狀態模式

我們把影響物件行為的一個或多個動態變化的屬性稱為狀態，狀態模式所處理的物件是有狀態的，當然狀態復雜才能體現出模式的精髓，

簡單一點例子就是等紅路燈

namespace 狀態模式一
{
    internal class Program
    {
        static void Main(string[] args)
        {
            TrafficLight trafficLight = new TrafficLight(new GreenLightState());
            trafficLight.Show();
            trafficLight.SetState(new YellowLightState());
            trafficLight.Show();
            trafficLight.SetState(new RedLightState());
            trafficLight.Show();
        }
    }

    /// <summary>
    /// 定義狀態的抽象類
    /// </summary>
    public abstract class TrafficLighState
    {
        public abstract void Display();
    }

    #region 具體實作
    public class RedLightState : TrafficLighState
    {
        public override void Display()
        {
            Console.WriteLine("RedLight");
        }
    }
    public class GreenLightState : TrafficLighState
    {
        public override void Display()
        {
            Console.WriteLine("GreenLight");
        }
    }
    public class YellowLightState : TrafficLighState
    {
        public override void Display()
        {
            Console.WriteLine("YellowLight");
        }
    } 
    #endregion

    /// <summary>
    /// 狀態控制類
    /// </summary>
    public class TrafficLight
    {
        private TrafficLighState trafficLighState;
        public TrafficLight(TrafficLighState trafficLighState)
        {
            this.trafficLighState = trafficLighState;
        }
        public void SetState(TrafficLighState state)
        {
            trafficLighState = state;
        }
        public void Show()
        {
            trafficLighState.Display();
        }
    }
}

上面實體狀態控制類控制的是一個狀態的型別，看起來很眼熟，比如策略模式（他是通過委托來控制行為），又比如模板方法（通過繼承來控制行為），只不過這里是控制一個狀態類，

下面通過汽車的狀態舉的例子：

using System.Numerics;
using static System.Runtime.InteropServices.JavaScript.JSType;

namespace 狀態模式二
{
    internal class Program
    {
        static void Main(string[] args)
        {
            var lamborghini = new Car();

            Display(lamborghini.CurrentState);
            lamborghini.TaskAction(Action.Start);

            Display(lamborghini.CurrentState);
            lamborghini.TaskAction(Action.Start);

            Display(lamborghini.CurrentState);
            lamborghini.TaskAction(Action.Accelerate); //加速

            Display(lamborghini.CurrentState);
            lamborghini.TaskAction(Action.Stop);

            Display(lamborghini.CurrentState);
            /* result
                車輛當前狀態: Stopped
                車輛當前狀態:Started
                車輛當前狀態:Started
                車輛當前狀態:Running
                車輛當前狀態:Stopped
            */
        }
        static void Display(State state)
        {
            Console.WriteLine($"車輛當前狀態:{state}");
        }
    }
    /// <summary>
    /// 模擬汽車的狀態和駕駛員的動作判斷車輛當前的狀態
    /// </summary>
    public class Car
    {
        private State state = State.Stopped;
        public State CurrentState { get { return state; } }

        public void TaskAction(Action action)
        {
            state = (state, action) switch
            {
                (State.Stopped, Action.Start) => State.Started,
                (State.Started, Action.Accelerate) => State.Running,
                (State.Started, Action.Stop) => State.Stopped,
                (State.Running, Action.Stop) => State.Stopped,
                _ => state
            };
        }
    }
    public enum State { Stopped, Started, Running }
    public enum Action { Stop, Start, Accelerate }
}

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