ASP.NET Web API uses a completely different ModelBinding insfracture than APS.NET MVC.
You are trying to implement the MVC's model binder interface System.Web.Mvc.IModelBinder
but to work with Web API you need to implement System.Web.Http.ModelBinding.IModelBinder
So your implementation should look like this:
public class MyModelBinder : System.Web.Http.ModelBinding.IModelBinder
{
public MyModelBinder()
{
}
public bool BindModel(
System.Web.Http.Controllers.HttpActionContext actionContext,
System.Web.Http.ModelBinding.ModelBindingContext bindingContext)
{
// Implementation
}
}
For further reading: