Chain of Responsibility 设计模式

将对事物处理的责任者对象组成一个链，当一个事物要处理的时候，根据事物的属性，能对该事物处理的责任者将事物接受并处理，不能处理的时候，将该对象传递下去，直到遍历所有的责任者。
对公司内采购这个事物，需要主管 或副总裁或总裁的批准，1万元以下的可由主管批准，超过1万的需要由副总裁批准，超过25000的需要由总裁批准。对这个例子，用程序实现如下：

   /// Chain of Responsibility 设计模式.
    class MainApp
    {
        static void Main()
        {

            //建立责任者链
            Approver larry = new Director();//主管
            Approver sam = new VicePresident();//副总裁
            Approver tammy = new President();//总裁
            larry.SetSuccessor(sam);//设置主管的上级：副总裁
            sam.SetSuccessor(tammy);//设置副总裁的上级总裁。

            // 创建购买对象
            Purchase p = new Purchase(2034, 350.00, "Supplies");
            //将购买对象递交责任链上的主管
            larry.ProcessRequest(p);

            p = new Purchase(2035, 32590.10, "Project X");
            larry.ProcessRequest(p);

            p = new Purchase(2036, 122100.00, "Project Y");
            larry.ProcessRequest(p);

            Console.ReadKey();
        }
    }

    //责任者(Handler)的抽象基类。
    abstract class Approver
    {
        protected Approver successor;
        //设置自己的上级
        public void SetSuccessor(Approver successor)
        {
            this.successor = successor;
        }
        //批准的处理
        public abstract void ProcessRequest(Purchase purchase);
    }
    //主管类。
    class Director : Approver
    {
        public override void ProcessRequest(Purchase purchase)
        {
            //购买对象小于10000时，可批准。
            if (purchase.Amount < 10000.0)
            {

                Console.WriteLine("{0} approved request# {1}",

                  this.GetType().Name, purchase.Number);

            }
            else if (successor != null)//超过1万让上级处理
            {

                successor.ProcessRequest(purchase);

            }
        }
    }
    //副总裁类
    class VicePresident : Approver
    {
        public override void ProcessRequest(Purchase purchase)
        {
            //购买对象小于25000时，可批准。
            if (purchase.Amount < 25000.0)
            {
                Console.WriteLine("{0} approved request# {1}",
                  this.GetType().Name, purchase.Number);
            }
            else if (successor != null)//超过25000时让上级处理。
            {
                successor.ProcessRequest(purchase);
            }
        }
    }
    //总裁类
    class President : Approver
    {
        public override void ProcessRequest(Purchase purchase)
        {
            //购买对象小于10万时可批准。
            if (purchase.Amount < 100000.0)
            {
                Console.WriteLine("{0} approved request# {1}",
                this.GetType().Name, purchase.Number);
            }
            else//超过10万的购买对象须开会研究决定。
            {
                Console.WriteLine(
                  "Request# {0} requires an executive meeting!", purchase.Number);
            }
        }
    }
    //购买对象类。
    class Purchase
    {
        private int _number;
        private double _amount;
        private string _purpose;

        // Constructor
        public Purchase(int number, double amount, string purpose)
        {
            this._number = number;
            this._amount = amount;
            this._purpose = purpose;
        }
        // Gets or sets purchase number

        public int Number
        {
            get { return _number; }
            set { _number = value; }
        }
        // Gets or sets purchase amount
        public double Amount
        {
            get { return _amount; }
            set { _amount = value; }
        }

        // Gets or sets purchase purpose
        public string Purpose
        {
            get { return _purpose; }
            set { _purpose = value; }
        }
    }

执行结果如下:
Director approved request# 2034
President approved request# 2035
Request# 2036 requires an executive meeting!