某一对象由于有不同的状态，而产生不同的行为。

 

using System;using System.Collections;using System.Collections.Generic;using System.Linq;namespace ConsoleApplication1{    class Program    {        public interface IDoorState        {            void Switch(Door door);        }        public class DoorOn : IDoorState        {            public void Switch(Door door)            {                Console.WriteLine("door off");                door.DoorState = new DoorOff();            }        }        public class DoorOff : IDoorState        {            public void Switch(Door door)            {                Console.WriteLine("door on");                door.DoorState = new DoorOn();            }        }        public class Door        {            public IDoorState DoorState            {                get;                set;            }            public Door()            {                DoorState = new DoorOff();            }            public void Switch()            {                DoorState.Switch(this);            }        }        static void Main(string[] args)        {            Door door = new Door();            door.Switch();            door.Switch();            door.Switch();        }    }}