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();

             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 + );
             }
         }
     }

     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);
         }
     }
 }

Composite

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。