设计模式：职责链模式

职责链模式（Chain of Responsibility）：使多个对象都有机会处理请求，从而避免请求的发送者和接受者之间的耦合关系。将这个对象连成一条链，并沿着这条链传递该请求，直到有一个对象处理它为止。

namespace ChainDesign
{
    public abstract class Handler
    {
        protected Handler successor;
        public void SetSuccessor(Handler successor)
        {
            this.successor = successor;
        }
        public abstract void HandleRequest(int request);
    }
    public class ConcreteHandler1 : Handler
    {
        public override void HandleRequest(int request)
        {
            if(request>=0&&request<10)
            {
                Console.WriteLine("{0}处理请求{1}", this.GetType().Name, request);
            }
            else if(successor!=null)
            {
                successor.HandleRequest(request);
            }
        }
    }
    public class ConcreteHandler2 : Handler
    {
        public override void HandleRequest(int request)
        {
            if (request >= 10 && request < 20)
            {
                Console.WriteLine("{0}处理请求{1}", this.GetType().Name, request);
            }
            else if (successor != null)
            {
                successor.HandleRequest(request);
            }
        }
    }
    public class ConcreteHandler3 : Handler
    {
        public override void HandleRequest(int request)
        {
            if (request >= 20 && request < 30)
            {
                Console.WriteLine("{0}处理请求{1}", this.GetType().Name, request);
            }
            else if (successor != null)
            {
                successor.HandleRequest(request);
            }
        }
    }
}

测试代码：

            Handler h1 = new ConcreteHandler1();
            Handler h2 = new ConcreteHandler2();
            Handler h3 = new ConcreteHandler3();
            h1.SetSuccessor(h2);
            h2.SetSuccessor(h3);
            int[] requests = { 2, 5, 14, 22, 18, 3, 27, 20 };
            foreach(int request in requests)
            {
                h1.HandleRequest(request);
            }