C# 状态模式（State）

理解：当对象有多个状态时，把每个状态的行为写到各自的状态类里面去，当切换状态时，调用的行为也就自动切换了。 和策略模式很像，不过策略是针对外部的，而状态是针对内部的

代码：

 using System.Windows.Forms; 
namespace DesignMode.State
{

    //对象类
    public class Computer
    {
        //系统要求
        private string _request;
        public string Request
        {
            get { return _request; }
            set { _request = value; }
        }


        private OperatingSystem _os;
        public OperatingSystem OS
        {
            get { return _os; }
            set { _os = value; }
        }

        public Computer(OperatingSystem os)
        {
            this._os = os;
        }

        public void Run()
        {
            //先改状态，再执行状态对应的行为
            _os.ChangeOS(this);
            _os.Run();
        }
    }

    //抽象的对象状态类
    public abstract class OperatingSystem
    {
        public abstract void ChangeOS(Computer computer);

        public abstract void Run();
    }

    public class Vista : OperatingSystem
    {
        //子状态根据对象的系统要求属性来更改对应的状态
        public override void ChangeOS(Computer computer)
        {
            if (computer.Request.Equals("W"))
            {
                computer.OS = new Windows();
            }
            else if (computer.Request.Equals("L"))
            {
                computer.OS = new Linux();
            }
        }

        public override void Run()
        {
            MessageBox.Show("运行Vista系统");
        }
    }

    public class Windows : OperatingSystem
    {
        public override void ChangeOS(Computer computer)
        {
            if (computer.Request.Equals("V"))
            {
                computer.OS = new Vista();
            }
            else if (computer.Request.Equals("L"))
            {
                computer.OS = new Linux();
            }
        }

        public override void Run()
        {
            MessageBox.Show("运行Windows系统");
        }
    }

    public class Linux : OperatingSystem
    {
        public override void ChangeOS(Computer computer)
        {
            if (computer.Request.Equals("W"))
            {
                computer.OS = new Windows();
            }
            else if (computer.Request.Equals("V"))
            {
                computer.OS = new Vista();
            }
        }

        public override void Run()
        {
            MessageBox.Show("运行Linux系统");
        }
    }
}

客户端代码：

      

   private void btn_State_Click(object sender, EventArgs e)  

       {
            DesignMode.State.OperatingSystem os = new Windows();
            Computer computer = new Computer(os);
            computer.Request = "W";
            computer.Run();
            computer.Request = "L";
            computer.Run();
            computer.Request = "V";
            computer.Run();
        }