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