Type-directed serialization in ValueProvider - asp.net-mvc

Question

I was hoping to encapsulate all the serialization logic of my json api using the ValueProvider facility of MS.NET MVC.
However, since my deserialization is type directed (i.e. it needs to know what class to return from deserializing), and I can simply find no reasonable way to get to the type that my ValueProvider is supposed to return.
Suppose we have a controller:
public class MyController : Controller
{
// We want obj to be instantiated by MyValueProvider
public ActionResult MyAction(MyComplexObject obj)
{
}
}
What I would then like to be able to write:
public class MyValueProvider : IValueProvider
{
public bool ContainsPrefix(string prefix)
{
...
}
public ValueProviderResult GetValue(string key)
{
switch (req.HttpMethod)
{
case "POST":
{
req.InputStream.Position = 0;
T retObj = MyDeserialize<T>(req.InputStream);
return new ValueProviderResult(retObj, key, CultureInfo.CurrentCulture);
}
break;
default:
return null;
}
}
}
(Though I realise that without actually binding T in MyValueProvider I would have to use reflection to invoke MyDeserialize with a runtime-provided Type)
I'm almost considering to just derive the runtime type to deserialize using some variable naming scheme keyed by the 'key' argument to GetValue.

Answer 1

After spending half day pondering this, and then reading http://ishwor.cyberbudsonline.com/2012/07/fun-with-aspnet-mvc-3-custom-json-model-binder.html, I have come to the conclusion that what I need is in fact a ModelBinder, as the ModelType is available in the BindingContext.
So, the ValueProvider in the question becomes:
public class MyModelBinder<T> : IModelBinder
{
public object BindModel(
ControllerContext controllerContext,
ModelBindingContext bindingContext)
{
JToken resTok;
var key = bindingContext.ModelName;
var req = controllerContext.HttpContext.Request;
if (bindingContext.ModelType != typeof(T)) return null;
switch (req.HttpMethod)
{
case "POST":
req.InputStream.Position = 0;
T retObj = MyDeserialize<T>(req.InputStream);
return retObj;
break;
default:
return null;
}
}
}