Question

I’m trying to refresh my memory but can’t find answers with Google.

public class BaseClass
{
    public virtual void DoSomething()
    {
        Trace.Write("base class");
    }
}

public class DerivedClass : BaseClass
{
    public override void DoSomething()
    {
        Trace.Write("derived class");
    }
}

If I create an instance of derived class, how do I convert it to it’s base class so that when DoSomething() is called, it uses the base class’s method only?

A dynamic cast still calls the derived class’s overridden method:

DerivedClass dc = new DerivedClass();

dc.DoSomething();

(dc as BaseClass).DoSomething();

Output: “derived class”

Answer 1

You can’t – that’s entirely deliberate, as that’s what polymorphism is all about. Suppose you have a derived class which enforces certain preconditions on the arguments you pass to an overridden method, in order to maintain integrity… you don’t want to be able to bypass that validation and corrupt its internal integrity.

Within the class itself you can non-virtually call base.AnyMethod() (whether that’s the method you’re overriding or not) but that’s okay because that’s the class itself deciding to potentially allow its integrity to be violated – presumably it knows what it’s doing.