How to get the class Type in a base class static method in .NET?

Question

All I want to do is similar to:

public abstract class BaseClass
{
    public static Type GetType()
    {
        return typeof(BaseClass);
    }
}

But when I derive it

public class DerivedClass : BaseClass
{
}

I want to get

Assert.AreEqual(typeof(DerivedClass), DerivedClass.GetType());

How to change the BaseClass to make this assertion true?

This doesn't make any sense. Why would you want to call `GetType` from a static method? — Gabe, Jan 12 '11 at 13:22
@asawyer @Marc I correct the sample, now it compiles and I tested it — Jader Dias, Jan 12 '11 at 15:27
@Gabe It's an oversimplified example, that's why it doesn't make sense. — Jader Dias, Jan 12 '11 at 15:28
@Marc @Gabe Actually `GetType` in my code (not in the example) is `CreateServiceHost` which needs to know which of the derived service classes is calling it. — Jader Dias, Jan 12 '11 at 15:30
You haven't explained why you need a static method? What's your end goal? — Gabe, Jan 12 '11 at 15:33
@Gabe is to create `ServiceHost` which uses the type of the current class as an argument to its constructor — Jader Dias, Jan 12 '11 at 15:35
@Jeff I don't need to instantiate the service class to instantiate a ServiceHost. But I gave up of this question already since you answered it. — Jader Dias, Jan 12 '11 at 15:46
See https://stackoverflow.com/questions/3064227/get-derived-class-type-from-a-bases-class-static-method — Crescent Fresh, Jun 15 '20 at 02:26

score 2 · Answer 1 · answered Jan 12 '11 at 13:17

You can't do this because your only route to a derived type from one of its bases is from an instance - and static methods don't take an instance.

I'm hoping that your example is for simplicity because otherwise re-implementing GetType() seems a bit pointless - since the object.GetType() will do exactly what you want.

If you actually need to do this via a statically invoked method - you can't because no type information is actually available to a static method (as I say in the first paragraph).

If you actually invoking this method via an instance (but I must ask why!?) then you can do one of the following

a) Make your method an instance method on the base. It can then do this.GetType() (using the .Net base method) and it'll return the ultimate subtype of the instance.

b) Define an extension method for BaseClass that does something very similar:

public static Type GetType2(this BaseClass instance)
{
  return instance.GetType();
}

score 2 · Accepted Answer · answered Jan 12 '11 at 15:37

Static methods are not inherited.

The compiler substitutes BaseClass for DerivedClass when calling a base class' static methods through one of its derived classes. For example, here's the IL code for a call to DerivedClass.GetType():

IL_0002:  call   class [mscorlib]System.Type Tests.Program/BaseClass::GetType()

How to get the class Type in a base class static method in .NET?

2 Answers2

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