装饰图案实现

问题描述

我刚刚开始使用C＃中的装饰器模式，在头像设计模式书中C＃，因此仍然是新的语法，所以我不知道为什么我无法获得下面的代码行的注释。

这是第一个抽象-base类及其派生类在Decorator模式中：

  using System; 
 
 public abstract class Beverage 
 {
 private String m_description; 
 
 //获取饮料的描述
 public virtual String Description {get {return m_description; 
 
 //计算饮料的成本
 public abstract double Cost（）; 
} 
 
 // HouseBlend咖啡器具饮料
 public class HouseBlend：饮料
 {
 //构造函数
 public HouseBlend（）{m_description =House Blend; 
 
 //计算House Blend的基本费用
 public override double Cost（）{return 0.89; 
} 
 
 // DarkRoast咖啡器具饮料
 public class DarkRoast：饮料
 {
 //构造函数
 public DarkRoast（）{ m_description =黑暗烤 
 
 //计算Dark Roast的基本费用
 public override double Cost（）{return 1.00; 
} 
 
 // Espresso咖啡器具饮料
 public class Espresso：饮料
 {
 //构造函数
 public Espresso（）{ m_description =Espresso; 
 
 //计算Espresso的基本费用
 public override double Cost（）{return 1.99; 
} 
  

违规代码位于Mocha类的Cost（）方法中：

  using System; 
 
 //抽象基类CondimentDecorator is-a Beverage 
 public abstract class CondimentDecorator：Beverage {} 
 
 // Mocha实现CondimentDecorater 
 public class Mocha：CondimentDecorator 
 {
 //调味品装饰器有一个饮料（递归！）
私人饮料m_beverage; 
 
 //构造函数绑定传递给成员的对象var 
 public Mocha（饮料饮料）
 {
 this.m_beverage = drinks; 
} 
 
 // getter实现抽象类描述
 public override String描述
 {
 get 
 {
 return m_beverage。说明+，摩卡; 
} 
} 
 
 //获取调味品的成本加上原始饮料的基本费用
 // 
 public new double成本（ ）// ERROR：'Mocha.Cost（）'隐藏继承
 {// member'Beverage.Cost（）'
 return 0.20 + m_beverage.Cost（）; 
} 
} 
  

解决方案

更改 new to override 。另外， m_description 应该是 protected 。

Trying to implement the decorator pattern in C# from the code in the "Head First Design Patterns" book (written in Java).

I am just starting out with C# and am therefore still new to the syntax, so I am not sure why I can't get the commented line of code below to work.

Here is the first abstract-base class and its derived classes in the Decorator pattern:

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; }
}

The offending code is in the Cost() method of the Mocha class:

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();
    }
}

解决方案

Change new to override. Also, m_description should be protected.

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