设计模式（十三）：组合模式

一、定义

将对象组合成树形结构以表示‘部分-整体’的层次结构。组合模式使得用户对单个对象和组合对象的使用具有一致性。

二、实例：总店—加盟店

总店和加盟店实行的会员制度一样，但是总店和加盟店又是一个层级关系。这样的关系使得形成了一张树状图。

根节点—子节点—叶子

2.1 抽象组合关系

//--------------组合-------------------
    public abstract class Company
    {
        public string ShopID { get; set; }
        public Company(string shopID)
        {
            ShopID = shopID;
        }
        public abstract void AddShop(Company shop);
        public abstract void RemoveShop(Company shop);
        public abstract void DisplayShops();        
    }

2.2 定义 节点和叶子

 //--------------节点--------------------
    public class Headquarters : Company
    {
        List<Company> shops = new List<Company>();
        public Headquarters(string shopID) : base(shopID)
        {          
        }
        public override void AddShop(Company shop)
        {
            shops.Add(shop);
        }      
        public override void RemoveShop(Company shop)
        {
            shops.Remove(shop);
        }
        public override void DisplayShops()
        {
            foreach (var shop in shops)
            {
                Console.WriteLine("展示店铺："+shop.ShopID);
            }
        }
    }

//-------------------叶子---------------------------
    public class Shop : Company
    {
        public Shop(string shopid) : base(shopid)
        {
        }        
        public override void AddShop(Company shop)
        {
            Console.WriteLine("暂无下级");
        }

        public override void DisplayShops()
        {
            throw new NotImplementedException();
        }

        public override void RemoveShop(Company shop)
        {
            Console.WriteLine("暂无下级");
        }
    }

2.3 客户端

 //---------------------组合模式------------------------
            Component.Company baseShop = new Component.Headquarters("华北区");
            baseShop.AddShop(baseShop);
            Component.Company shop_1 = new Component.Shop("加盟店:NO.1");
            baseShop.AddShop(shop_1);
            Component.Company shop_2 = new Component.Shop("加盟店：NO.2");
            baseShop.AddShop(shop_2);
            baseShop.DisplayShops();
            Console.ReadKey();

结果：

三、总结

需求中有部分和整体的关系，并且部分和整体的表达近乎一致。就可考虑使用组合模式。