UML:

通过让多个对象都有机会处理该请求,来避免耦合请求的发送者的接收器，。链接接收对象并且通过链来传递请求直到一个对象处理它。

Avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request. Chain the receiving objects and pass the request along the chain until an object handles it. 

Avoid coupling the sender of a request to its receiver by giving more than one object a chance to handle the request. Chain the receiving objects and pass the request along the chain until an object handles it. 

 

  • Handler   ()
    • defines an interface for handling the requests
    • 定义一个处理请求的接口
    • (optional) implements the successor link
    • 实现successor链接
  • ConcreteHandler   ()
    • handles requests it is responsible for
    • 处理负责的请求
    • can access its successor
    • 能够访问successor 
    • if the ConcreteHandler can handle the request, it does so; otherwise it forwards the request to its successor
    • 如果ConcreteHandler能处理请求,它也可以.
  • Client   ()
    • initiates the request to a ConcreteHandler object on the chain  
    • 启动链上的请求

 

Sample:

 

    abstract class Handler
    {
        protected Handler successor; 
        public void SetSuccessor(Handler successor)
        { 
            this.successor = successor; 
        } 
        public abstract void HandleRequest(int request); 
    }

 

 

    class ConcreteHandler1:Handler
    {
        public override void HandleRequest(int request)
        {
            if (request >= 0 && request < 10)
            { 
                Console.WriteLine("{0} handled request {1}", 
                  this.GetType().Name, request); 
            } 
            else if (successor != null)
            { 
                successor.HandleRequest(request); 
            } 
        }
    }

 

    class ConcreteHandler2:Handler
    {
        public override void HandleRequest(int request)
        {
            if (request >= 10 && request < 20)
            { 
                Console.WriteLine("{0} handled request {1}", 
                  this.GetType().Name, request); 
            } 
            else if (successor != null)
            { 
                successor.HandleRequest(request); 
            } 
        }
    }

 

    class ConcreteHandler3:Handler
    {
        public override void HandleRequest(int request)
        {
            if (request >= 20 && request < 30)
            { 
                Console.WriteLine("{0} handled request {1}", 
                  this.GetType().Name, request); 
            } 
            else if (successor != null)
            {
                successor.HandleRequest(request); 
            } 
        }
    }

 

            #region ChainOR
            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); 
            } 
            #endregion