帮忙看看错在哪里...希望能详细解答一下...

[TimLeaf]

head first 设计模式这本书...
练习装饰者模式代码的时候，出现了问题...希望大家帮忙看一下...
这是类图：

以下是我的代码：
Beverage.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace DecoratorPattern
{
	public abstract class Beverage
	{
		private String _description;
		public String Description
		{
			set { _description = value; }
			get { return _description; }
		}

		public abstract Single Cost();
	}
}

CondimentDecorate.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace DecoratorPattern
{
	public abstract class CondimentDecorate : Beverage
	{
		public override Single Cost()
		{
			return 0.0f;
		}
	}
}

DarkRoast.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace DecoratorPattern
{
	public class DarkRoast : Beverage
	{
		public DarkRoast()
		{
			Description = "Dark Roast Coffee";
		}

		public override Single Cost()
		{
			return 0.99f;
		}
	}
}

Decaf.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace DecoratorPattern
{
	public class Decaf : Beverage
	{
		public Decaf()
		{
			Description = "Decaf";
		}

		public override Single Cost()
		{
			return 1.05f;
		}
	}
}

Espresso.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace DecoratorPattern
{
	public class Espresso : Beverage
	{
		public Espresso()
		{
			Description = "Espresso";
		}

		public override Single Cost()
		{
			return 1.99f;
		}
	}
}

HouseBlend.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace DecoratorPattern
{
	public class HouseBlend : Beverage
	{
		public HouseBlend()
		{
			Description = "House Blend Coffee";
		}

		public override Single Cost()
		{
			return 0.89f;
		}
	}
}

Milk.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace DecoratorPattern
{
	public class Milk : CondimentDecorate
	{
		private Beverage _beverage;

		public Milk(Beverage beverage)
		{
			_beverage = beverage;
			_beverage.Description = _beverage.Description + ", Milk";
		}

		public override Single Cost()
		{
			return _beverage.Cost() + 0.10f;
		}
	}
}

Mocha.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace DecoratorPattern
{
	public class Mocha : CondimentDecorate
	{
		private Beverage _beverage;

		public Mocha(Beverage beverage)
		{
			_beverage = beverage;
			_beverage.Description = _beverage.Description + ", Mocha";
		}

		public override Single Cost()
		{
			return _beverage.Cost() + 0.2f;
		}
	}
}

Soy.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace DecoratorPattern
{
	public class Soy : CondimentDecorate
	{
		private Beverage _beverage;

		public Soy(Beverage beverage)
		{
			_beverage = beverage;
			_beverage.Description = _beverage.Description + ", Soy";
		}

		public override Single Cost()
		{
			return _beverage.Cost() + 0.15f;
		}
	}
}

以下是测试类：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace DecoratorPattern
{
	class Program
	{
		static void Main(string[] args)
		{
			Beverage beverage1 = new HouseBlend();
			Console.WriteLine(beverage1.Description + "$" + beverage1.Cost());

			Beverage beverage2 = new Espresso();
			beverage2 = new Soy(beverage2);
			beverage2 = new Mocha(beverage2);
			beverage2 = new Milk(beverage2);
			Console.WriteLine(beverage2.Description + "$" + beverage2.Cost());

			Beverage beverage3 = new DarkRoast();
			beverage3 = new Milk(beverage3);
			Console.WriteLine(beverage3.Description + "$" + beverage3.Cost());
			beverage3 = new Milk(beverage3);
			Console.WriteLine(beverage3.Description + "$" + beverage3.Cost());
			beverage3 = new Milk(beverage3);
			Console.WriteLine(beverage3.Description + "$" + beverage3.Cost());

			Console.ReadKey();
		}
	}
}

在执行到beverage2 = new Mocha(beverage2);
beverage2.Description 的值就是null...

[JeffrySun]

beverage2 = new Soy(beverage2);


这句有问题， 浏览了一眼lz的代码， 发现类继承层次上来说， 这个new有点问题，lz再开看

[TimLeaf]

那继续上图...
这是书上的部分代码...

[TimLeaf]

[claymore1114]

花眼了 先UP

[ws_hgo]

关注...

[king19840811]

mark

[空心兜兜]

被图吸引了...

[perisonchen]

标记记号，回家慢慢看...

[pbmlly]

眼花缭乱.......

[tigerleq]

Beverage beverage2 = new Espresso();
没有Description
这个属性
当然为空3

[tigerleq]

日他的
看昏了

[step_123]

关注

[rightyeah]

路过

[erytbc]

yun

[lyymax]

beverage2 = new Mocha(beverage2);
[1] [2]
这里面2号的beverage其实是Soy类型的。
所以在new Mocha()里面的代码其实是操所Soy::Description；
而你Soy的构造函数只是在操作别人的Description，并没有对自己的Description进行初始化。

[泡面之夏]

关注，UP

[悔说话的哑巴]

好多哦。。。

[readfuture]

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