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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

decorator design pattern implementation
  • 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.

decorator design pattern implementation c#

Design Patterns tutorial for beginners

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