Observer Pattern

When there are relationships between one or more objects, an observer will notify all the dependent elements when something is modified in the parent. Microsoft already implemented this pattern as ObservableCollection. Here let me implement the most basic Observer Pattern.

http://3.bp.blogspot.com/_DSP5FXX4Isw/S_RiTK0AChI/AAAAAAAAC-A/HE0zLdsm1rM/s320/observer.JPG

public delegate  void NotifyChangeEventHandler(string notifyinfo);
    public interface  IObservable
    {
        void Attach(NotifyChangeEventHandler ohandler);
        void Detach(NotifyChangeEventHandler ohandler);
        void Notify(string name);
    }
     
    public abstract  class AbstractObserver : IObservable
    {
        public void  Register(NotifyChangeEventHandler handler)
        {
            this.Attach(handler);
        }
 
        public void  UnRegister(NotifyChangeEventHandler handler)
        {
            this.Detach(handler);
        }
 
        public virtual  void ChangeState()
        {
            this.Notify("ChangeState");
             
        }
 
        #region IObservable Members
 
        public void  Attach(NotifyChangeEventHandler ohandler)
        {
            this.NotifyChanged += ohandler;
        }
 
        public void  Detach(NotifyChangeEventHandler ohandler)
        {
            this.NotifyChanged -= ohandler;
        }
 
        public void  Notify(string  name)
        {
            if (this.NotifyChanged != null)
                this.NotifyChanged(name);
        }
 
        #endregion
 
        #region INotifyChanged Members
 
        public event  NotifyChangeEventHandler NotifyChanged;
 
        #endregion
    }
 
    public class  Observer : AbstractObserver 
    {
        public override  void ChangeState()
        {
            //Do something.
            base.ChangeState();
             
        }
    }

You can definitely got the idea that after you Register for the Notification, you will get it when ChangeState is called.