模式定义

合成(Composite)模式：将对象组合成树形结构以表示“部分-整体”的层次结构。Composite使得用户对单个对象和组合对象的使用具有一致性。

UML类图

• 抽象构件（component）： 为参加组合的对象定义出公共的接口及其默认的行为，用来管理所有的子对象。负责对整体操作的方法有：Operation() Add(Component) Remove(Component) GetChild(int)
• 树枝构件(Composite): 抽象构建子类，并包含抽象构建类型的集合（存放下级对象）。参加组合的有下级子对象的对象，除拥有Operation()外，还包括整体操作方法：Add(Component) Remove(Component) GetChild(int)。

• 树叶构件(Left)： 抽象构建子类，没有下级子对象的对象，拥有Operation()即可

  代码结构

    public static class CompositeApp{public static void Run(){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);root.Add(new Leaf("Leaf C"));root.Display(1);Console.ReadKey();}}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 Display(int depth){Console.WriteLine(new string('-', depth) + name);foreach (Component component in _children){component.Display(depth + 2);}}public override void Remove(Component c){_children.Remove(c);}}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);}}

情景案例

这里以画一副画为例，一幅画有好多元素组成，每种元素都有展示方法Display(int indent);。但有的是独立的元素（树叶节点），有的是组合元素（树枝节点）。
其实Asp.Net WebForm 中的Control就是组合机构，有个控件可以包含其它控件

public static class MainApp{public static void Run(){CompositeElement root = new CompositeElement("Picture");root.Add(new PrimitiveElement("Red Line"));root.Add(new PrimitiveElement("Blue Circle"));root.Add(new PrimitiveElement("Green Box"));CompositeElement comp = new CompositeElement("Two Circles");comp.Add(new PrimitiveElement("Black Circle"));comp.Add(new PrimitiveElement("White Circle"));root.Add(comp);PrimitiveElement pe = new PrimitiveElement("Yellow Line");root.Add(pe);root.Remove(pe);root.Display(1);Console.ReadKey();}}/// <summary>/// 画元素/// </summary>abstract class DrawingElement{protected string _name;public DrawingElement(string name){this._name = name;}public abstract void Add(DrawingElement d);public abstract void Remove(DrawingElement d);public abstract void Display(int indent);}/// <summary>/// 单独元素/// </summary>class PrimitiveElement : DrawingElement{public PrimitiveElement(string name): base(name){}public override void Add(DrawingElement c){Console.WriteLine("Cannot add to a PrimitiveElement");}public override void Remove(DrawingElement c){Console.WriteLine( "Cannot remove from a PrimitiveElement");}public override void Display(int indent){Console.WriteLine(new String('-', indent) + " " + _name);}}/// <summary>/// 组合元素/// </summary>class CompositeElement : DrawingElement{private List<DrawingElement> elements = new List<DrawingElement>();public CompositeElement(string name) : base(name){}public override void Add(DrawingElement d){elements.Add(d);}public override void Remove(DrawingElement d){elements.Remove(d);}public override void Display(int indent){Console.WriteLine(new String('-', indent) + "+ " + _name);foreach (DrawingElement d in elements){d.Display(indent + 2);}}}