ModelMetaData, user class attributes and indescribable question

Question

What I want to do seems so simple.

In my index.cshtml I want to display the WizardStepAttributevalue

So the user will see at the top of each page Step 1: Enter User Information

---

I have a ViewModel called WizardViewModel. This ViewModel has a propertyIList<IStepViewModel> Steps

each "step" implements the IStepViewModel interface, which is an empty interface.

I have a view called Index.cshtml. This view displays the EditorFor()current step.

I have a custom ModelBinder that associates a view with a new instance of a specific class that implements IStepViewModelbased on a propertyWizardViewModel.CurrentStepIndex

I created a custom attribute WizardStepAttribute.

Each of my Steps classes is defined as follows.

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

I have a few issues.

My view is strictly typed at WizardViewModelnot every step. I do not want to create a view for each specific implementationIStepViewModel

I thought I could add a property to the interface, but then I must explicitly implement it in each class. (So ​​it's not better)

I think I can implement it using reflection in the interface, but you cannot reference instances in methods in the interface.

Answer 1

It can be done, but it is not easy and beautiful.

-, WizardStepAttribute, StepNumber, WizardStepAttribute :

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

:

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

DataAnnotationsModelMetadataProvider, Step1:

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;
    }
}

, , HtmlHelper :

    [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");
    }

, h3 .

, , , :

@Html.WizardStepLabelFor(model => model)

: -, Global.asax.cs Application_Start():

        ModelMetadataProviders.Current = new MyModelMetadataProvider();

-, web.config "" HtmlHelper:

<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>

Voila.

counsellorben

Answer 2

, IMetadataAware:

https://msdn.microsoft.com/en-us/library/system.web.mvc.imetadataaware(v=vs.118).aspx

:

public class WizzardStepAttribute : Attribute, IMetadataAware
{
    public string Name;

    public void OnMetadataCreated(ModelMetadata metadata)
    {
        if (!metadata.AdditionalValues.ContainsKey("WizzardStep"))
        {
            metadata.AdditionalValues.Add("WizzardStep", Name);
        }
    }
}