How to handle a class you want to extend which is sealed in the .NET library?

Question

I was reading somewhere about how to handle the issue of wanting to extend a sealed class in the .NET Framework library.

This is often a common and useful task to do

Answer 1

There is 'fake' inheritance. That is, you implement the base class and any interfaces the other class implements:

// Given
sealed class SealedClass : BaseClass, IDoSomething { }

// Create
class MyNewClass : BaseClass, IDoSomething { }

You then have a private member, I usually call it _backing, thus:

class MyNewClass : BaseClass, IDoSomething
{
   SealedClass _backing = new SealedClass();
}

This obviously won't work for methods with signatures such as:

void NoRefactoringPlease(SealedClass parameter) { }

If the class you want to extend inherits from ContextBoundObject at some point, take a look at this article. The first half is COM, the second .Net. It explains how you can proxy methods.

Other than that, I can't think of anything.