Interfaces - Implement abstract class methods

Question

I'm not exactly sure how to ask this question, but basically what I want to do is access the abstract methods from IDog. Consider this:

    static void Main(string[] args)
    {
        IDog dog = new Dog();
        dog.CatchFrisbee();
        dog.Speak("Bark") // error -> no implementation
        Console.ReadLine();
    }

    public class Dog : Animal, IDog
    {
        public void CatchFrisbee()
        {
            Console.WriteLine("Dog Catching Frisbee");
        }
    }
    public abstract class Animal : IAnimal
    {
        public void Speak(string sayWhat)
        {
            Console.WriteLine(sayWhat);
        }

        public void Die()
        {
            Console.WriteLine("No Longer Exists");
        }
    }
    public interface IDog
    {
        void CatchFrisbee();
    }
    public interface IAnimal
    {
        void Die();

        void Speak(string sayWhat);
    }

From my static void Main, I would like to be able to call dog.Speak() but I can't because it's not implemented in IDog. I know I can easily access Speak() from my derived classes but is it possible to access it from the implemenation or would that be a bad design?

spender · Accepted Answer · 2015-04-29 17:28:36Z

6

Assuming that all IDogs are IAnimals, declare IDog as implementing IAnimal

public interface IDog : IAnimal

answered Apr 29, 2015 at 17:28

spender

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6 Comments

Anonymous Over a year ago

@spender Thanks for the answer! I'm trying to become more disciplined in OOP practices and ran into an issue where I thought this would be beneficial. Is this something that is common because I was speaking to another developer and she asked why I wanted to do this as if it was a bad design. Thanks again!

pseudocoder Over a year ago

Could you explain the principle that keeps Dog from inheriting Speak() since it Dog inherits Animal and Animal implements Speak()?

Ron Beyer Over a year ago

@pseudocoder because IDog isn't an IAnimal, Dog is. Dog can be cast to IAnimal or Animal, but IAnimal can't be cast to IDog or the other way around.

Anonymous Over a year ago

@pseudocoder Yes, it would be available if it was Dog

Ron Beyer Over a year ago

@pseudocoder yes, see the other answers, they are valid and work, but the architecture is the root of the problem.

|

Darren · Accepted Answer · 2015-04-29 17:30:42Z

1

You could perform a cast:

 ((Animal) dog).Speak("Bark");

Or take advantage of multiple interface inheritance:

public interface IDog : IAnimal
{
    void CatchFrisbee();
}

answered Apr 29, 2015 at 17:30

Darren

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