namespace ObserverPattern{    public interface ISubject    {        event EventHandler NotifyHandler;     }    public class CstEventArg : EventArgs    {        public string Name { get; set; }    }    public class News : ISubject    {        public event EventHandler NotifyHandler;        public void NotifyChanges(EventArgs e)        {            if (NotifyHandler != null)            {                NotifyHandler(null, e);            }        }    }    public class CommonOne    {        public CommonOne(ISubject subject)        {            subject.NotifyHandler += ShowInConsole;        }        public void ShowInConsole(object sender, EventArgs e)        {            Console.WriteLine("show in console " + (e as CstEventArg).Name);        }    }    public class CommonTwo    {        public CommonTwo(ISubject subject)        {            subject.NotifyHandler += ShowInConsole;        }        public void ShowInConsole(object sender, EventArgs e)        {            Console.WriteLine("show in WPF " + (e as CstEventArg).Name);        }    }    class Program    {        static void Main(string[] args)        {            News news = new News();            CommonOne cp1 = new CommonOne(news);            CommonTwo cp2 = new CommonTwo(news);            news.NotifyChanges(new CstEventArg() { Name = "abc" });            Console.ReadLine();        }    }}