迭代器模式(Iterator Pattern)

清疚 2022-04-10 09:23 250阅读 0赞

[设计模式 - 吕震宇][-]

[.NET设计模式系列文章][.NET]

[薛敬明的专栏][Link 1]

[乐在其中设计模式(C\#)][C]

# [.NET设计模式（18）：迭代器模式（Iterator Pattern）][.NET_18_Iterator Pattern] #

**概述**

在面向对象的软件设计中，我们经常会遇到一类集合对象，这类集合对象的内部结构可能有着各种各样的实现，但是归结起来，无非有两点是需要我们去关心的：一是集合内部的数据存储结构，二是遍历集合内部的数据。面向对象设计原则中有一条是类的单一职责原则，所以我们要尽可能的去分解这些职责，用不同的类去承担不同的职责。Iterator模式就是分离了集合对象的遍历行为，抽象出一个迭代器类来负责，这样既可以做到不暴露集合的内部结构，又可让外部代码透明的访问集合内部的数据。

**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。\[GOF 《设计模式》\]

**结构图**

Iterator模式结构图如下：

![iterator_01.gif][]

图1 Iterator模式结构图

**生活中的例子**

迭代器提供一种方法顺序访问一个集合对象中各个元素，而又不需要暴露该对象的内部表示。在早期的电视机中，一个拨盘用来改变频道。当改变频道时，需要手工转动拨盘移过每一个频道，而不论这个频道是否有信号。现在的电视机，使用\[后一个\]和\[前一个\]按钮。当按下\[后一个\]按钮时，将切换到下一个预置的频道。想象一下在陌生的城市中的旅店中看电视。当改变频道时，重要的不是几频道，而是节目内容。如果对一个频道的节目不感兴趣，那么可以换下一个频道，而不需要知道它是几频道。

![iterator_02.gif][]

图2 使用选频器做例子的Iterator模式对象图

**Iterator模式解说**

![Iterator_03.jpg][]

图3 示例代码结构图

首先有一个抽象的聚集，所谓的聚集就是就是数据的集合，可以循环去访问它。它只有一个方法GetIterator()让子类去实现，用来获得一个迭代器对象。

![ExpandedBlockStart.gif][] ///<summary>  
![InBlock.gif][]  
![InBlock.gif][]/// 抽象聚集  
![InBlock.gif][]  
![ExpandedBlockEnd.gif][]///</summary>  
![None.gif][]   
![None.gif][] public  interface  IList  
![None.gif][]  
![ExpandedBlockStart.gif][] \{  
![InBlock.gif][] IIterator GetIterator();  
![ExpandedBlockEnd.gif][]\}

抽象的迭代器，它是用来访问聚集的类，封装了一些方法，用来把聚集中的数据按顺序读取出来。通常会有MoveNext()、CurrentItem()、Fisrt()、Next()等几个方法让子类去实现。

![ExpandedBlockStart.gif][] ///<summary>  
![InBlock.gif][]  
![InBlock.gif][]/// 抽象迭代器  
![InBlock.gif][]  
![ExpandedBlockEnd.gif][]///</summary>  
![None.gif][]   
![None.gif][] public  interface  IIterator  
![ExpandedBlockStart.gif][] \{  
![InBlock.gif][]bool MoveNext();  
![InBlock.gif][]  
![InBlock.gif][] Object CurrentItem();  
![InBlock.gif][]  
![InBlock.gif][]void First();  
![InBlock.gif][]  
![InBlock.gif][]void Next();  
![ExpandedBlockEnd.gif][]\}

具体的聚集，它实现了抽象聚集中的唯一的方法，同时在里面保存了一组数据，这里我们加上Length属性和GetElement()方法是为了便于访问聚集中的数据。

![ExpandedBlockStart.gif][] ///<summary>  
![InBlock.gif][]  
![InBlock.gif][]/// 具体聚集  
![InBlock.gif][]  
![ExpandedBlockEnd.gif][]///</summary>  
![None.gif][]   
![None.gif][] public  class  ConcreteList : IList  
![ExpandedBlockStart.gif][] \{  
![InBlock.gif][]int\[\] list;  
![InBlock.gif][]  
![InBlock.gif][]public ConcreteList()  
![InBlock.gif][]  
![ExpandedSubBlockStart.gif][]\{  
![ExpandedSubBlockStart.gif][] list =newint\[\] \{ 1,2,3,4,5\};  
![ExpandedSubBlockEnd.gif][] \}  
![InBlock.gif][]  
![InBlock.gif][]public IIterator GetIterator()  
![InBlock.gif][]  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][]returnnew ConcreteIterator(this);  
![ExpandedSubBlockEnd.gif][] \}  
![InBlock.gif][]  
![InBlock.gif][]publicint Length  
![InBlock.gif][]  
![ExpandedSubBlockStart.gif][]\{  
![ExpandedSubBlockStart.gif][]get\{ return list.Length; \}  
![ExpandedSubBlockEnd.gif][] \}  
![InBlock.gif][]  
![InBlock.gif][]publicint GetElement(int index)  
![InBlock.gif][]  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][]return list\[index\];  
![ExpandedSubBlockEnd.gif][] \}  
![ExpandedBlockEnd.gif][]\}

具体迭代器，实现了抽象迭代器中的四个方法，在它的构造函数中需要接受一个具体聚集类型的参数，在这里面我们可以根据实际的情况去编写不同的迭代方式。

![ExpandedBlockStart.gif][] ///<summary>  
![InBlock.gif][]  
![InBlock.gif][]/// 具体迭代器  
![InBlock.gif][]  
![ExpandedBlockEnd.gif][]///</summary>  
![None.gif][]   
![None.gif][] public  class  ConcreteIterator : IIterator  
![None.gif][]  
![ExpandedBlockStart.gif][] \{  
![InBlock.gif][]private ConcreteList list;  
![InBlock.gif][]  
![InBlock.gif][]privateint index;  
![InBlock.gif][]  
![InBlock.gif][]public ConcreteIterator(ConcreteList list)  
![InBlock.gif][]  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][]this.list = list;  
![InBlock.gif][]  
![InBlock.gif][] index =0;  
![ExpandedSubBlockEnd.gif][] \}  
![InBlock.gif][]  
![InBlock.gif][]publicbool MoveNext()  
![InBlock.gif][]  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][]if (index < list.Length)  
![InBlock.gif][]  
![InBlock.gif][]returntrue;  
![InBlock.gif][]  
![InBlock.gif][]else  
![InBlock.gif][]  
![InBlock.gif][]returnfalse;  
![ExpandedSubBlockEnd.gif][] \}  
![InBlock.gif][]  
![InBlock.gif][]public Object CurrentItem()  
![InBlock.gif][]  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][]return list.GetElement(index) ;  
![ExpandedSubBlockEnd.gif][] \}  
![InBlock.gif][]  
![InBlock.gif][]publicvoid First()  
![InBlock.gif][]  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][] index =0;  
![ExpandedSubBlockEnd.gif][] \}  
![InBlock.gif][]  
![InBlock.gif][]publicvoid Next()  
![InBlock.gif][]  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][]if (index < list.Length)  
![InBlock.gif][]  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][] index\++;  
![ExpandedSubBlockEnd.gif][] \}  
![ExpandedSubBlockEnd.gif][] \}  
![ExpandedBlockEnd.gif][]\}

简单的客户端程序调用：

![ExpandedBlockStart.gif][] ///<summary>  
![InBlock.gif][]  
![InBlock.gif][]/// 客户端程序  
![InBlock.gif][]  
![ExpandedBlockEnd.gif][]///</summary>  
![None.gif][]   
![None.gif][] class  Program  
![None.gif][]  
![ExpandedBlockStart.gif][] \{  
![InBlock.gif][]staticvoid Main(string\[\] args)  
![InBlock.gif][]  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][] IIterator iterator;  
![InBlock.gif][]  
![InBlock.gif][] IList list =new ConcreteList();  
![InBlock.gif][]  
![InBlock.gif][] iterator = list.GetIterator();  
![InBlock.gif][]  
![InBlock.gif][]while (iterator.MoveNext())  
![InBlock.gif][]  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][]int i = (int)iterator.CurrentItem();  
![InBlock.gif][] Console.WriteLine(i.ToString());  
![InBlock.gif][]  
![InBlock.gif][] iterator.Next();  
![ExpandedSubBlockEnd.gif][] \}  
![InBlock.gif][]  
![InBlock.gif][] Console.Read();  
![InBlock.gif][]  
![ExpandedSubBlockEnd.gif][] \}  
![InBlock.gif][]  
![ExpandedBlockEnd.gif][]\}

一个简单的迭代器示例就结束了，这里我们并没有利用任何的.NET特性，在C\#中，实现Iterator模式已经不需要这么麻烦了，已经C\#语言本身就有一些特定的实现，下面会说到。

**.NET中的Iterator模式**

在.NET下实现Iterator模式，对于聚集接口和迭代器接口已经存在了，其中IEnumerator扮演的就是迭代器的角色，它的实现如下：

![None.gif][] public  interface  IEumerator  
![None.gif][]  
![ExpandedBlockStart.gif][] \{  
![InBlock.gif][]object Current  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][]get;  
![ExpandedSubBlockEnd.gif][] \}  
![InBlock.gif][]  
![InBlock.gif][]bool MoveNext();  
![InBlock.gif][]  
![InBlock.gif][]void Reset();  
![InBlock.gif][]  
![ExpandedBlockEnd.gif][]\}

属性Current返回当前集合中的元素，Reset()方法恢复初始化指向的位置，MoveNext()方法返回值true表示迭代器成功前进到集合中的下一个元素，返回值false表示已经位于集合的末尾。能够提供元素遍历的集合对象，在.Net中都实现了IEnumerator接口。

IEnumerable则扮演的就是抽象聚集的角色，只有一个GetEnumerator()方法，如果集合对象需要具备跌代遍历的功能，就必须实现该接口。

![None.gif][] public  interface  IEnumerable  
![None.gif][]  
![ExpandedBlockStart.gif][] \{  
![InBlock.gif][] IEumerator GetEnumerator();  
![ExpandedBlockEnd.gif][]\}

下面看一个在.NET1.1下的迭代器例子，Person类是一个可枚举的类。PersonsEnumerator类是一个枚举器类。这个例子来自于[http://www.theserverside.net/][http_www.theserverside.net]，被我简单的改造了一下。

![None.gif][] public  class  Persons : IEnumerable  
![None.gif][]  
![ExpandedBlockStart.gif][] \{  
![InBlock.gif][]publicstring\[\] m\_Names;  
![InBlock.gif][]  
![InBlock.gif][]public Persons(paramsstring\[\] Names)  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][] m\_Names =newstring\[Names.Length\];  
![InBlock.gif][]  
![InBlock.gif][] Names.CopyTo(m\_Names,0);  
![ExpandedSubBlockEnd.gif][] \}  
![InBlock.gif][]  
![InBlock.gif][]privatestringthis\[int index\]  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][]get  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][]return m\_Names\[index\];  
![ExpandedSubBlockEnd.gif][] \}  
![InBlock.gif][]  
![InBlock.gif][]set  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][] m\_Names\[index\] = value;  
![ExpandedSubBlockEnd.gif][] \}  
![ExpandedSubBlockEnd.gif][] \}  
![InBlock.gif][]  
![InBlock.gif][]public IEnumerator GetEnumerator()  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][]returnnew PersonsEnumerator(this);  
![ExpandedSubBlockEnd.gif][] \}  
![ExpandedBlockEnd.gif][]\}   
![None.gif][]  
![None.gif][]  
![None.gif][] public  class  PersonsEnumerator : IEnumerator  
![ExpandedBlockStart.gif][] \{  
![InBlock.gif][]privateint index =\-1;  
![InBlock.gif][]  
![InBlock.gif][]private Persons P;  
![InBlock.gif][]  
![InBlock.gif][]public PersonsEnumerator(Persons P)  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][]this.P = P;  
![ExpandedSubBlockEnd.gif][] \}  
![InBlock.gif][]  
![InBlock.gif][]publicbool MoveNext()  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][] index\++;  
![InBlock.gif][]  
![InBlock.gif][]return index < P.m\_Names.Length;  
![ExpandedSubBlockEnd.gif][] \}  
![InBlock.gif][]  
![InBlock.gif][]publicvoid Reset()  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][] index =\-1;  
![ExpandedSubBlockEnd.gif][] \}  
![InBlock.gif][]  
![InBlock.gif][]publicobject Current  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][]get  
![InBlock.gif][]  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][]return P.m\_Names\[index\];  
![ExpandedSubBlockEnd.gif][] \}  
![ExpandedSubBlockEnd.gif][] \}  
![ExpandedBlockEnd.gif][]\}

来看客户端代码的调用：

![None.gif][] class  Program  
![ExpandedBlockStart.gif][] \{  
![InBlock.gif][]staticvoid Main(string\[\] args)  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][] Persons arrPersons =new Persons("Michel","Christine","Mathieu","Julien");  
![InBlock.gif][]  
![InBlock.gif][]foreach (string s in arrPersons)  
![InBlock.gif][]  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][] Console.WriteLine(s);  
![ExpandedSubBlockEnd.gif][] \}  
![InBlock.gif][]  
![InBlock.gif][] Console.ReadLine();  
![ExpandedSubBlockEnd.gif][] \}  
![ExpandedBlockEnd.gif][]\}

程序将输出：

![None.gif][] Michel  
![None.gif][]  
![None.gif][]Christine  
![None.gif][]  
![None.gif][]Mathieu  
![None.gif][]  
![None.gif][]Julien

现在我们分析编译器在执行foreach语句时到底做了什么，它执行的代码大致如下：

![None.gif][] class  Program  
![None.gif][]  
![ExpandedBlockStart.gif][] \{  
![InBlock.gif][]staticvoid Main(string\[\] args)  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][] Persons arrPersons =new Persons("Michel","Christine","Mathieu","Julien");  
![InBlock.gif][]  
![InBlock.gif][] IEnumerator e = arrPersons.GetEnumerator();  
![InBlock.gif][]  
![InBlock.gif][]while (e.MoveNext())  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][] Console.WriteLine((string)e.Current);  
![InBlock.gif][]  
![ExpandedSubBlockEnd.gif][] \}  
![InBlock.gif][]  
![InBlock.gif][] Console.ReadLine();  
![ExpandedSubBlockEnd.gif][] \}  
![ExpandedBlockEnd.gif][]\}

可以看到这段代码跟我们最前面提到的示例代码非常的相似。同时在这个例子中，我们把大部分的精力都花在了实现迭代器和可迭代的类上面，在.NET2.0下面，由于有了yield return关键字，实现起来将更加的简单优雅。下面我们把刚才的例子在2.0下重新实现一遍：

![None.gif][] public  class  Persons : IEnumerable  
![ExpandedBlockStart.gif][] \{  
![InBlock.gif][]string\[\] m\_Names;  
![InBlock.gif][]  
![InBlock.gif][]public Persons(paramsstring\[\] Names)  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][] m\_Names =newstring\[Names.Length\];  
![InBlock.gif][]  
![InBlock.gif][] Names.CopyTo(m\_Names,0);  
![ExpandedSubBlockEnd.gif][] \}  
![InBlock.gif][]  
![InBlock.gif][]public IEnumerator GetEnumerator()  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][]foreach (string s in m\_Names)  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][] yield return s;  
![ExpandedSubBlockEnd.gif][] \}  
![ExpandedSubBlockEnd.gif][] \}  
![ExpandedBlockEnd.gif][]\}   
![None.gif][]  
![None.gif][] class  Program  
![ExpandedBlockStart.gif][] \{  
![InBlock.gif][]staticvoid Main(string\[\] args)  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][] Persons arrPersons =new Persons("Michel","Christine","Mathieu","Julien");  
![InBlock.gif][]  
![InBlock.gif][]foreach (string s in arrPersons)  
![ExpandedSubBlockStart.gif][]\{  
![InBlock.gif][] Console.WriteLine(s);  
![ExpandedSubBlockEnd.gif][] \}  
![InBlock.gif][]  
![InBlock.gif][] Console.ReadLine();  
![ExpandedSubBlockEnd.gif][] \}  
![ExpandedBlockEnd.gif][]\}

程序将输出：

![None.gif][] Michel  
![None.gif][]  
![None.gif][]Christine  
![None.gif][]  
![None.gif][]Mathieu  
![None.gif][]  
![None.gif][]Julien

实现相同的功能，由于有了yield return关键字，变得非常的简单。好了，关于.NET中的Iterator模式就说这么多了，更详细的内容大家可以参考相关的资料。

**效果及实现要点**

1．迭代抽象：访问一个聚合对象的内容而无需暴露它的内部表示。

2．迭代多态：为遍历不同的集合结构提供一个统一的接口，从而支持同样的算法在不同的集合结构上进行操作。

3．迭代器的健壮性考虑：遍历的同时更改迭代器所在的集合结构，会导致问题。

**适用性**

1．访问一个聚合对象的内容而无需暴露它的内部表示。

2．支持对聚合对象的多种遍历。

3．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)。

**总结**

Iterator模式就是分离了集合对象的遍历行为，抽象出一个迭代器类来负责，这样既可以做到不暴露集合的内部结构，又可让外部代码透明的访问集合内部的数据。

**参考资料**

Erich Gamma等，《设计模式：可复用面向对象软件的基础》，机械工业出版社

Robert C.Martin，《敏捷软件开发：原则、模式与实践》，清华大学出版社

阎宏，《Java与模式》，电子工业出版社

Alan Shalloway James R. Trott，《Design Patterns Explained》，中国电力出版社

MSDN WebCast 《C\#面向对象设计模式纵横谈(18)：Iterator 迭代器模式(行为型模式)》

# [设计模式21：Iterator Pattern (迭代器模式)][21_Iterator Pattern] #

可以查看英文原文：[http://www.dofactory.com/Patterns/PatternIterator.aspx][http_www.dofactory.com_Patterns_PatternIterator.aspx]

### 一、迭代器模式：Iterator Pattern ###

Define：Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation.

定义：提供一种方式可以连续的访问几何对象的所有元素而无须关注内在的描述方式。

### 二、UML图 ###

![iterator][]

*  **Iterator** **(AbstractIterator)**
    
     *  定义一个访问和操作元素的接口
 *  **ConcreteIterator** **(Iterator)**
    
     *  实现迭代器的接口
     *  keeps track of the current position in the traversal of the aggregate.
 *  **Aggregate** **(AbstractCollection)**
    
     *  定义一个接口用于创建一个迭代器对象
 *  **ConcreteAggregate** **(Collection)**
    
     *  实现迭代器创建的接口并且返回一个合适的ConcreteIterator实例对象
    
    ### 三、迭代器模式实例代码 ###
    
    **\[c-sharp\]** [ view plain][view plain] [copy][view plain]
    
    1.  using System;
    2.  using System.Collections;
    3.  using System.Collections.Generic;
    4.  using System.Linq;
    5.  using System.Text;
    6.  
    7.  namespace Iterator\_Pattern
    8.  \{
    9.  /// <summary>
    10. 
    11. /// MainApp startup class for Structural 
    12. 
    13. /// Iterator Design Pattern.
    14. 
    15. /// </summary>
    16. 
    17. class MainApp
    18. \{
    19. 
    20. /// <summary>
    21. 
    22. /// Entry point into console application.
    23. 
    24. /// </summary>
    25. 
    26. static void Main()
    27. \{
    28. 
    29. ConcreteAggregate a = new ConcreteAggregate();
    30. 
    31. a\[0\] = "Item A";
    32. 
    33. a\[1\] = "Item B";
    34. 
    35. a\[2\] = "Item C";
    36. 
    37. a\[3\] = "Item D";
    38. 
    39. 
    40. 
    41. // Create Iterator and provide aggregate
    42. 
    43. ConcreteIterator i = new ConcreteIterator(a);
    44. 
    45. 
    46. 
    47. Console.WriteLine("Iterating over collection:");
    48. 
    49. 
    50. 
    51. object item = i.First();
    52. 
    53. while (item != null)
    54. \{
    55. 
    56. Console.WriteLine(item);
    57. 
    58. item = i.Next();
    59. 
    60. \}
    61. 
    62. 
    63. 
    64. // Wait for user
    65. 
    66. Console.ReadKey();
    67. 
    68. \}
    69. 
    70. \}
    71. 
    72. 
    73. 
    74. /// <summary>
    75. 
    76. /// The 'Aggregate' abstract class
    77. 
    78. /// </summary>
    79. 
    80. abstract class Aggregate
    81. \{
    82. 
    83. public abstract Iterator CreateIterator();
    84. 
    85. \}
    86. 
    87. 
    88. 
    89. /// <summary>
    90. 
    91. /// The 'ConcreteAggregate' class
    92. 
    93. /// </summary>
    94. 
    95. class ConcreteAggregate : Aggregate
    96. \{
    97. 
    98. private ArrayList \_items = new ArrayList();
    99. 
    100. 
    101. 
    102. public override Iterator CreateIterator()
    103. \{
    104. 
    105. return new ConcreteIterator(this);
    106. 
    107. \}
    108. 
    109. 
    110. 
    111. // Gets item count
    112. 
    113. public int Count
    114. \{
    115. 
    116. get \{ return \_items.Count; \}
    117. 
    118. \}
    119. 
    120. 
    121. 
    122. // Indexer
    123. 
    124. public object this\[int index\]
    125. \{
    126. 
    127. get \{ return \_items\[index\]; \}
    128. 
    129. set \{ \_items.Insert(index, value); \}
    130. 
    131. \}
    132. 
    133. \}
    134. 
    135. 
    136. 
    137. /// <summary>
    138. 
    139. /// The 'Iterator' abstract class
    140. 
    141. /// </summary>
    142. 
    143. abstract class Iterator
    144. \{
    145. 
    146. public abstract object First();
    147. 
    148. public abstract object Next();
    149. 
    150. public abstract bool IsDone();
    151. 
    152. public abstract object CurrentItem();
    153. 
    154. \}
    155. 
    156. 
    157. 
    158. /// <summary>
    159. 
    160. /// The 'ConcreteIterator' class
    161. 
    162. /// </summary>
    163. 
    164. class ConcreteIterator : Iterator
    165. \{
    166. 
    167. private ConcreteAggregate \_aggregate;
    168. 
    169. private int \_current = 0;
    170. 
    171. 
    172. 
    173. // Constructor
    174. 
    175. public ConcreteIterator(ConcreteAggregate aggregate)
    176. \{
    177. 
    178. this.\_aggregate = aggregate;
    179. 
    180. \}
    181. 
    182. 
    183. 
    184. // Gets first iteration item
    185. 
    186. public override object First()
    187. \{
    188. 
    189. return \_aggregate\[0\];
    190. 
    191. \}
    192. 
    193. 
    194. 
    195. // Gets next iteration item
    196. 
    197. public override object Next()
    198. \{
    199. 
    200. object ret = null;
    201. 
    202. if (\_current < \_aggregate.Count - 1)
    203. \{
    204. 
    205. ret = \_aggregate\[++\_current\];
    206. 
    207. \}
    208. 
    209. 
    210. 
    211. return ret;
    212. 
    213. \}
    214. 
    215. 
    216. 
    217. // Gets current iteration item
    218. 
    219. public override object CurrentItem()
    220. \{
    221. 
    222. return \_aggregate\[\_current\];
    223. 
    224. \}
    225. 
    226. 
    227. 
    228. // Gets whether iterations are complete
    229. 
    230. public override bool IsDone()
    231. \{
    232. 
    233. return \_current >= \_aggregate.Count;
    234. 
    235. \}
    236. 
    237. \}
    238. \}
    
    ### 四、一个使用迭代器模式的例子 ###
    
    该例子借助迭代器模式实现以下操作：迭代访问items的元素并且跳过每个迭代过程中items中指定的数字。
    
    **\[c-sharp\]** [ view plain][view plain] [copy][view plain]
    
    1.  using System;
    2.  using System.Collections;
    3.  using System.Collections.Generic;
    4.  using System.Linq;
    5.  using System.Text;
    6.  
    7.  namespace Iterator\_Pattern
    8.  \{
    9.  /// <summary>
    10. 
    11. /// MainApp startup class for Real-World 
    12. 
    13. /// Iterator Design Pattern.
    14. 
    15. /// </summary>
    16. 
    17. class MainApp
    18. \{
    19. 
    20. /// <summary>
    21. 
    22. /// Entry point into console application.
    23. 
    24. /// </summary>
    25. 
    26. static void Main()
    27. \{
    28. 
    29. // Build a collection
    30. 
    31. Collection collection = new Collection();
    32. 
    33. collection\[0\] = new Item("Item 0");
    34. 
    35. collection\[1\] = new Item("Item 1");
    36. 
    37. collection\[2\] = new Item("Item 2");
    38. 
    39. collection\[3\] = new Item("Item 3");
    40. 
    41. collection\[4\] = new Item("Item 4");
    42. 
    43. collection\[5\] = new Item("Item 5");
    44. 
    45. collection\[6\] = new Item("Item 6");
    46. 
    47. collection\[7\] = new Item("Item 7");
    48. 
    49. collection\[8\] = new Item("Item 8");
    50. 
    51. 
    52. 
    53. // Create iterator
    54. 
    55. Iterator iterator = new Iterator(collection);
    56. 
    57. 
    58. 
    59. // Skip every other item
    60. 
    61. iterator.Step = 2;
    62. 
    63. 
    64. 
    65. Console.WriteLine("Iterating over collection:");
    66. 
    67. 
    68. 
    69. for (Item item = iterator.First();
    70. 
    71. !iterator.IsDone; item = iterator.Next())
    72. \{
    73. 
    74. Console.WriteLine(item.Name);
    75. 
    76. \}
    77. 
    78. 
    79. 
    80. // Wait for user
    81. 
    82. Console.ReadKey();
    83. 
    84. \}
    85. 
    86. \}
    87. 
    88. 
    89. 
    90. /// <summary>
    91. 
    92. /// A collection item
    93. 
    94. /// </summary>
    95. 
    96. class Item
    97. \{
    98. 
    99. private string \_name;
    100. 
    101. 
    102. 
    103. // Constructor
    104. 
    105. public Item(string name)
    106. \{
    107. 
    108. this.\_name = name;
    109. 
    110. \}
    111. 
    112. 
    113. 
    114. // Gets name
    115. 
    116. public string Name
    117. \{
    118. 
    119. get \{ return \_name; \}
    120. 
    121. \}
    122. 
    123. \}
    124. 
    125. 
    126. 
    127. /// <summary>
    128. 
    129. /// The 'Aggregate' interface
    130. 
    131. /// </summary>
    132. 
    133. interface IAbstractCollection
    134. \{
    135. 
    136. Iterator CreateIterator();
    137. 
    138. \}
    139. 
    140. 
    141. 
    142. /// <summary>
    143. 
    144. /// The 'ConcreteAggregate' class
    145. 
    146. /// </summary>
    147. 
    148. class Collection : IAbstractCollection
    149. \{
    150. 
    151. private ArrayList \_items = new ArrayList();
    152. 
    153. 
    154. 
    155. public Iterator CreateIterator()
    156. \{
    157. 
    158. return new Iterator(this);
    159. 
    160. \}
    161. 
    162. 
    163. 
    164. // Gets item count
    165. 
    166. public int Count
    167. \{
    168. 
    169. get \{ return \_items.Count; \}
    170. 
    171. \}
    172. 
    173. 
    174. 
    175. // Indexer
    176. 
    177. public object this\[int index\]
    178. \{
    179. 
    180. get \{ return \_items\[index\]; \}
    181. 
    182. set \{ \_items.Add(value); \}
    183. 
    184. \}
    185. 
    186. \}
    187. 
    188. 
    189. 
    190. /// <summary>
    191. 
    192. /// The 'Iterator' interface
    193. 
    194. /// </summary>
    195. 
    196. interface IAbstractIterator
    197. \{
    198. 
    199. Item First();
    200. 
    201. Item Next();
    202. 
    203. bool IsDone \{ get; \}
    204. 
    205. Item CurrentItem \{ get; \}
    206. 
    207. \}
    208. 
    209. 
    210. 
    211. /// <summary>
    212. 
    213. /// The 'ConcreteIterator' class
    214. 
    215. /// </summary>
    216. 
    217. class Iterator : IAbstractIterator
    218. \{
    219. 
    220. private Collection \_collection;
    221. 
    222. private int \_current = 0;
    223. 
    224. private int \_step = 1;
    225. 
    226. 
    227. 
    228. // Constructor
    229. 
    230. public Iterator(Collection collection)
    231. \{
    232. 
    233. this.\_collection = collection;
    234. 
    235. \}
    236. 
    237. 
    238. 
    239. // Gets first item
    240. 
    241. public Item First()
    242. \{
    243. 
    244. \_current = 0;
    245. 
    246. return \_collection\[\_current\] as Item;
    247. 
    248. \}
    249. 
    250. 
    251. 
    252. // Gets next item
    253. 
    254. public Item Next()
    255. \{
    256. 
    257. \_current += \_step;
    258. 
    259. if (!IsDone)
    260. 
    261. return \_collection\[\_current\] as Item;
    262. 
    263. else
    264. 
    265. return null;
    266. 
    267. \}
    268. 
    269. 
    270. 
    271. // Gets or sets stepsize
    272. 
    273. public int Step
    274. \{
    275. 
    276. get \{ return \_step; \}
    277. 
    278. set \{ \_step = value; \}
    279. 
    280. \}
    281. 
    282. 
    283. 
    284. // Gets current iterator item
    285. 
    286. public Item CurrentItem
    287. \{
    288. 
    289. get \{ return \_collection\[\_current\] as Item; \}
    290. 
    291. \}
    292. 
    293. 
    294. 
    295. // Gets whether iteration is complete
    296. 
    297. public bool IsDone
    298. \{
    299. 
    300. get \{ return \_current >= \_collection.Count; \}
    301. 
    302. \}
    303. 
    304. \}
    305. \}
    
    ## [乐在其中设计模式(C\#) - 迭代器模式(Iterator Pattern)][C_ - _Iterator Pattern] ##
    
    乐在其中设计模式(C\#) - 迭代器模式(Iterator Pattern)
    
      
      
    作者：[webabcd][]  
      
      
    介绍  
    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。  
      
      
    示例  
    有一个Message实体类，某聚合对象内的各个元素均为该实体对象，现在要提供一种方法顺序地访问这个聚合对象中的各个元素。  
    ![o_Iterator.png][]  
      
      
    MessageModel  
    
    
    ![None.gif][] using  System;  
    ![None.gif][] using  System.Collections.Generic;  
    ![None.gif][] using  System.Text;  
    ![None.gif][]  
    ![None.gif][] namespace  Pattern.Iterator  
    ![ExpandedBlockStart.gif][] \{  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// Message实体类  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]publicclass MessageModel  
    ![ExpandedSubBlockStart.gif][]\{  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 构造函数  
    ![InBlock.gif][]///</summary>  
    ![InBlock.gif][]///<param name="msg">Message内容</param>  
    ![ExpandedSubBlockEnd.gif][]///<param name="pt">Message发布时间</param>  
    ![InBlock.gif][]public MessageModel(string msg, DateTime pt)  
    ![ExpandedSubBlockStart.gif][]\{  
    ![InBlock.gif][]this.\_message = msg;  
    ![InBlock.gif][]this.\_publishTime = pt;  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![InBlock.gif][]  
    ![InBlock.gif][]privatestring \_message;  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// Message内容  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]publicstring Message  
    ![ExpandedSubBlockStart.gif][]\{  
    ![ExpandedSubBlockStart.gif][]get\{ return \_message; \}  
    ![ExpandedSubBlockStart.gif][]set\{ \_message = value; \}  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![InBlock.gif][]  
    ![InBlock.gif][]private DateTime \_publishTime;  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// Message发布时间  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]public DateTime PublishTime  
    ![ExpandedSubBlockStart.gif][]\{  
    ![ExpandedSubBlockStart.gif][]get\{ return \_publishTime; \}  
    ![ExpandedSubBlockStart.gif][]set\{ \_publishTime = value; \}  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![ExpandedBlockEnd.gif][]\}   
    ![None.gif][]
    
      
    ICollection  
    
    
    ![None.gif][] using  System;  
    ![None.gif][] using  System.Collections.Generic;  
    ![None.gif][] using  System.Text;  
    ![None.gif][]  
    ![None.gif][] namespace  Pattern.Iterator  
    ![ExpandedBlockStart.gif][] \{  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 集合接口（Aggregate）  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]publicinterface ICollection  
    ![ExpandedSubBlockStart.gif][]\{  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 创建迭代器对象  
    ![InBlock.gif][]///</summary>  
    ![ExpandedSubBlockEnd.gif][]///<returns></returns>  
    ![InBlock.gif][] IIterator CreateIterator();  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![ExpandedBlockEnd.gif][]\}   
    ![None.gif][]
    
      
    Collection  
    
    
    ![None.gif][] using  System;  
    ![None.gif][] using  System.Collections.Generic;  
    ![None.gif][] using  System.Text;  
    ![None.gif][]  
    ![None.gif][] namespace  Pattern.Iterator  
    ![ExpandedBlockStart.gif][] \{  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 集合（ConcreteAggregate）  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]publicclass Collection : ICollection  
    ![ExpandedSubBlockStart.gif][]\{  
    ![InBlock.gif][]private List<MessageModel> list =new List<MessageModel>();  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 创建迭代器对象  
    ![InBlock.gif][]///</summary>  
    ![ExpandedSubBlockEnd.gif][]///<returns></returns>  
    ![InBlock.gif][]public IIterator CreateIterator()  
    ![ExpandedSubBlockStart.gif][]\{  
    ![InBlock.gif][]returnnew Iterator(this);  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 集合内的对象总数  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]publicint Count  
    ![ExpandedSubBlockStart.gif][]\{  
    ![ExpandedSubBlockStart.gif][]get\{ return list.Count; \}  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 索引器  
    ![InBlock.gif][]///</summary>  
    ![InBlock.gif][]///<param name="index">index</param>  
    ![ExpandedSubBlockEnd.gif][]///<returns></returns>  
    ![InBlock.gif][]public MessageModel this\[int index\]  
    ![ExpandedSubBlockStart.gif][]\{  
    ![ExpandedSubBlockStart.gif][]get\{ return list\[index\]; \}  
    ![ExpandedSubBlockStart.gif][]set\{ list.Add(value); \}  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![InBlock.gif][]  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![ExpandedBlockEnd.gif][]\}   
    ![None.gif][]
    
      
    IIterator  
    
    
    ![None.gif][] using  System;  
    ![None.gif][] using  System.Collections.Generic;  
    ![None.gif][] using  System.Text;  
    ![None.gif][]  
    ![None.gif][] namespace  Pattern.Iterator  
    ![ExpandedBlockStart.gif][] \{  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 迭代器接口（IIterator）  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]publicinterface IIterator  
    ![ExpandedSubBlockStart.gif][]\{  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 第一个对象  
    ![InBlock.gif][]///</summary>  
    ![ExpandedSubBlockEnd.gif][]///<returns></returns>  
    ![InBlock.gif][] MessageModel First();  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 下一个对象  
    ![InBlock.gif][]///</summary>  
    ![ExpandedSubBlockEnd.gif][]///<returns></returns>  
    ![InBlock.gif][] MessageModel Next();  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 当前对象  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![ExpandedSubBlockStart.gif][] MessageModel CurrentMessageModel \{ get; \}  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 是否迭代完毕  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![ExpandedSubBlockStart.gif][]bool IsDone \{ get; \}  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![ExpandedBlockEnd.gif][]\}   
    ![None.gif][]
    
      
    Iterator  
    
    
    ![None.gif][] using  System;  
    ![None.gif][] using  System.Collections.Generic;  
    ![None.gif][] using  System.Text;  
    ![None.gif][]  
    ![None.gif][] namespace  Pattern.Iterator  
    ![ExpandedBlockStart.gif][] \{  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 迭代器（Iterator）  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]publicclass Iterator : IIterator  
    ![ExpandedSubBlockStart.gif][]\{  
    ![InBlock.gif][]private Collection \_collection;  
    ![InBlock.gif][]privateint \_current =0;  
    ![InBlock.gif][]privateint \_step =1;  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 构造函数  
    ![InBlock.gif][]///</summary>  
    ![ExpandedSubBlockEnd.gif][]///<param name="collection"></param>  
    ![InBlock.gif][]public Iterator(Collection collection)  
    ![ExpandedSubBlockStart.gif][]\{  
    ![InBlock.gif][]this.\_collection = collection;  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 第一个对象  
    ![InBlock.gif][]///</summary>  
    ![ExpandedSubBlockEnd.gif][]///<returns></returns>  
    ![InBlock.gif][]public MessageModel First()  
    ![ExpandedSubBlockStart.gif][]\{  
    ![InBlock.gif][] \_current =0;  
    ![InBlock.gif][]return \_collection\[\_current\];  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 下一个对象  
    ![InBlock.gif][]///</summary>  
    ![ExpandedSubBlockEnd.gif][]///<returns></returns>  
    ![InBlock.gif][]public MessageModel Next()  
    ![ExpandedSubBlockStart.gif][]\{  
    ![InBlock.gif][] \_current \+= \_step;  
    ![InBlock.gif][]  
    ![InBlock.gif][]if (!IsDone)  
    ![ExpandedSubBlockStart.gif][]\{  
    ![InBlock.gif][]return \_collection\[\_current\];  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![InBlock.gif][]else  
    ![ExpandedSubBlockStart.gif][]\{  
    ![InBlock.gif][]returnnull;  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 当前对象  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]public MessageModel CurrentMessageModel  
    ![ExpandedSubBlockStart.gif][]\{  
    ![ExpandedSubBlockStart.gif][]get\{ return \_collection\[\_current\]; \}  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 是否迭代完毕  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]publicbool IsDone  
    ![ExpandedSubBlockStart.gif][]\{  
    ![ExpandedSubBlockStart.gif][]get\{ return \_current >= \_collection.Count ?true : false; \}  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![InBlock.gif][]  
    ![ExpandedSubBlockStart.gif][]///<summary>  
    ![InBlock.gif][]/// 步长  
    ![ExpandedSubBlockEnd.gif][]///</summary>  
    ![InBlock.gif][]publicint Step  
    ![ExpandedSubBlockStart.gif][]\{  
    ![ExpandedSubBlockStart.gif][]get\{ return \_step; \}  
    ![ExpandedSubBlockStart.gif][]set\{ \_step = value; \}  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![ExpandedBlockEnd.gif][]\}   
    ![None.gif][]
    
      
      
    Test  
    
    
    ![None.gif][] using  System;  
    ![None.gif][] using  System.Data;  
    ![None.gif][] using  System.Configuration;  
    ![None.gif][] using  System.Collections;  
    ![None.gif][] using  System.Web;  
    ![None.gif][] using  System.Web.Security;  
    ![None.gif][] using  System.Web.UI;  
    ![None.gif][] using  System.Web.UI.WebControls;  
    ![None.gif][] using  System.Web.UI.WebControls.WebParts;  
    ![None.gif][] using  System.Web.UI.HtmlControls;  
    ![None.gif][]  
    ![None.gif][] using  I  =  Pattern.Iterator;  
    ![None.gif][]  
    ![None.gif][] public  partial  class  Iterator : System.Web.UI.Page  
    ![ExpandedBlockStart.gif][] \{  
    ![InBlock.gif][]protectedvoid Page\_Load(object sender, EventArgs e)  
    ![ExpandedSubBlockStart.gif][]\{  
    ![InBlock.gif][] I::Collection collection =new I::Collection();  
    ![InBlock.gif][]  
    ![InBlock.gif][] collection\[0\] =new I::MessageModel("第1条信息", DateTime.Now);  
    ![InBlock.gif][] collection\[1\] =new I::MessageModel("第2条信息", DateTime.Now);  
    ![InBlock.gif][] collection\[2\] =new I::MessageModel("第3条信息", DateTime.Now);  
    ![InBlock.gif][] collection\[3\] =new I::MessageModel("第4条信息", DateTime.Now);  
    ![InBlock.gif][] collection\[4\] =new I::MessageModel("第5条信息", DateTime.Now);  
    ![InBlock.gif][] collection\[5\] =new I::MessageModel("第6条信息", DateTime.Now);  
    ![InBlock.gif][] collection\[6\] =new I::MessageModel("第7条信息", DateTime.Now);  
    ![InBlock.gif][] collection\[7\] =new I::MessageModel("第8条信息", DateTime.Now);  
    ![InBlock.gif][] collection\[8\] =new I::MessageModel("第9条信息", DateTime.Now);  
    ![InBlock.gif][]  
    ![InBlock.gif][] I::Iterator iterator =new I::Iterator(collection);  
    ![InBlock.gif][]  
    ![InBlock.gif][] iterator.Step =2;  
    ![InBlock.gif][]  
    ![InBlock.gif][]for (I::MessageModel mm = iterator.First(); !iterator.IsDone; mm = iterator.Next())  
    ![ExpandedSubBlockStart.gif][]\{  
    ![InBlock.gif][] Response.Write(mm.Message);  
    ![InBlock.gif][] Response.Write("<br />");  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![ExpandedSubBlockEnd.gif][] \}  
    ![ExpandedBlockEnd.gif][]\}   
    ![None.gif][]
    
      
    运行结果  
    第1条信息  
    第3条信息  
    第5条信息  
    第7条信息  
    第9条信息  
      
      
    参考  
    [http://www.dofactory.com/Patterns/PatternIterator.aspx][http_www.dofactory.com_Patterns_PatternIterator.aspx]  
      
      
    OK  
    [\[源码下载\]][Link 2]

[-]: http://www.cnblogs.com/zhenyulu/category/6930.html
[.NET]: http://www.cnblogs.com/Terrylee/archive/2006/07/17/334911.html
[Link 1]: http://blog.csdn.net/rocket5725/article/category/559017
[C]: http://www.cnblogs.com/webabcd/category/82668.html
[.NET_18_Iterator Pattern]: http://www.cnblogs.com/Terrylee/archive/2006/09/16/Iterator_Pattern.html
[iterator_01.gif]: /images/20220401/c458ef519696485dbb6a50ca8efee11e.png
[iterator_02.gif]: /images/20220401/44d6f853e63d45ddbaf7eca26b9c80fd.png
[Iterator_03.jpg]: /images/20220401/4b5e3889713e4b22985dd4c904e98efb.png
[ExpandedBlockStart.gif]: /images/20220401/5743d58a09df4565a1d72b45b334b1ee.png
[InBlock.gif]: /images/20220401/7316d59a94a4403f9351def8c9f688b9.png
[ExpandedBlockEnd.gif]: /images/20220401/79ae6029bf1745949ad2f12f5ad645e4.png
[None.gif]: /images/20220401/9c8781c5aa2f41c1af0726370e3e96da.png
[ExpandedSubBlockStart.gif]: /images/20220401/1a687bedb448418a8882b161f5bbd287.png
[ExpandedSubBlockEnd.gif]: /images/20220401/635b6d110f7c4656aa8640075d2f6902.png
[http_www.theserverside.net]: http://www.theserverside.net/
[21_Iterator Pattern]: http://blog.csdn.net/rocket5725/article/details/4333744
[http_www.dofactory.com_Patterns_PatternIterator.aspx]: http://www.dofactory.com/Patterns/PatternIterator.aspx
[iterator]: http://www.dofactory.com/Patterns/Diagrams/iterator.gif
[view plain]: http://blog.csdn.net/rocket5725/article/details/4333744#
[C_ - _Iterator Pattern]: http://www.cnblogs.com/webabcd/archive/2007/05/17/750715.html
[webabcd]: http://webabcd.cnblogs.com/
[o_Iterator.png]: /images/20220401/2b809f0bbb42439f93aa19a921ad4c5c.png
[Link 2]: http://files.cnblogs.com/webabcd/Pattern.rar