组合模式

场景：

1.希望把对象表示成部分—整体层次结构；

2.希望用户忽略组合对象与单个对象的不同，用户将统一地使用组合结构中所有对象。

UML图：

示例代码：

    public 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);
    }

    public class Leaf:Component
    {
        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);
        }

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

    public class Composite:Component
    {
        private List<Component> _children = new List<Component>();
        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);
            }
        }

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

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

            // Add and remove a leaf
            Leaf leaf = new Leaf("Leaf D");
            root.Add(leaf);
            root.Remove(leaf);

            // Recursively display tree
            root.Display(1);
        }
    }