Question

I’m trying to not repeat code, so I have a method that does a quick transform on the property of an interface.

I have 3 concrete classes that make use of this interface, and I want them all to be able to use this method.

The problem comes when I get one of these objects out of Session. I don’t see any way to cast it properly.

public ActionResult GetItems()
{
     details = (IHeader<IDetail>)Session["SelectedHeader"].Details // Throws invalid cast
     return Json(details);
}

// My interface and class examples:
interface IHeader<T> where T: IDetail
{
     IList<T> Details { get; set; }
}

class ConcreteHeader : IHeader<ConcreteDetail>
{
     public IList<ConcreteDetail> Items { get; set; }
}

class ConcreteDetail : IDetail
{
    ...
}

I can’t use generics because this is an action method in ASP.NET MVC 3 (unless there is a trick to that). Is this possible, or do I have to write a method for each class?

EDIT: Not sure if this is clear from original question:

What goes into session is any one of the concrete objects:

Session["SelectedHeader"] = new ConcreteHeader() { Details = new List<ConcreteDetail>() };

Answer 1

If you’re using .NET 4.0, simply cast using the dynamic keyword to ensure proper automagical type resolution:

// note intellisense won't work when you use dynamic keyword...
var details = ((dynamic)Session["SelectedHeader"]).Details;