装饰器模式

一、定义

装饰器模式动态地给一个对象增加一些额外的职责。就增加功能而言，装饰器模式比生成子类更为灵活。

二、UML类图

三、示例

需求：假设开一个奶茶店，奶茶种类繁多，如红豆奶茶，布丁奶茶，珍珠奶茶，红豆珍珠奶茶等，并根据不同配料计算价格，并且根据每个客户的要求，每种奶茶又可以加糖或者加冰，加糖加冰不额外收费。

通过组合+继承的方式改进，可使得饮品的扩展更灵活，同时也遵守了开闭原则。其中，组合是为了实现功能，而继承是为了约束类型，这其实就是装饰者模式。

代码：

1.Drink.cs

public abstract class Drink
    {
        public string Name { get; set; }

        public int Price { get; set; }

        public abstract string Desc { get; }

        public abstract int Cost { get; }
    }

2.Naicha.cs

public class Naicha : Drink
    {
        public Naicha()
        {
            Name = "奶茶";
            Price = 8;
        }
        public override string Desc => this.Name;
        public override int Cost => this.Price;
    }

3.Peiliao.cs

public class Peiliao:Drink
    {
        protected readonly Drink Drink;

        public Peiliao(Drink drink)
        {
            Drink = drink;
        }

        public override string Desc
        {
            get
            {
                return Drink.Desc + "+" + this.Name;
            }
        }

        public override int Cost
        {
            get
            {
                return Drink.Cost + this.Price;
            }
        }
    }

4.Hongdou.cs

public class Hongdou : Peiliao
    {
        public Hongdou(Drink drink) : base(drink)
        {
            Name = "红豆";
            Price = 1;
        }
    }

5.Program.cs

internal class Program
    {
        static void Main(string[] args)
        {
            Drink drink = new Naicha();
            drink = new Hongdou(drink);
            drink = new Bing(drink);
            drink = new Buding(drink);
            Console.WriteLine($"描述：{drink.Desc},价格:{drink.Cost}");

            Drink drink2 = new Kafei();
            drink2 = new Kafeibanlv(drink2);
            drink2 = new Tang(drink2);
            Console.WriteLine($"描述：{drink2.Desc},价格:{drink2.Cost}");
        }
    }