状态模式

允许一个对象在其内部状态改变时自动改变其行为，对象看起来就像是改变了它的类

public class User
{
    public State State { get; set; }
    public string Name { get; set; }
    public User(string name)
    {
        Name = name;
        State = new Vip1(this, 0);
    }
    // 充钱
    public void Recharge(double count)
    {
        State.Recharge(count);
        Console.WriteLine("充值金额为:{0}", count);
        Console.WriteLine("用户余额为:{0}", State.Money);
        Console.WriteLine("用状态为:{0}", State.GetType().Name);
    }
}
// 抽象状态类
public abstract class State
{
    public User User { get; set; }
    public double UpperLimit { get; set; }
    public double Money { get; set; }
    /// <summary>
    /// 充钱
    /// </summary>
    /// <param name="count"></param>
    public virtual void Recharge(double count)
    {
        Money += count;
    }
}
public class Vip1 : State
{
    public Vip1(User user, double money)
    {
        User = user;
        Money = money;
        UpperLimit = 100;
    }
    public override void Recharge(double count)
    {
        base.Recharge(count);
        if (Money > UpperLimit)
        {
            User.State = new Vip2(this);
        }
    }
}
public class Vip2 : State
{
    public Vip2(State state)
    {
        User = state.User;
        Money = state.Money;
        UpperLimit = 300;
    }
    public override void Recharge(double count)
    {
        base.Recharge(count);
        if (Money > UpperLimit)
        {
            User.State = new Vip3(this);
        }
    }
}
public class Vip3 : State
{
    public Vip3(State state)
    {
        User = state.User;
        Money = state.Money;
        UpperLimit = 700;
    }
    public override void Recharge(double count)
    {
        base.Recharge(count);
        if (Money > UpperLimit)
        {
            Console.WriteLine("没有更高级别了");
        }
    }
}

调用：

var user = new User("admin");
for (var j = 0; j < 10; j++)
{
    user.Recharge(20 * j);
}

reference

C#设计模式之十八状态模式（State Pattern）【行为型】

C#设计模式(19)——状态者模式（State Pattern）