Asp MVC 3: Modifiy Values Sent to View

Question

as far as I understand a ModelBinder can generate class instances out of routedata/formdata.

What I'm looking for is a way to manipulate the data handed over to the view before it is consumed by the view.

What are the possiblities? Do I miss something obvious?

Thanks in advance!

EDIT
I don't want to send clear IDs to the client but encrypt them (at least in edit cases). As it happens very often I want this step as much as possible automated.
I look for something like a ModelBinder or a Attribute to attach to a method/viewmodel/...

Example:
GET

public ActionResult Edit(int id)
{
    var vm = new EditArticleViewModel();

    ToViewModel(repository.Get<Article>(id), vm);

    return View(vm); // id is something like 5 and should be encryped before being used by the view
}

View

@model EditArticleViewModel

<div>
    @Html.HiddenFor(x => x.Id) <!-- x.Id should be encrypted, not just "5" -->
    ...
</div>

Lg warappa

Answer 1

You could do something with an action filter:

public class EncryptIDAttribute : ActionFilterAttribute
{
    public override void OnActionExecuted(ActionExecutedContext filterContext)
    {
        var vm = filterContext.Controller.ViewData.Model as EditArticleViewModel;

        if(vm != null)
        {
            vm.ID = SomeMethodToEncrypt(vm.ID);
        }
    }
}

and apply it to any relevent actions:

[EncryptID]
public ActionResult Edit(int id)
{
    var vm = new EditArticleViewModel();

    ToViewModel(repository.Get<Article>(id), vm);

    return View(vm);
}

When the page is then posted you can use a model binder to decrypt the id.

If you then wanted to apply this across multiple view models you could look at creating a custom data annotation which flags a property to be encrypted. In your action filter you can then look for any properties with this data annotation and encrypt them accordingly.

Answer 2

You could write a custom HiddenFor helper method that will automatically encrypt the value:

public static class HiddenExtensions
{
    public static MvcHtmlString HiddenForEncrypted<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> ex)
    {
        var metadata = ModelMetadata.FromLambdaExpression(ex, htmlHelper.ViewData);
        var name = ExpressionHelper.GetExpressionText(ex);
        var value = metadata.Model;
        var encryptedValue = SomeFunctionToEncrypt(value);
        return htmlHelper.Hidden(name, encryptedValue);
    }
}

As an alternative you could use the Html.Serialize helper in the MVCFutures assembly that does this under the covers.

So basically you will write in your view:

@Html.Serialize("id", Model.Id, SerializationMode.Encrypted)

and in your controller:

public ActionResult Edit([Deserialize(SerializationMode.Encrypted)]int id)
{
    ...
}