Is there a way to make a constructor only visible

Question

I have a collection of classes that inherit from an abstract class I created. I'd like to use the abstract class as a factory for creating instances of concrete implementations of my abstract class.

Is there any way to hide a constructor from all code except a parent class.

I'd like to do this basically

public abstract class AbstractClass
{
    public static AbstractClass MakeAbstractClass(string args)
    {
        if (args == "a")
            return new ConcreteClassA();
        if (args == "b")
            return new ConcreteClassB();
    }
}

public class ConcreteClassA : AbstractClass
{
}

public class ConcreteClassB : AbstractClass
{
}

But I want to prevent anyone from directly instantiating the 2 concrete classes. I want to ensure that only the MakeAbstractClass() method can instantiate the base classes. Is there any way to do this?

UPDATE
I don't need to access any specific methods of ConcreteClassA or B from outside of the Abstract class. I only need the public methods my Abstract class provides. I don't really need to prevent the Concrete classes from being instantiated, I'm just trying to avoid it since they provide no new public interfaces, just different implementations of some very specific things internal to the abstract class.

To me, the simplest solution is to make child classes as samjudson mentioned. I'd like to avoid this however since it would make my abstract class' file a lot bigger than I'd like it to be. I'd rather keep classes split out over a few files for organization.

I guess there's no easy solution to this...

Answer 1

Can't you use the keyword partial for splitting the code for a class into many files?

Answer 2

Following on from the accepted answer, if you had a public interface and made the private classes implement the interface, you could then return a pointer to the interface and anyone outside of your parent abstract class could then use them (whilst still hiding the child classes).

Answer 3

If you are using this class in a seperate service assembly, you can use the internal keyword.

public class AbstractClass
{
    public AbstractClass ClassFactory(string args)
    {
        switch (args)
        {
            case "A":
                return new ConcreteClassA();               
            case "B":
                return new ConcreteClassB();               
            default:
                return null;
        }
    }
}

public class ConcreteClassA : AbstractClass
{
    internal ConcreteClassA(){ }
}

public class ConcreteClassB : AbstractClass
{
    internal ConcreteClassB() {}
}