Sql server, .net and c# video tutorial: 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

(追記) (追記ここまで)
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.

(追記) (追記ここまで)
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

{

publicinterfaceICar

{

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

{

publicsealedclassHyndai : ICar

{

publicstring Make

{

get { return"HatchBack"; }

}

publicdouble 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

{

publicsealedclassSuzuki : ICar

{

publicstring Make

{

get { return"Sedan"; }

}

publicdouble 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

{

publicabstractclassCarDecorator : ICar

{

private ICar car;

public CarDecorator(ICar Car)

{

car = Car;

}

publicstring Make { get { return car.Make; } }

publicdouble GetPrice()

{

return car.GetPrice();

}

publicabstractdouble 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

{

publicclassOfferPrice : CarDecorator

{

public OfferPrice(ICar car) : base(car)

{

}

publicoverridedouble 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

{

classProgram

{

staticvoid 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

Sql server, .net and c# video tutorial

Decorator Design Pattern

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