---

我有一个名为的ViewModel WizardViewModel.这个ViewModel有一个属性IList<IStepViewModel> Steps

每个"步骤"实现接口IStepViewModel,这是一个空接口.

我有一个名为Index.cshtml的视图.此视图显示EditorFor()当前步骤.

我有一个自定义的ModelBinder,它将View绑定到IStepViewModel基于该WizardViewModel.CurrentStepIndex属性实现的具体类的新实例

我创建了一个自定义属性WizardStepAttribute.

我的每个步骤类都是这样定义的.

[WizardStepAttribute(Name="Enter User Information")] 
[Serializable]
public class Step1 : IStepViewModel
....

我有几个问题.

我的视图是强类型的,WizardViewModel不是每一步.我不想为每个具体实现创建一个视图IStepViewModel

我以为我可以在界面中添加属性,但是我必须在每个类中明确地实现它.(所以这不是更好)

我想我可以在界面中使用反射来实现它,但是,你不能在接口中的方法中引用实例.

Answer 1

它可以做到,但既不容易也不漂亮.

首先,我建议在WizardStepAttribute类StepNumber中添加第二个字符串属性,以便您的WizardStepAttribute类如下所示:

[AttributeUsage(AttributeTargets.All, AllowMultiple = false)]
public class WizardStepAttribute : Attribute
{
    public string StepNumber { get; set; }
    public string Name { get; set; }
}

然后,每个班级必须装饰:

[WizardAttribute(Name = "Enter User Information", StepNumber = "1")]
public class Step1 : IStepViewModel
{
    ...
}

接下来,您需要创建自定义DataAnnotationsModelMetadataProvider,以获取自定义属性的值并将它们插入Step1模型的元数据中:

public class MyModelMetadataProvider : DataAnnotationsModelMetadataProvider 
{
    protected override ModelMetadata CreateMetadata(
        IEnumerable<Attribute> attributes,
        Type containerType,
        Func<object> modelAccessor,
        Type modelType,
        string propertyName)
    {
        var modelMetadata = base.CreateMetadata(attributes, containerType, modelAccessor, modelType, propertyName);
        var additionalValues = attributes.OfType<WizardStepAttribute>().FirstOrDefault();

        if (additionalValues != null)
        {
            modelMetadata.AdditionalValues.Add("Name", additionalValues.Name);
            modelMetadata.AdditionalValues.Add("StepNumber", additionalValues.StepNumber);
        }
        return modelMetadata;
    }
}

然后,为了呈现您的自定义元数据,我建议您创建一个自定义HtmlHelper来为每个视图创建标签:

    [SuppressMessage("Microsoft.Design", "CA1006:DoNotNestGenericTypesInMemberSignatures", Justification = "This is an appropriate nesting of generic types")]
    public static MvcHtmlString WizardStepLabelFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression)
    {
        return WizardStepLabelFor(htmlHelper, expression, null /* htmlAttributes */);
    }

    [SuppressMessage("Microsoft.Design", "CA1006:DoNotNestGenericTypesInMemberSignatures", Justification = "This is an appropriate nesting of generic types")]
    public static MvcHtmlString WizardStepLabelFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, object htmlAttributes)
    {
        return WizardStepLabelFor(htmlHelper, expression, new RouteValueDictionary(htmlAttributes));
    }

    [SuppressMessage("Microsoft.Design", "CA1011:ConsiderPassingBaseTypesAsParameters", Justification = "Users cannot use anonymous methods with the LambdaExpression type")]
    [SuppressMessage("Microsoft.Design", "CA1006:DoNotNestGenericTypesInMemberSignatures", Justification = "This is an appropriate nesting of generic types")]
    public static MvcHtmlString WizardStepLabelFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression, IDictionary<string, object> htmlAttributes)
    {
        if (expression == null)
        {
            throw new ArgumentNullException("expression");
        }
        ModelMetadata metadata = ModelMetadata.FromLambdaExpression(expression, htmlHelper.ViewData);
        var values = metadata.AdditionalValues;

        // build wizard step label
        StringBuilder labelSb = new StringBuilder();
        TagBuilder label = new TagBuilder("h3");
        label.MergeAttributes(htmlAttributes);
        label.InnerHtml = "Step " + values["StepNumber"] + ": " + values["Name"]; 
        labelSb.Append(label.ToString(TagRenderMode.Normal));

        return new MvcHtmlString(labelSb.ToString() + "\r");
    }

如您所见,自定义帮助程序使用您的自定义元数据创建一个h3标记.

然后,最后,在您看来,输入以下内容:

@Html.WizardStepLabelFor(model => model)

两个注意事项:首先,在Global.asax.cs文件中,将以下内容添加到Application_Start():

        ModelMetadataProviders.Current = new MyModelMetadataProvider();

其次,在Views文件夹的web.config中,确保为自定义HtmlHelper类添加命名空间:

<system.web.webPages.razor>
  <host factoryType="System.Web.Mvc.MvcWebRazorHostFactory, System.Web.Mvc, Version=3.0.0.0, Culture=neutral, PublicKeyToken=31BF3856AD364E35" />
  <pages pageBaseType="System.Web.Mvc.WebViewPage">
    <namespaces>
      <add namespace="System.Web.Mvc" />
      <add namespace="System.Web.Mvc.Ajax" />
      <add namespace="System.Web.Mvc.Html" />
      <add namespace="System.Web.Routing" />
      <add namespace="YOUR NAMESPACE HERE"/>
    </namespaces>
  </pages>
</system.web.webPages.razor>

瞧.

counsellorben