Implementación del patrón de decorador

Question

Se intentó implementar el patrón de decorador en C# a partir del código del libro "Modelos de diseño de Head First" (escrito en Java).

Estoy empezando con C# y, por lo tanto, soy nuevo en la sintaxis, por lo que no estoy seguro de por qué no puedo hacer funcionar la línea de código comentada a continuación.

Aquí es la primera clase abstracta-base y sus clases derivadas en el patrón Decorator:

using System; 

public abstract class Beverage 
{ 
    private String m_description; 

    // get a description of the beverage 
    public virtual String Description { get { return m_description; } } 

    // calculate cost of the beverage 
    public abstract double Cost(); 
} 

// HouseBlend coffee implements Beverage 
public class HouseBlend : Beverage 
{ 
    // Constructor 
    public HouseBlend() { m_description = "House Blend"; } 

    // calculate base cost of House Blend 
    public override double Cost() { return 0.89; } 
} 

// DarkRoast coffee implements Beverage 
public class DarkRoast : Beverage 
{ 
    // Constructor 
    public DarkRoast() { m_description = "Dark Roast"; } 

    // calculate base cost of Dark Roast 
    public override double Cost() { return 1.00; } 
} 

// Espresso coffee implements Beverage 
public class Espresso : Beverage 
{ 
    // Constructor 
    public Espresso() { m_description = "Espresso"; } 

    // calculate base cost of Espresso 
    public override double Cost() { return 1.99; } 
} 

El código erróneo es en el método de costo() de la clase Mocha:

using System; 

// abstract base class CondimentDecorator is-a Beverage 
public abstract class CondimentDecorator : Beverage {} 

// Mocha implements the CondimentDecorater 
public class Mocha : CondimentDecorator 
{ 
    // Condiment decorator has-a Beverage (recursion!) 
    private Beverage m_beverage; 

    // Constructor binds the object passed to member var 
    public Mocha(Beverage beverage) 
    { 
     this.m_beverage = beverage; 
    } 

    // getter implements abstract class Description 
    public override String Description 
    { 
     get 
     { 
      return m_beverage.Description + ", Mocha"; 
     } 
    } 

    // get the Cost of the condiment plus the base-cost 
    // of the original beverage 
    public new double Cost()    // ERROR: 'Mocha.Cost()' hides inherited 
    {          // member 'Beverage.Cost()' 
     return 0.20 + m_beverage.Cost(); 
    } 
} 

Answer 1

Cambie new a override. Además, m_description debe ser protected.

Answer 2

Ha declarado el método Cost() de Mocha como nuevo en lugar de anular. Vea aquí la diferencia: http://blogs.msdn.com/b/csharpfaq/archive/2004/03/12/what-s-the-difference-between-code-override-code-and-code-new-code.aspx

Answer 3

Así es como debe verse su código.

public abstract class Beverage 
{ 
    protected string m_description = "Unknown Beverage"; 

    public virtual string GetDescription() 
    { 
     return m_description; 
    } 

    public abstract double Cost(); 
} 

public abstract class CondimentDecorator : Beverage 
{ 
} 

public class Espresso : Beverage 
{ 
    public Espresso() 
    { 
     m_description = "Espresso"; 
    } 

    public override double Cost() 
    { 
     return 1.99; 
    } 
} 

public class HouseBlend : Beverage 
{ 
    public HouseBlend() 
    { 
     m_description = "House Blend Coffe"; 
    } 

    public override double Cost() 
    { 
     return 0.89; 
    } 
} 

public class DarkRoast : Beverage 
{ 
    public DarkRoast() 
    { 
     m_description = "Dark Roast"; 
    } 

    public override double Cost() 
    { 
     return 0.99; 
    } 
} 

public class Mocha : CondimentDecorator 
{ 
    Beverage beverage; 

    public Mocha(Beverage beverage) 
    { 
     this.beverage = beverage; 
    } 

    public override string GetDescription() 
    { 
     return beverage.GetDescription() + ", Mocha"; 
    } 

    public override double Cost() 
    { 
     return 0.20 + beverage.Cost(); 
    } 
} 

public class Soy : CondimentDecorator 
{ 
    Beverage beverage; 

    public Soy(Beverage beverage) 
    { 
     this.beverage = beverage; 
    } 

    public override string GetDescription() 
    { 
     return beverage.GetDescription() + ", Soy"; 
    } 

    public override double Cost() 
    { 
     return 0.15 + beverage.Cost(); 
    } 
} 

public class Whip : CondimentDecorator 
{ 
    Beverage beverage; 

    public Whip(Beverage beverage) 
    { 
     this.beverage = beverage; 
    } 

    public override string GetDescription() 
    { 
     return beverage.GetDescription() + ", Whip"; 
    } 

    public override double Cost() 
    { 
     return 0.10 + beverage.Cost(); 
    } 
}