রবিবার, ১৭ নভেম্বর, ২০১৩

Decorator Pattern



  • Decorator pattern structural patterns group Gi AšÍf©~³ GKwU pattern
  • GB pattern use K‡i †Kvb existing object Gi behavior alter bv K‡i  on the fly new behavior add Kiv hvq|
intent
  • Decorator pattern composition Gi gva¨‡g dynamically object G new behavior add K‡i|
  • Either same base class ‡_‡K inheriting Gi gva¨‡g wKsev shared interface implementing I class instance injecting Gi gva¨‡g decorated Kiv nq i.e. interface ‡K class constructor Øviv injecting Gi gva¨‡g Decorator pattern achieve Kiv hvq|
  • Ab¨fv‡e ejv hvq Decorator pattern n‡jv Ggb GK ai‡bi process hvi gva¨‡g existing ‡Kvb class ‡K behavior or state extend K‡i Ggb class Øviv wrapping Kiv nq|
  • Extended behavior combine Kivi Rb¨ Multiple decorators add Kiv hvq|
UMl
  • wb‡¤œi Figure Decorator  pattern Gi UML representation show K‡i|
  • Zv‡`i role mg~n wb¤œiƒct-
ü  IProduct product Gi Rb¨ defined GKwU interface
ü  DefaultProduct Ges ProductDecorator Aek¨B IProduct interface ‡K implement Ki‡e|
ü  DefaultProduct class Gi base functionality provide Ki‡e|
ü  ProductDecorator IProduct interface ‡K implement K‡i Ges IProduct instance Gi GKwU reference wb‡q injected nq| d‡j inner instance wrapped enable nq|
ü  ConcreteDecoratorA I ConcreteDecoratorA ProductDecorator ‡_‡K inherit nq Ges IProduct instance G state  Ges new behavior add K‡i|



Real Life Example
  • Painting GKwU component
  • Frame GKwU component
  • Matt GKwU component
  • Hanging Gi c~‡e© painting ‡K matted I framed Kiv nq|
  • hw`I Painting, Frame, Matt wZbwU Avjv`v Avjv`v component Z_vwc Bnv hLb †`Iqv‡j Uvbv‡bv nq ZLb Bnv single visual component wnmv‡e `k©bv_©x‡`i `„wó‡MvPi nq|
  • Abyiƒcfv‡e Decorator Pattern Gi †ÿ‡ÎI GKvwaK class Gi combination G GKwU class ‰Zix nq i.e.  GKwU class  Av‡iKwU‡K decorate K‡i wKš‘ hLb User Dnv use K‡i ZLb single class Gi b¨vq behave K‡i|


Steps For Implementation

Step 1: Create an interface.

public interface IPrice
{
   decimal Cost(decimal quantity, decimal rate);

}

Step 2: Create concrete classes implementing the same interface.

public class Price:IPrice
{
   public decimal Cost(decimal quantity, decimal rate)
   {
       return quantity * rate;
   }

}
Step 3: Create decorator classes implementing the interface as well as injecting the interface through constructor.

public class PriceWithDiscountAndVat:IPrice
{

        protected decimal _vat;
        protected decimal _discount;
        protected IPrice _price;

        public PriceWithDiscountAndVat(IPrice price, decimal vat, decimal discount)
        {
            this._price = price;
            this._discount = discount;
            this._vat = vat;
        }

        public decimal Cost(decimal quantity, decimal rate)
        {
            return (_price.Cost(quantity, rate) + _vat) - _discount;
        }

}


public class PriceWithoutDiscount:IPrice
{
         protected decimal _vat;
         protected IPrice _price;

        public PriceWithoutDiscount(IPrice price, decimal vat)
        {
            this._price = price;
            this._vat = vat;
        }

        public decimal Cost(decimal quantity, decimal rate)
        {
            return _price.Cost(quantity, rate) + _vat;
        }
}

Step 4: Call decorated classes for getting custom behavior

class Program
{
        static void Main(string[] args)
        {
            decimal quantity = 100;
            decimal rate = 20.44m;
            decimal vat = quantity*rate*0.1m;
            decimal discount = quantity*rate*0.15m;

            IPrice price = new PriceWithDiscountAndVat(new Price(), vat,quantity);

            IPrice priceWithoutDiscount = new PriceWithoutDiscount(new Price(), vat);

            Console.Write("Price With Discount = " + price.Cost(quantity, rate).ToString());
            Console.Write("\n");
            Console.Write("Price Without Discount = " + priceWithoutDiscount.Cost(quantity, rate).ToString());
            Console.ReadKey();
        }
  }
 



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