Calling child class method from parent

Question

Is it possible for the a.doStuff() method to print "B did stuff" without editing the A class? If so, how would I do that?

class Program
{
    static void Main(string[] args)
    {
        A a = new A();
        B b = new B();

        a.doStuff();
        b.doStuff();

        Console.ReadLine();
    }
}

class A
{
    public void doStuff()
    {
        Console.WriteLine("A did stuff");
    }
}

class B : A
{
    public void doStuff()
    {
        Console.WriteLine("B did stuff");
    }
}

I'm modding a steam game, Terraria. And I don't want to decompile and recompile it all because that will screw with steam. My program 'injects' into Terraria via XNA. I can use the update() and draw() methods from XNA to mod some things. But it's pretty limited. I wan't to override base methods to mod more things (worldgen for example).

Answer 1

Yes, if you declare doStuff as virtual in A and then override in B.

class A
{
    public virtual void doStuff()
    {
        Console.WriteLine("A did stuff");
    }
}

class B : A
{
    public override void doStuff()
    {
        Console.WriteLine("B did stuff");
    }
}

Answer 2

The code for class A & B you have posted will anyways generate below compiler warning and will ask to use the new keyword on class B, although it will compile: The keyword new is required on 'B.doStuff()' because it hides inherited member 'A.doStuff()'

Use method hiding along with new and virtual keyword in class Mapper and class B as follows:

class Program
{
    static void Main(string[] args)
    {
        Mapper a = new B(); //notice this line
        B b = new B();

        a.doStuff();
        b.doStuff();

        Console.ReadLine();
    }
}

class A
{
    public void doStuff()
    {
        Console.WriteLine("A did stuff");
    }
}

class Mapper : A
{
    new public virtual void doStuff() //notice the new and virtual keywords here which will all to hide or override the base class implementation
    {
        Console.WriteLine("Mapper did stuff");
    }
}

class B : Mapper
{
    public override void doStuff()
    {
        Console.WriteLine("B did stuff");
    }
}

Answer 3

Since B is effectively A through inheritance and the method is overloaded.

A a = new B();
a.doStuff();