GoF——组合模式

组合模式：将对象组合成树形结构以表示“部分-真题”的结构层次。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。

结构图：

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

namespace 组合模式
{
    class Program
    {
        static void Main(string[] args)
        {
            Composite root = new Composite("root");
            root.Add(new Leaf("Leaf A"));
            root.Add(new Leaf("Leaf B"));

            Composite comp = new Composite("Composite X");
            comp.Add(new Leaf("Leaf XA"));
            comp.Add(new Leaf("Leaf XB"));

            root.Add(comp);

            Composite comp2 = new Composite("Composite XY");
            comp2.Add(new Leaf("Leaf XYA"));
            comp2.Add(new Leaf("Leaf XYB"));

            comp.Add(comp2);

            root.Add(new Leaf("Leaf C"));

            Leaf leaf = new Leaf("Leaf D");
            root.Add(leaf);
            root.Remove(leaf);

            root.Display(1);

            Console.Read();
        }
    }

    abstract class Component
    {
        protected string name;

        public Component(string name)
        {
            this.name = name;
        }

        public abstract void Add(Component c);
        public abstract void Remove(Component c);
        public abstract void Display(int depth);
    }

    class Composite : Component
    {
        private List<Component> children = new List<Component>();

        public Composite(string name)
            : base(name)
        { }

        public override void Add(Component c)
        {
            children.Add(c);
        }

        public override void Remove(Component c)
        {
            children.Remove(c);
        }

        public override void Display(int depth)
        {
            Console.WriteLine(new String('-', depth) + name);

            foreach (Component component in children)
            {
                component.Display(depth + 2);
            }
        }
    }

    class Leaf : Component
    {
        public Leaf(string name)
            : base(name)
        { }

        public override void Add(Component c)
        {
            Console.WriteLine("Cannot add to a leaf");
        }

        public override void Remove(Component c)
        {
            Console.WriteLine("Cannot remove from a leaf");
        }

        public override void Display(int depth)
        {
            Console.WriteLine(new String('-', depth) + name);
        }
    }
}

当你发现需求中是体现部分与整体的结构时，以及你希望用户可以忽略组合对象与单个对象的不同，统一地使用组合结构中的多有对象时，就应该考虑用组合模式。