C# 设计模式系列教程-组合模式

  /// <summary>
  /// 一个抽象构件，声明一个接口用于访问和管理Component的子部件
  /// </summary>
  public abstract class Component
  {
    protected string name;

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

    /// <summary>
    /// 增加一个节点
    /// </summary>
    /// <param name="component"></param>
    public abstract void Add(Component component);

    /// <summary>
    /// 移除一个节点
    /// </summary>
    /// <param name="component"></param>
    public abstract void Remove(Component component);

    /// <summary>
    /// 显示层级结构
    /// </summary>
    public abstract void Display(int level);
  }

  /// <summary>
  /// 叶子节点
  /// </summary>
  public class Leaf : Component
  {
    public Leaf(string name)
      : base(name)
    { }

    /// <summary>
    /// 由于叶子节点没有子节点，所以Add和Remove方法对它来说没有意义，但它继承自Component，这样做可以消除叶节点和枝节点对象在抽象层次的区别，它们具备完全一致的接口。
    /// </summary>
    /// <param name="component"></param>
    public override void Add(Component component)
    {
      Console.WriteLine("Can not add a component to a leaf.");
    }

    /// <summary>
    /// 实现它没有意义，只是提供了一个一致的调用接口
    /// </summary>
    /// <param name="component"></param>
    public override void Remove(Component component)
    {
      Console.WriteLine("Can not remove a component to a leaf.");
    }

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

  /// <summary>
  /// 定义有枝节点的行为，用来存储部件，实现在Component接口中对子部件有关的操作
  /// </summary>
  public class Composite : Component
  {
    public Composite(string name)
      : base(name)
    { }

    /// <summary>
    /// 一个子对象集合，用来存储其下属的枝节点和叶节点
    /// </summary>
    private List<Component> children = new List<Component>();

    /// <summary>
    /// 增加子节点
    /// </summary>
    /// <param name="component"></param>
    public override void Add(Component component)
    {
      children.Add(component);
    }

    /// <summary>
    /// 移除子节点
    /// </summary>
    /// <param name="component"></param>
    public override void Remove(Component component)
    {
      children.Remove(component);
    }

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

      // 遍历其子节点并显示
      foreach (Component component in children)
      {
        component.Display(level+2);
      }
    }
  }

  class Program
  {
    static void Main(string[] args)
    {
      // 生成树根，并为其增加两个叶子节点
      Component root = new Composite("Root");
      root.Add(new Leaf("Leaf A in Root"));
      root.Add(new Leaf("Leaf B in Root"));

      // 为根增加两个枝节点
      Component branchX = new Composite("Branch X in Root");
      Component branchY = new Composite("Branch Y in Root");
      root.Add(branchX);
      root.Add(branchY);

      // 为BranchX增加页节点
      branchX.Add(new Leaf("Leaf A in Branch X"));

      // 为BranchX增加枝节点
      Component branchZ = new Composite("Branch Z in Branch X");
      branchX.Add(branchZ);

      // 为BranchY增加叶节点
      branchY.Add(new Leaf("Leaf in Branch Y"));

      // 为BranchZ增加叶节点
      branchZ.Add(new Leaf("Leaf in Branch Z"));

      // 显示树
      root.Display(1);

      Console.Read();
    }
  }