c# - 装饰者模式的实现

Question

尝试从“Head First Design Patterns”一书中的代码(用 Java 编写)在 C# 中实现装饰器模式。

我刚开始使用 C#，因此对语法还是陌生的，所以我不确定为什么我不能让下面的注释代码行工作。

这是装饰器模式中的第一个抽象基类及其派生类:

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; }
}

违规代码在 Mocha 类的 Cost() 方法中:

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

将 new 更改为 override。此外，m_description 应该是 protected。