C# 设计模式--合成模式(Composite)
Composite模式定义了单个对象和组合对象的类层次结构。(1)单个对象组合成复杂的组合对象，而多个组合对象又可以被组合成一个新的组合对象。其中，一个组合对象中的某些对象可能包容了其他对象。某些对象则表现单个基本对象，称为叶对象；某些对象代表一组对象，称为枝对象。叶对象可以组合成复杂的枝对象，而枝对象又可以被组合成新的枝对象，可以不断组合下去。
Composite模式使用户对单个对象和组合对象的使用具有一致性。客户可以一致地使用组合结构和单个对象，而不用关心处理的是一个叶节点还是一个组合组件。Composite关键是一个抽象类，这个类既可以代表一个对象，也可以代表一个容器来包含一组对象。(1)那么。Composite关键两个思想：
一、一个Composite对象既可包容Leaf对象，也可以其他包容Composite对象。
二、一个Leaf类和一个Composite共享一个在抽象类中定义的公共接口Component。(2)
在以下情况下考虑使用合成模式:
(1)表示对象的部分和整体层次结构
(2)忽略枝对象和叶对象的不同，用户同意使用组合结构的所有对象。
结构图如下：
合成模式的实现根据公共接口Component的区别分为两种形式，分别称为安全模式和透明模式。
透明模式：
公共接口Component中里面声明所有的用来管理子类对象的方法，包括Add()、Remove()，以及GetChild()方法。这样所有的叶对象和枝对象都有相同的接口，那么客户端可以将叶对象和枝对象同等对待而不用区分。
示例代码如下：
using
System;
using
System.Collections.Generic;
using
System.Text;
namespace
Composite
...
{
/**//// <summary>
/// 透明模式 /// 一个Leaf类和一个Composite共享一个在抽象类中定义的公共接口
/// </summary> public interface ITransparence ...{ /**//// <summary> /// 获得学生的总成绩 /// </summary> /// <returns>返回学生的总成绩</returns> int GetStudentScores(); /**//// <summary> /// 获得学生的所有科目名称 /// </summary> /// <returns>返回学生的所有科目名称</returns> string GetStudentSubjects(); /**//// <summary> /// 增加叶节点 /// </summary> /// <param name="transparence">接口类型对象</param> /// <returns>操作是否成功</returns> bool Add(ITransparence transparence); /**//// <summary> /// 移除叶节点 /// </summary> /// <param name="transparence">接口类型对象</param> /// <returns>操作是否成功</returns> bool Remove(ITransparence transparence); /**//// <summary> /// 获得所有的子节点 /// </summary> /// <returns></returns> List<ITransparence> GetChild(); } /**//// <summary> /// 学生叶子节点 /// </summary> public class StudentLeaf : ITransparence ...{ /**//// <summary> /// 语文 /// </summary> private string _chinese; /**//// <summary> /// 数学 /// </summary> private string _math; /**//// <summary> /// 英语 /// </summary> private string _english; /**//// <summary> /// 语文成绩 /// </summary> private int _chineseScore; /**//// <summary> /// 数学成绩 /// </summary> private int _mathScore; /**//// <summary> /// 英语成绩 /// </summary> private int _englishScore; /**//// <summary> /// 构造函数：语文,数学,英语的中文名称和它的分数 /// </summary> /// <param name="chinese"></param> /// <param name="math"></param> /// <param name="english"></param> public StudentLeaf(string chinese, string math, string english, int chineseScore, int mathScore, int englishScore) ...{ _chinese = chinese; _math = math; _english = english; _chineseScore = chineseScore; _mathScore = mathScore; _englishScore = englishScore; } /**//// <summary> /// 获得某个学生总成绩 /// </summary> /// <returns></returns> public int GetStudentScores() ...{ int scores = _chineseScore + _mathScore + _englishScore; return scores; } /**//// <summary> /// 获得某个学生的所有科目名称 /// </summary> /// <returns></returns> public string GetStudentSubjects() ...{ StringBuilder sb = new StringBuilder(); sb.Append("语文:"); sb.Append(_chinese); sb.Append(" "); sb.Append("数学:"); sb.Append(_math); sb.Append(" "); sb.Append("英语:"); sb.Append(_english); sb.Append(" "); return sb.ToString(); } /**//// <summary> /// 增加叶节点 /// </summary> /// <param name="transparence">接口类型对象</param> /// <returns>操作是否成功</returns> public bool Add(ITransparence transparence) ...{ //叶子节点不能使用该方法 return false; } /**//// <summary> /// 移除叶节点 /// </summary> /// <param name="transparence">接口类型对象</param> /// <returns>操作是否成功</returns> public bool Remove(ITransparence transparence) ...{ //叶子节点不能使用该方法 return false; } /**//// <summary> /// 获得所有的子节点 /// </summary> /// <returns></returns> public List<ITransparence> GetChild() ...{ return null; } } /**//// <summary> /// 学生合成类 /// </summary> public class StudentComposite : ITransparence ...{ private List<ITransparence> studentComposite = new List<ITransparence>(); /**//// <summary> /// 获得某个学生总成绩 /// </summary> /// <returns></returns> public int GetStudentScores() ...{ int scores = 0; foreach(ITransparence transparence in studentComposite) ...{ scores += transparence.GetStudentScores(); } return scores; } /**//// <summary> /// 获得某个学生的所有科目名称 /// </summary> /// <returns></returns> public string GetStudentSubjects() ...{ StringBuilder sb = new StringBuilder(); foreach (ITransparence transparence in studentComposite) ...{ sb.Append(transparence.GetStudentSubjects()); sb.Append(" "); } return sb.ToString(); } /**//// <summary> /// 增加叶节点 /// </summary> /// <param name="transparence">接口类型对象</param> /// <returns>操作是否成功</returns> public bool Add(ITransparence transparence) ...{ studentComposite.Add(transparence); return true; } /**//// <summary> /// 移除叶节点 /// </summary> /// <param name="transparence">接口类型对象</param> /// <returns>操作是否成功</returns> public bool Remove(ITransparence transparence) ...{ studentComposite.Remove(transparence); return true; } /**//// <summary> /// 获得所有的子节点 /// </summary> /// <returns></returns> public List<ITransparence> GetChild() ...{ return studentComposite; } } /**//// <summary> /// 客户类 /// </summary> public class Client ...{ static void Main(string[] args) ...{ int scores = 0; string studentSubjectsName = string.Empty; StudentComposite sudentCompositeRoot = new StudentComposite(); StudentLeaf studentLeafRootOne = new StudentLeaf("11","12","13",70,71,72); StudentLeaf studentLeafRootTwo = new StudentLeaf("21","22","23",80,81,82); StudentLeaf studentLeafRootThree= new StudentLeaf("31","32","33",90,91,92); sudentCompositeRoot.Add(studentLeafRootOne); sudentCompositeRoot.Add(studentLeafRootTwo); sudentCompositeRoot.Add(studentLeafRootThree); StudentComposite sudentCompositeChild = new StudentComposite(); StudentLeaf studentLeafChildOne = new StudentLeaf("41","42","43",60,61,62); StudentLeaf studentLeafChildTwo = new StudentLeaf("51","52","53",50,51,52); sudentCompositeChild.Add(studentLeafChildOne); sudentCompositeChild.Add(studentLeafChildTwo); sudentCompositeRoot.Add(sudentCompositeChild); scores = sudentCompositeRoot.GetStudentScores(); Console.WriteLine(" 总成绩：{0} ", scores); studentSubjectsName = sudentCompositeRoot.GetStudentSubjects(); Console.WriteLine(" 所有科目名称：{0} ", studentSubjectsName); StudentLeaf studentLeaf = new StudentLeaf("61", "62", "63", 40, 41, 42); scores = studentLeaf.GetStudentScores(); Console.WriteLine(" 总成绩：{0} ", scores); studentSubjectsName = studentLeaf.GetStudentSubjects(); Console.WriteLine(" 所有科目名称：{0} ", studentSubjectsName); } }
}
安全模式：
公共接口Component中里面不声明所有的用来管理子类对象的方法，而将这些方法（Add()、Remove()，以及GetChild()方法）在Composite类中实现。因为叶对象不包含任何对象，所以叶对象不需要操作叶子对象的方法，故是安全的。在这种情况下，在客户端使用管理子类对象的方法，自然就出错了。
示例代码如下：
using
System;
using
System.Collections.Generic;
using
System.Text;
namespace
Composite
...
{ /**//// <summary> /// 安全模式 /// 一个Leaf类和一个Composite共享一个在抽象类中定义的公共接口 /// </summary> public interface ITransparence ...{ /**//// <summary> /// 获得学生的总成绩 /// </summary> /// <returns>返回学生的总成绩</returns> int GetStudentScores(); /**//// <summary> /// 获得学生的所有科目名称 /// </summary> /// <returns>返回学生的所有科目名称</returns> string GetStudentSubjects(); } /**//// <summary> /// 学生叶子节点 /// </summary> public class StudentLeaf : ITransparence ...{ /**//// <summary> /// 语文 /// </summary> private string _chinese; /**//// <summary> /// 数学 /// </summary> private string _math; /**//// <summary> /// 英语 /// </summary> private string _english; /**//// <summary> /// 语文成绩 /// </summary> private int _chineseScore; /**//// <summary> /// 数学成绩 /// </summary> private int _mathScore; /**//// <summary> /// 英语成绩 /// </summary> private int _englishScore; /**//// <summary> /// 构造函数：语文,数学,英语的中文名称和它的分数 /// </summary> /// <param name="chinese"></param> /// <param name="math"></param> /// <param name="english"></param> public StudentLeaf(string chinese, string math, string english, int chineseScore, int mathScore, int englishScore) ...{ _chinese = chinese; _math = math; _english = english; _chineseScore = chineseScore; _mathScore = mathScore; _englishScore = englishScore; } /**//// <summary> /// 获得某个学生总成绩 /// </summary> /// <returns></returns> public int GetStudentScores() ...{ int scores = _chineseScore + _mathScore + _englishScore; return scores; } /**//// <summary> /// 获得某个学生的所有科目名称 /// </summary> /// <returns></returns> public string GetStudentSubjects() ...{ StringBuilder sb = new StringBuilder(); sb.Append("语文:"); sb.Append(_chinese); sb.Append(" "); sb.Append("数学:"); sb.Append(_math); sb.Append(" "); sb.Append("英语:"); sb.Append(_english); sb.Append(" "); return sb.ToString(); } } /**//// <summary> /// 学生合成类 /// </summary> public class StudentComposite : ITransparence ...{ private List<ITransparence> studentComposite = new List<ITransparence>(); /**//// <summary> /// 获得某个学生总成绩 /// </summary> /// <returns></returns> public int GetStudentScores() ...{ int scores = 0; foreach(ITransparence transparence in studentComposite) ...{ scores += transparence.GetStudentScores(); } return scores; } /**//// <summary> /// 获得某个学生的所有科目名称 /// </summary> /// <returns></returns> public string GetStudentSubjects() ...{ StringBuilder sb = new StringBuilder(); foreach (ITransparence transparence in studentComposite) ...{ sb.Append(transparence.GetStudentSubjects()); sb.Append(" "); } return sb.ToString(); } /**//// <summary> /// 增加叶节点 /// </summary> /// <param name="transparence">接口类型对象</param> /// <returns>操作是否成功</returns> public bool Add(ITransparence transparence) ...{ studentComposite.Add(transparence); return true; } /**//// <summary> /// 移除叶节点 /// </summary> /// <param name="transparence">接口类型对象</param> /// <returns>操作是否成功</returns> public bool Remove(ITransparence transparence) ...{ studentComposite.Remove(transparence); return true; } /**//// <summary> /// 获得所有的子节点 /// </summary> /// <returns></returns> public List<ITransparence> GetChild() ...{ return studentComposite; } } /**//// <summary> /// 客户类 /// </summary> public class Client ...{ static void Main(string[] args) ...{ int scores = 0; string studentSubjectsName = string.Empty; StudentComposite sudentCompositeRoot = new StudentComposite(); StudentLeaf studentLeafRootOne = new StudentLeaf("11","12","13",70,71,72); StudentLeaf studentLeafRootTwo = new StudentLeaf("21","22","23",80,81,82); StudentLeaf studentLeafRootThree= new StudentLeaf("31","32","33",90,91,92); sudentCompositeRoot.Add(studentLeafRootOne); sudentCompositeRoot.Add(studentLeafRootTwo); sudentCompositeRoot.Add(studentLeafRootThree); StudentComposite sudentCompositeChild = new StudentComposite(); StudentLeaf studentLeafChildOne = new StudentLeaf("41","42","43",60,61,62); StudentLeaf studentLeafChildTwo = new StudentLeaf("51","52","53",50,51,52); sudentCompositeChild.Add(studentLeafChildOne); sudentCompositeChild.Add(studentLeafChildTwo); sudentCompositeRoot.Add(sudentCompositeChild); scores = sudentCompositeRoot.GetStudentScores(); Console.WriteLine(" 总成绩：{0} ", scores); studentSubjectsName = sudentCompositeRoot.GetStudentSubjects(); Console.WriteLine(" 所有科目名称：{0} ", studentSubjectsName); StudentLeaf studentLeaf = new StudentLeaf("61", "62", "63", 40, 41, 42); scores = studentLeaf.GetStudentScores(); Console.WriteLine(" 总成绩：{0} ", scores); studentSubjectsName = studentLeaf.GetStudentSubjects(); Console.WriteLine(" 所有科目名称：{0} ", studentSubjectsName); } }}
参考资料:
(1)《C# 设计模式》《 Desing Patterns in C#》(美)Steven John Metsker 著， 颜炯 译。
(2)设计模式 可复用面向对象软件的基础 Design Patterns Elements of Reusable Object-Oriented Software 》（美）Erich Gamma Richard Helm Ralph Johnson John Vlissides 著，李英军 等译。