Decorator Design Pattern

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In this video we will learn

• What is Decorator Design Pattern
• Implementation guidelines of decorator design pattern
• Simple Decorator Design Pattern example

Decorator Design Pattern : As per the GOF definition, decorator Pattern states that we need to “Attach additional responsibilities to an object dynamically. Decorators provide A flexible alternative to sub classing for extending functionality.”

This pattern Falls under the category of Structural Design Pattern and is also known as Wrapper.


Implementation Guidelines : We need to use Decorator Design Pattern when 

• We need to add responsibilities to individual objects dynamically and transparently,  
• The extension by sub classing is impractical.  
• Class definition may be hidden or otherwise unavailable for sub classing.  

Representation Diagram

• Client : Clients use the Component interface to interact with objects
• Component : Defines the interface for objects that can have responsibilities added to them dynamically.
• ConcreteComponent : Defines an object to which additional responsibilities can be attached.
• Decorator : Maintains a reference to a Component object and defines an interface that conforms to Component's interface.
• ConcreteDecorator : Adds responsibilities to the component.

Let’s start building our code with Decorator design pattern implementation.

Step 1 : Add Interface ICar

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

namespace DecoratorDemo.Component

{

    public interface ICar

    {

        string Make { get; }

        double GetPrice();

    }

}

Step 2 : Create Concrete component Hyndai to implement ICar

using DecoratorDemo.Component;

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

namespace DecoratorDemo.ConcreteComponent

{

    public sealed class Hyndai : ICar

    {

        public string Make

        {

            get { return "HatchBack"; }

        }

        public double GetPrice()

        {

            return 800000;

        }

    }

}

Step 3 : Create Concrete component Suzuki to implement ICar

using DecoratorDemo.Component;

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

namespace DecoratorDemo.ConcreteComponent

{

    public sealed class Suzuki : ICar

    {

        public string Make

        {

            get { return "Sedan"; }

        }

        public double GetPrice()

        {

            return 1000000;

        }

    }

}

Step 4 : Create Decorator Class CarDecorator to decorate the Icar using CarDecorator

using DecoratorDemo.Component;

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

namespace DecoratorDemo.Decorator

{

    public abstract class CarDecorator : ICar

    {

        private ICar car;

        public CarDecorator(ICar Car)

        {

            car = Car;

        }

        public string Make { get { return car.Make; } }

        public double GetPrice()

        {

            return car.GetPrice();

        }

        public abstract double GetDiscountedPrice();

    }   

}

Step 5 : Create Concrete Decorator OfferPrice to decorate the Icar using CarDecorator

using DecoratorDemo.Component;

using DecoratorDemo.Decorator;

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

namespace DecoratorDemo.ConcreteDecorator

{

    public class OfferPrice : CarDecorator

    {

        public OfferPrice(ICar car) : base(car)

        {

        }

        public override double GetDiscountedPrice()

        {

            return .8 * base.GetPrice();

        }

    }

}

Step 6 : Use the car decorator in the main program to achieve the output

using DecoratorDemo.Component;

using DecoratorDemo.ConcreteComponent;

using DecoratorDemo.ConcreteDecorator;

using DecoratorDemo.Decorator;

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

namespace DecoratorDemo

{

    class Program

    {

        static void Main(string[] args)

        {

            ICar car = new Suzuki();

            CarDecorator decorator = new OfferPrice(car);

            Console.WriteLine(string.Format("Make :{0}  Price:{1} " +

                "DiscountPrice : {2}"

                , decorator.Make,  decorator.GetPrice().ToString(),

                decorator.GetDiscountedPrice().ToString()));         

            Console.ReadLine();

        }

    }   

}

Step 7 : Run the application to see the expected output

Make : Sedan Price:1000000 DiscountPrice: 800000

Step 8 : Above mentioned classes are created under the below folder structure. Again it’s not mandatory to follow this folder structure as we are just doing this for representation purpose.