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Programming - Chain of Responsibility Behavioral Design Pattern

• Handlerand
  and
  • defines an interface for handling the requests
  • (optional) implements the successor link
• ConcreteHandlerand
  and
  • handles requests it is responsible for
  • can access its successor
  • if the ConcreteHandler can handle the request, it does so; otherwise it forwards the request to its successor
• Clientand
  and
  • initiates the request to a ConcreteHandler object on the chain

System;

namespace DoFactory.GangOfFour.Chain.Structural
{
// MainApp test application

class MainApp
{
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.Read();
}
}

// "Handler"

abstract class Handler
{
protected Handler successor;

public void SetSuccessor(Handler successor)
{
this.successor = successor;
}

public abstract void HandleRequest(int request);
}

// "ConcreteHandler1"

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);
}
}
}

// "ConcreteHandler2"

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);
}
}
}

// "ConcreteHandler3"

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);
}
}
}
}






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