行为型设计模式之迭代器模式

  1 using System;
  2     using System.Collections;
  3 
  4     class Node 
  5     {
  6         private string name;
  7         public string Name 
  8         {
  9             get 
 10             {
 11                 return name;    
 12             }
 13         }
 14         public Node(string s)
 15         {
 16             name = s;
 17         }
 18     }
 19     
 20     class NodeCollection 
 21     {
 22         private ArrayList list = new ArrayList();
 23         private int nodeMax = 0;
 24         
 25         // left as a student exercise - implement collection
 26         // functions to remove and edit entries also
 27         public void AddNode(Node n)
 28         {
 29             list.Add(n); 
 30             nodeMax++;            
 31         }        
 32         public Node GetNode(int i)
 33         {
 34             return ((Node) list[i]);
 35         }
 36 
 37         public int NodeMax 
 38         {            
 39             get 
 40             {
 41                 return nodeMax;
 42             }
 43         }
 44     }
 45 
 46     /*
 47      * The iterator needs to understand how to traverse the collection 
 48      * It can do that as way it pleases - forward, reverse, depth-first, 
 49      */
 50     abstract class Iterator 
 51     {
 52         abstract public Node Next();        
 53     }
 54 
 55     class ReverseIterator : Iterator
 56     {
 57         private NodeCollection nodeCollection;
 58         private int currentIndex;
 59 
 60         public ReverseIterator (NodeCollection c)
 61         {
 62             nodeCollection = c;            
 63             currentIndex = c.NodeMax -1; // array index starts at 0!
 64         }
 65 
 66         // note: as the code stands, if the collection changes,
 67         // the iterator needs to be restarted 
 68         override public Node Next()
 69         {
 70             if (currentIndex == -1)
 71                 return null;
 72             else 
 73                 return(nodeCollection.GetNode(currentIndex--));
 74         }
 75     }
 76     
 77     /// <summary>
 78     ///    Summary description for Client.
 79     /// </summary>
 80     public class Client
 81     {
 82         public static int Main(string[] args)
 83         {   
 84             NodeCollection c = new NodeCollection();
 85             c.AddNode(new Node("first"));
 86             c.AddNode(new Node("second"));
 87             c.AddNode(new Node("third"));
 88 
 89             // now use iterator to traverse this
 90             ReverseIterator i = new ReverseIterator(c);
 91 
 92             // the code below will work with any iterator type
 93             Node n;
 94             do 
 95             {
 96                 n = i.Next();
 97                 if (n != null) 
 98                     Console.WriteLine("{0}", n.Name);
 99             } while (n != null);
100                 
101             return 0;
102         }
103     }