設計模式：狀態模式

狀態模式（State）：當一個對象的內在狀態改變時允許改變其行為，這個對象看起來像時改變了其類。

namespace StateDesign
{
    public abstract class State
    {
        public abstract void Handle(Context context);
    }
    public class ConcreteStateA : State
    {
        public override void Handle(Context context)
        {
            context.State=new ConcreteStateB();
        }
    }
    public class ConcreteStateB : State
    {
        public override void Handle(Context context)
        {
            context.State = new ConcreteStateA();
        }
    }
    public class Context
    {
        private State state;
        public Context(State state)
        {
            this.state = state;
        }
        public State State
        {
            get { return state; }
            set
            {
                state = value;
                Console.WriteLine("當前狀態：" + state.GetType().Name);
            }
        }
        public void Request()
        {
            state.Handle(this);
        }
    }
}

測試代碼：

            StateDesign.Context c = new StateDesign.Context(new ConcreteStateA());
            c.Request();
            c.Request();
            c.Request();
            c.Request();