Hi,

  I Can do it with Covarience like below sample. I want to handle common variable.

     public class Program
    {
        static void Main(string[] args)
        {

        

            IGenericFactory<IAnimal> hayvan = new GenericFactory<Cat>();
            hayvan = new GenericFactory<Dog>();

            IAnimal cat = hayvan2.Create();
            cat.Speak();
            Console.ReadLine();


        }
    }



   public interface IAnimal
    {
        void Speak();
    }

    public class Cat : IAnimal
    {
        public void Speak()
        {
            Console.WriteLine("Miyaww");
        }
    }

    public class Dog : IAnimal
    {
        public void Speak()
        {
            Console.WriteLine("Hqw haww");
        }
    }




    public interface IGenericFactory<out T>
    {
        T Create();
    }

    public class GenericFactory<T> : IGenericFactory<T> where T : IAnimal, new()
    {

        public GenericFactory() { }

        public T Create()
        {
            return new T();
        }

    }

Best Regards.