状态模式

public class Account
    {
        public AccountState State { set; get; }
        public string Owner { set; get; }
        public double Balance { set; get; }

        public Account(string owner, double initialAmount)
        {
            Owner = owner;
            Balance = initialAmount;
            State = new VistorState(this);  //设置初始状态
        }

        public void SetBalance(double amount)
        {
            Balance = amount;

        }

        //存款
        public void Deposit(double amount)
        {
            Console.WriteLine("存入" + amount);
            State.Deposit(amount);
            Console.WriteLine("用户状态变为" + State._Statename);
        }

        //消费
        public void Shopping(double amount)
        {
            Console.WriteLine("消费" + amount);
            State.Shopping(amount);
            Console.WriteLine("用户状态变为" + State._Statename);
        }
    }

public abstract class AccountState
    {
        protected Account _account;
        public string _Statename;

        public abstract void Deposit(double amount);
        public abstract void Shopping(double amount);
        public abstract void StateCheck();
    }

public class MemberState:AccountState
    {
        public MemberState(Account account)
        {
            _account = account;
            _Statename = "会员账户";
        }

        //取款
        public override void Deposit(double amount)
        {
            _account.Balance += amount;
            Console.WriteLine(_account.Owner + " 向账户中存款" + amount + "元，存款后的账户余额为：" + _account.Balance);
            StateCheck();
        }

        //消费
        public override void Shopping(double amount)
        {
            double newBalance = _account.Balance - amount;
            if (newBalance > 0)
            {
                _account.Balance -= amount;
                Console.WriteLine(_account.Owner + "在《会员服务》中消费" + amount + "元，账户余额：" + _account.Balance);
            }
            else
            {
                Console.WriteLine("您的账户余额不足，请充值。");
            }
            StateCheck();
        }

        //检查用户状态
        public override void StateCheck()
        {
            if (_account.Balance > 0 && _account.Balance < 100)
            {
                //访客用户状态
                _account.State = new VistorState(_account);
            }
            else if (_account.Balance > 1000)
            {
                //贵宾用户状态
                _account.State = new VIPState(_account);

            }
        }
    }

class Program
    {
        static void Main(string[] args)
        {
            Account account = new Account("王大锤", 99);
            Console.WriteLine("开户成功。姓名：" + account.Owner + " 初始金额：" + account.Balance + " 账户类型：" + account.State._Statename);
            Console.WriteLine("----------------------------");

            account.Deposit(20);
            Console.WriteLine("-----------------------------");

            account.Shopping(30);
            Console.WriteLine("-----------------------------");

            account.Deposit(9999);
            Console.WriteLine("------------------------------");

            Console.ReadLine();
        }
    }

 public class VIPState:AccountState
    {
        public VIPState(Account account)
        {
            _account = account;
            _Statename = "贵宾账户";
        }

        //取款
        public override void Deposit(double amount)
        {
            _account.Balance += amount;
            Console.WriteLine(_account.Owner + " 向账户中存款" + amount + "元，存款后的账户余额为：" + _account.Balance);
            StateCheck();
        }

        //消费
        public override void Shopping(double amount)
        {
            double newBalance = _account.Balance - amount;
            if (newBalance > 0)
            {
                _account.Balance -= amount;
                Console.WriteLine(_account.Owner + "在《贵宾服务》中消费" + amount + "元，账户余额：" + _account.Balance);
            }
            else
            {
                Console.WriteLine("您的账户余额不足，请充值。");
            }
            StateCheck();
        }

        //检查用户状态
        public override void StateCheck()
        {
            if (_account.Balance > 0 && _account.Balance < 100)
            {
                //访客用户状态
                _account.State = new VistorState(_account);
            }
            else if (_account.Balance > 100&&_account.Balance<1000)
            {
                //会员用户状态
                _account.State = new MemberState(_account);
            }
        }
    }

public class VistorState:AccountState
    {
        public VistorState(Account account)
        {
            _account = account;
            _Statename = "访客账户";
            StateCheck();  //默认的检查
        }

        //取款
        public override void Deposit(double amount)
        {
            _account.Balance += amount;
            Console.WriteLine(_account.Owner + " 向账户中存款" + amount + "元，存款后的账户余额为：" + _account.Balance);
            StateCheck();
        }

        //消费
        public override void Shopping(double amount)
        {
            double newBalance = _account.Balance - amount;
            if (newBalance > 0)
            {
                _account.Balance -= amount;
                Console.WriteLine(_account.Owner + "在《访客服务》中消费" + amount + "元，账户余额：" + _account.Balance);
            }
            else
            {
                Console.WriteLine("您的账户余额不足，请充值。");
            }
            StateCheck();
        }

        //检查用户状态
        public override void StateCheck()
        {
            if (_account.Balance > 100 && _account.Balance < 1000)
            {
                //会员用户状态
                _account.State = new MemberState(_account);
            }
            else if (_account.Balance > 1000)
            {
                //贵宾用户状态
                _account.State = new VIPState(_account);
            }
        }
    }

状态模式

原文：http://www.cnblogs.com/victorchi/p/5089992.html