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{    /// 
    /// Message实体类    /// 
    public class MessageModel    {        /// 
        /// 构造函数        /// 
        /// Message内容        /// Message发布时间        public MessageModel(string msg, DateTime pt)        {            this._message = msg;            this._publishTime = pt;        }        private string _message;        /// 
        /// Message内容        /// 
        public string Message        {            get { return _message; }            set { _message = value; }        }        private DateTime _publishTime;        /// 
        /// Message发布时间        /// 
        public DateTime PublishTime        {            get { return _publishTime; }            set { _publishTime = value; }        }    }}

　　ICollection

using System;using System.Collections.Generic;using System.Text;namespace Pattern.Iterator{    /// 
    /// 集合接口（Aggregate）    /// 
    public interface ICollection    {        /// 
        /// 创建迭代器对象        /// 
        /// 
             IIterator CreateIterator();    }}

　　Collection

using System;using System.Collections.Generic;using System.Text;namespace Pattern.Iterator{    /// 
    /// 集合（ConcreteAggregate）    /// 
    public class Collection : ICollection    {        private List
     
       list = new List
      
       ();        /// 
       
        /// 创建迭代器对象        /// 
        /// 
               public IIterator CreateIterator()        {            return new Iterator(this);        }        /// 
       
        /// 集合内的对象总数        /// 
        public int Count        {            get { return list.Count; }        }        /// 
       
        /// 索引器        /// 
        /// 
       index        /// 
               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{    /// 
    /// 迭代器接口（IIterator）    /// 
    public interface IIterator    {        /// 
        /// 第一个对象        /// 
        /// 
             MessageModel First();        /// 
        /// 下一个对象        /// 
        /// 
             MessageModel Next();        /// 
        /// 当前对象        /// 
        MessageModel CurrentMessageModel { get; }        /// 
        /// 是否迭代完毕        /// 
        bool IsDone { get; }    }}

　　Iterator

using System;using System.Collections.Generic;using System.Text;namespace Pattern.Iterator{    /// 
    /// 迭代器（Iterator）    /// 
    public class Iterator : IIterator    {        private Collection _collection;        private int _current = 0;        private int _step = 1;        /// 
        /// 构造函数        /// 
        ///         public Iterator(Collection collection)        {            this._collection = collection;        }        /// 
        /// 第一个对象        /// 
        /// 
             public MessageModel First()        {            _current = 0;            return _collection[_current];        }        /// 
        /// 下一个对象        /// 
        /// 
             public MessageModel Next()        {            _current += _step;            if (!IsDone)            {                return _collection[_current];            }            else            {                return null;            }        }        /// 
        /// 当前对象        /// 
        public MessageModel CurrentMessageModel        {            get { return _collection[_current]; }        }        /// 
        /// 是否迭代完毕        /// 
        public bool IsDone        {            get { return _current >= _collection.Count ? true : false; }        }        /// 
        /// 步长        /// 
        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("
");        }    }}

　　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