二十四种设计模式：迭代器模式(Iterator Pattern)

迭代器模式(Iterator Pattern)

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。



　　MessageModel

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.Iterator
{
/// <summary>
/// Message实体类
/// </summary>
public class MessageModel
{
/// <summary>
/// 构造函数
/// </summary>
/// <param name="msg">Message内容</param>
/// <param name="pt">Message发布时间</param>
public MessageModel(string msg, DateTime pt)
{
this._message = msg;
this._publishTime = pt;
}

private string _message;
/// <summary>
/// Message内容
/// </summary>
public string Message
{
get { return _message; }
set { _message = value; }
}

private DateTime _publishTime;
/// <summary>
/// Message发布时间
/// </summary>
public DateTime PublishTime
{
get { return _publishTime; }
set { _publishTime = value; }
}
}
}

　　ICollection

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.Iterator
{
/// <summary>
/// 集合接口（Aggregate）
/// </summary>
public interface ICollection
{
/// <summary>
/// 创建迭代器对象
/// </summary>
/// <returns></returns>
IIterator CreateIterator();
}
}

　　Collection

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.Iterator
{
/// <summary>
/// 集合（ConcreteAggregate）
/// </summary>
public class Collection : ICollection
{
private List<MessageModel> list = new List<MessageModel>();

/// <summary>
/// 创建迭代器对象
/// </summary>
/// <returns></returns>
public IIterator CreateIterator()
{
return new Iterator(this);
}

/// <summary>
/// 集合内的对象总数
/// </summary>
public int Count
{
get { return list.Count; }
}

/// <summary>
/// 索引器
/// </summary>
/// <param name="index">index</param>
/// <returns></returns>
public MessageModel this[int index]
{
get { return list[index]; }
set { list.Add(value); }
}

}
}

　　IIterator

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.Iterator
{
/// <summary>
/// 迭代器接口（IIterator）
/// </summary>
public interface IIterator
{
/// <summary>
/// 第一个对象
/// </summary>
/// <returns></returns>
MessageModel First();

/// <summary>
/// 下一个对象
/// </summary>
/// <returns></returns>
MessageModel Next();

/// <summary>
/// 当前对象
/// </summary>
MessageModel CurrentMessageModel { get; }

/// <summary>
/// 是否迭代完毕
/// </summary>
bool IsDone { get; }
}
}

　　Iterator

using System;
using System.Collections.Generic;
using System.Text;

namespace Pattern.Iterator
{
/// <summary>
/// 迭代器（Iterator）
/// </summary>
public class Iterator : IIterator
{
private Collection _collection;
private int _current = 0;
private int _step = 1;

/// <summary>
/// 构造函数
/// </summary>
/// <param name="collection"></param>
public Iterator(Collection collection)
{
this._collection = collection;
}

/// <summary>
/// 第一个对象
/// </summary>
/// <returns></returns>
public MessageModel First()
{
_current = 0;
return _collection[_current];
}

/// <summary>
/// 下一个对象
/// </summary>
/// <returns></returns>
public MessageModel Next()
{
_current += _step;

if (!IsDone)
{
return _collection[_current];
}
else
{
return null;
}
}

/// <summary>
/// 当前对象
/// </summary>
public MessageModel CurrentMessageModel
{
get { return _collection[_current]; }
}

/// <summary>
/// 是否迭代完毕
/// </summary>
public bool IsDone
{
get { return _current >= _collection.Count ? true : false; }
}

/// <summary>
/// 步长
/// </summary>
public int Step
{
get { return _step; }
set { _step = value; }
}
}
}

　　Test

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;

using I = Pattern.Iterator;

public partial class Iterator : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
I::Collection collection = new I::Collection();

collection[0] = new I::MessageModel("第1条信息", DateTime.Now);
collection[1] = new I::MessageModel("第2条信息", DateTime.Now);
collection[2] = new I::MessageModel("第3条信息", DateTime.Now);
collection[3] = new I::MessageModel("第4条信息", DateTime.Now);
collection[4] = new I::MessageModel("第5条信息", DateTime.Now);
collection[5] = new I::MessageModel("第6条信息", DateTime.Now);
collection[6] = new I::MessageModel("第7条信息", DateTime.Now);
collection[7] = new I::MessageModel("第8条信息", DateTime.Now);
collection[8] = new I::MessageModel("第9条信息", DateTime.Now);

I::Iterator iterator = new I::Iterator(collection);

iterator.Step = 2;

for (I::MessageModel mm = iterator.First(); !iterator.IsDone; mm = iterator.Next())
{
Response.Write(mm.Message);
Response.Write("<br />");
}
}
}

　　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