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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。
 

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


参考
http://www.dofactory.com/Patterns/PatternIterator.aspx


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