Decorator Design Pattern

This short article shows you how to build Decorator Design Pattern in C#.

Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality as defined by http://www.dofactory.com/net/design-patterns.

The logical diagram of Decorator Design Pattern as follow.

 decorator

First you create a Component Abstract class. This class is to define the interface for objects that can have responsibilities added to them dynamically.

  abstract class Component

  {

    public abstract void Operation();

  }

Then, create ConcreteComponent. It defines an object to which additional responsibilities can be attached.

  class ConcreteComponent : Component

  {

    public override void Operation()

    {

      Console.WriteLine(“ConcreteComponent.Operation()”);

    }

  }

Define Decorator class. This class actually derived from Component. This class maintains a reference to a Component object and defines an interface that conforms to Component’s interface.

  abstract class Decorator : Component

  {

    protected Component component;

 

    public void SetComponent(Component component)

    {

      this.component = component;

    }

 

    public override void Operation()

    {

      if (component != null)

      {

        component.Operation();

      }

    }

  }

Finally create 2 Concrete Decorator class derived again from Decorator class. It adds responsibilities to the component.

  class ConcreteDecoratorA : Decorator

  {

    public override void Operation()

    {

      base.Operation();

      Console.WriteLine(“ConcreteDecoratorA.Operation()”);

    }

  }

 

  class ConcreteDecoratorB : Decorator

  {

    public override void Operation()

    {

      base.Operation();

      AddedBehavior();

      Console.WriteLine(“ConcreteDecoratorB.Operation()”);

    }

 

    void AddedBehavior()

    {

    }

  }

This main program as below.

    static void Main()

    {

      // Create ConcreteComponent and two Decorators

      ConcreteComponent c = new ConcreteComponent();

      ConcreteDecoratorA d1 = new ConcreteDecoratorA();

      ConcreteDecoratorB d2 = new ConcreteDecoratorB();

 

      // Link decorators

      d1.SetComponent(c);

      d2.SetComponent(d1);

 

      d2.Operation();

 

      // Wait for user

      Console.ReadKey();

    }

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About chanmingman

Since March 2011 Microsoft Live Spaces migrated to Wordpress (http://www.pcworld.com/article/206455/Microsoft_Live_Spaces_Moves_to_WordPress_An_FAQ.html) till now, I have is over 1 million viewers. This blog is about more than 50% telling you how to resolve error messages, especial for Microsoft products. The blog also has a lot of guidance teaching you how to get stated certain Microsoft technologies. The blog also uses as a help to keep my memory. The blog is never meant to give people consulting services or silver bullet solutions. It is a contribution to the community. Thanks for your support over the years. Ming Man is Microsoft MVP since year 2006. He is a software development manager for a multinational company. With 25 years of experience in the IT field, he has developed system using Clipper, COBOL, VB5, VB6, VB.NET, Java and C #. He has been using Visual Studio (.NET) since the Beta back in year 2000. He and the team have developed many projects using .NET platform such as SCM, and HR based applications. He is familiar with the N-Tier design of business application and is also an expert with database experience in MS SQL, Oracle and AS 400.
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