Chain of Responsibility -- Design Pattern

       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.

Participants

    The classes and/or objects participating in this pattern are:

• Handler(Approver)

     Defines an interface for handling the requests

     (optional) implements the successor link

• Concrete Handler(Director, Vice President, President)

      Handles requests it is responsible for

     Can access its successor

     If the Concrete Handler can handle the request, it does so; otherwise it forwards the request to its successor

• Client(Chain App)

   Initiates the request to a ConcreteHandler object on the chain

Example for Chain of Responsibility Design pattern

using System;  namespace  Chain.Structural {   /// <summary>   /// MainApp startup class for Structural   /// Chain of Responsibility Design Pattern.   /// </summary>   class MainApp   {     /// <summary>     /// Entry point into console application.     /// </summary>     static void Main()     {       // Setup Chain of Responsibility       Handler h1 = new ConcreteHandler1();       Handler h2 = new ConcreteHandler2();       Handler h3 = new ConcreteHandler3();       h1.SetSuccessor(h2);       h2.SetSuccessor(h3);        // Generate and process request       int[] requests = { 2, 5, 14, 22, 18, 3, 27, 20 };        foreach (int request in requests)       {         h1.HandleRequest(request);       }        // Wait for user       Console.ReadKey();     }   }    /// <summary>   /// The 'Handler' abstract class   /// </summary>   abstract class Handler   {     protected Handler successor;      public void SetSuccessor(Handler successor)     {       this.successor = successor;     }      public abstract void HandleRequest(int request);   }    /// <summary>   /// The 'ConcreteHandler1' class   /// </summary>   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);       }     }   }    /// <summary>   /// The 'ConcreteHandler2' class   /// </summary>   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);       }     }   }    /// <summary>   /// The 'ConcreteHandler3' class   /// </summary>   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);       }     }   } }

Output ConcreteHandler1 handled request 2 ConcreteHandler1 handled request 5 ConcreteHandler2 handled request 14 ConcreteHandler3 handled request 22 ConcreteHandler2 handled request 18 ConcreteHandler1 handled request 3 ConcreteHandler3 handled request 27 ConcreteHandler3 handled request 20