Decorator Pattern can be used to add new functionality to an
object at runtime. Decorator pattern falls under structural pattern of GOF
(Gang of Four) patterns.
When to use –
Decorator pattern can be used when you want to extend or add any additional functionality to an object at run-time. This means user will decide or select some functionality which will be added to object dynamically. The main
benefit of decorator pattern is that the existing class is not modified directly by adding any functionality to object.
There are so many real world example of Decorator pattern available but in this article I would like to explain very simple and easy real life example of Decorator pattern. Now a days mobile devices are very common and anyone can buy any mobile device of any brand. You have also observed that some companies bring some attractive offers on festival time or on some special
events. So in such offers companies are offering mobile devices at an attractive
discount and also provides some freebies like Flip Cover, Bluetooth headset etc with mobile device. So in this example you can consider mobile device as original product and different offers as decorator of original product. Let's have a look on below example how we can implement this example with decorator pattern.
Major components of Decorator Pattern –
Component – This is an interface and contains members
which is implemented by Concrete Component. Additional functionality to this
type of object will be added dynamically.
Concrete Component – This is a class and implements
Component interface.
Decorator – This is an abstract class which
implements Component interface. This class also contains additional functionalities of
decorator to be added dynamically to Component object.
Concrete Decorator – This is a class and inherits
from Decorator abstract class.
Code –
//Component
public interface IMobile
{
string ModelName();
string CompanyName();
double Price();
}
//ConcreteComponent
public class LG : IMobile
{
public string
CompanyName()
{
return "LG";
}
public string
ModelName()
{
return "LG
G Pro2";
}
public double Price()
{
return 25000;
}
public override string
ToString()
{
return string.Format("Company
: {0}, Model : {1}, Price : {2}", CompanyName(), ModelName(),
Price());
}
}
//ConcreteComponent
public class SAMSUNG : IMobile
{
public string
CompanyName()
{
return "Samsung";
}
public string
ModelName()
{
return "Galaxy
Note 5";
}
public double Price()
{
return 30000;
}
public override string
ToString()
{
return string.Format("Company
: {0}, Model : {1}, Price : {2}", CompanyName(), ModelName(),
Price());
}
}
//Decorator
public class OffersDecorator : IMobile
{
protected IMobile
iMobile;
public OffersDecorator(IMobile mobile)
{
iMobile = mobile;
}
public virtual string
CompanyName()
{
return
iMobile.CompanyName();
}
public virtual string
ModelName()
{
return
iMobile.ModelName();
}
public virtual double Price()
{
return iMobile.Price();
}
public virtual double
Discount { get; set; }
public virtual string
OfferName { get; set; }
public virtual string
Accessories { get; set; }
}
//ConcreteDecorator
public class DiwaliOffersDecorator : OffersDecorator
{
public
DiwaliOffersDecorator(IMobile mobile) : base(mobile)
{
}
public override string
CompanyName()
{
return
iMobile.CompanyName();
}
public override string
ModelName()
{
return
iMobile.ModelName();
}
public override double Price()
{
return (iMobile.Price()-
(iMobile.Price() * (Discount/100)));
}
public override string
ToString()
{
return string.Format("Offer
Applicable : {0}, Discount : {1}%,\nAdditional Accessories : {2},\nCompany :
{3}, Model : {4}, Discounted Price : {5}", OfferName,
Discount, Accessories, CompanyName(), ModelName(), Price());
}
}
//ConcreteDecorator
public class SpecialOffersDecorator : OffersDecorator
{
public
SpecialOffersDecorator(IMobile mobile) : base(mobile)
{
}
public override string
CompanyName()
{
return
iMobile.CompanyName();
}
public override string
ModelName()
{
return
iMobile.ModelName();
}
public override double Price()
{
return (iMobile.Price() -
(iMobile.Price() * (Discount / 100)));
}
public override string
ToString()
{
return string.Format("Offer
Applicable : {0}, Discount : {1}%,\nAdditional Accessories : {2},\nCompany :
{3}, Model : {4}, Discounted Price : {5}", OfferName,
Discount, Accessories, CompanyName(), ModelName(), Price());
}
}
//Client
class Program
{
static void Main(string[] args)
{
//creating original product
LG
LgMobile = new LG();
Console.WriteLine("Original
Product");
Console.WriteLine(LgMobile.ToString());
Console.WriteLine("");
//adding additional functionalities
to original product via decorator
DiwaliOffersDecorator
diwaliOffers = new DiwaliOffersDecorator(LgMobile);
diwaliOffers.Discount = 25;
diwaliOffers.OfferName = "Diwali
Bonanza Offer";
diwaliOffers.Accessories = "Flip
Cover";
Console.WriteLine(diwaliOffers.ToString());
Console.WriteLine("-".PadLeft(50,'-'));
//creating original product
SAMSUNG
samsungMobile = new SAMSUNG();
Console.WriteLine("Original
Product");
Console.WriteLine(samsungMobile.ToString());
Console.WriteLine("");
//adding additional functionalities
to original product via decorator
SpecialOffersDecorator
specialOffers = new SpecialOffersDecorator(samsungMobile);
specialOffers.Discount = 10;
specialOffers.OfferName = "Special
Offer";
specialOffers.Accessories = "Bluetooth
Headset";
Console.WriteLine(specialOffers.ToString());
Console.ReadLine();
}
}
Output –
As you can see in above example, LG and Samsung mobile
manufacturer has their mobile devices available in market and they want to sell
them on different occasions with different offers like festival offer or some special offer but the original
product will be the same. So the discount and additional accessories will be different based on offer and can be consider as a decorator of product. They want to keep repeating such offers multiple times in a year on different occasions. So you can attach any decorator with any mobile device based on offer. In above example, you can add as many
mobile devices you want and also you can attach any mobile device with any
offer (decorator) dynamically.
I hope you enjoy reading this article and helps you to know more about Decorator
Pattern. Please leave your feedback in comments section below.
References –
See Also –
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Creational Patterns
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Structural Patterns
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Behavioral Patterns
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