行为型设计模式之迭代器模式(Iterator)

结构
意图	提供一种方法顺序访问一个聚合对象中各个元素, 而又不需暴露该对象的内部表示。
适用性	访问一个聚合对象的内容而无需暴露它的内部表示。 支持对聚合对象的多种遍历。 为遍历不同的聚合结构提供一个统一的接口(即, 支持多态迭代)。

 using System;
     using System.Collections;

     class Node
     {
         private string name;
         public string Name
         {
             get
             {
                 return name;
             }
         }
         public Node(string s)
         {
             name = s;
         }
     }

     class NodeCollection
     {
         private ArrayList list = new ArrayList();
         private int nodeMax = ;

         // left as a student exercise - implement collection
         // functions to remove and edit entries also
         public void AddNode(Node n)
         {
             list.Add(n);
             nodeMax++;
         }
         public Node GetNode(int i)
         {
             return ((Node) list[i]);
         }

         public int NodeMax
         {
             get
             {
                 return nodeMax;
             }
         }
     }

     /*
      * The iterator needs to understand how to traverse the collection
      * It can do that as way it pleases - forward, reverse, depth-first,
      */
     abstract class Iterator
     {
         abstract public Node Next();
     }

     class ReverseIterator : Iterator
     {
         private NodeCollection nodeCollection;
         private int currentIndex;

         public ReverseIterator (NodeCollection c)
         {
             nodeCollection = c;
             currentIndex = c.NodeMax -; // array index starts at 0!
         }

         // note: as the code stands, if the collection changes,
         // the iterator needs to be restarted
         override public Node Next()
         {
             if (currentIndex == -)
                 return null;
             else
                 return(nodeCollection.GetNode(currentIndex--));
         }
     }

     /// <summary>
     ///    Summary description for Client.
     /// </summary>
     public class Client
     {
         public static int Main(string[] args)
         {
             NodeCollection c = new NodeCollection();
             c.AddNode(new Node("first"));
             c.AddNode(new Node("second"));
             c.AddNode(new Node("third"));

             // now use iterator to traverse this
             ReverseIterator i = new ReverseIterator(c);

             // the code below will work with any iterator type
             Node n;
             do
             {
                 n = i.Next();
                 if (n != null)
                     Console.WriteLine("{0}", n.Name);
             } while (n != null);

             return ;
         }
     }

迭代器模式