乐在其中设计模式(C#) - 备忘录模式(Memento Pattern)

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乐在其中设计模式(C#) - 备忘录模式(Memento Pattern)

作者：webabcd


介绍
在不破坏封装性的前提下，捕获一个对象的内部状态，并在该对象之外保存这个状态。这样以后就可将该对象恢复到保存的状态。


示例
有一个Message实体类，某个对象对它的操作有Insert()方法，只有在插入时间符合要求的情况下才能插入成功，因此要求可以保存和恢复Message对象的状态，插入失败后则恢复Message对象的状态，然后只更新时间，再次插入。

 

MessageModel

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

namespace Pattern.Memento
{
        /// <summary>
        /// Message实体类（Memento）
        /// </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; }
                }
        }
}

 

MessageModelCaretaker

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

namespace Pattern.Memento
{
        /// <summary>
        /// Memento管理者（Caretaker）
        /// </summary>
        public class MessageModelCaretaker
        {
                private MessageModel _messageModel;

                /// <summary>
                /// Message实体对象（Memento）
                /// </summary>
                public MessageModel MessageModel
                {
                        get { return _messageModel; }
                        set { _messageModel = value; }
                }
        }
}

 

SqlMessage

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

namespace Pattern.Memento
{
        /// <summary>
        /// Sql方式操作Message（Originator）
        /// </summary>
        public class SqlMessage
        {
                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; }
                }

                /// <summary>
                /// 插入Message
                /// </summary>
                /// <param name="mm">Message实体对象</param>
                /// <returns></returns>
                public bool Insert(MessageModel mm)
                {
                        // 秒数可以被5整除时，则执行插入操作
                        if (mm.PublishTime.Second % 5 == 0)
                        {
                                // 代码略
                                return true;
                        }
                        else
                        {
                                return false;
                        }
                }

                /// <summary>
                /// 保存Memento
                /// </summary>
                /// <returns></returns>
                public MessageModel SaveMemento()
                {
                        return new MessageModel(_message, _publishTime);
                }

                /// <summary>
                /// 恢复Memento
                /// </summary>
                /// <param name="mm"></param>
                public void RestoreMemento(MessageModel mm)
                {
                        this._message = mm.Message;
                        this._publishTime = mm.PublishTime;
                }
        }
}

 

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 Pattern.Memento;

public partial class Memento : System.Web.UI.Page
{
        protected void Page_Load(object sender, EventArgs e)
        {
                SqlMessage m = new SqlMessage();
                m.Message = "Message内容";
                m.PublishTime = DateTime.Now;

                MessageModelCaretaker mmc = new MessageModelCaretaker();
                mmc.MessageModel = m.SaveMemento();

                bool bln = false;
                while (!bln)
                {
                        bln = m.Insert(new MessageModel(m.Message, m.PublishTime));

                        Response.Write(m.Message + " " + m.PublishTime.ToString() + " " + bln.ToString());
                        Response.Write("<br />");

                        if (!bln)
                        {
                                System.Threading.Thread.Sleep(1000);

                                m.RestoreMemento(mmc.MessageModel);
                                m.PublishTime = DateTime.Now;
                        }
                }
        }
}

 

 

运行结果
Message内容 2007-5-23 21:32:13 False
Message内容 2007-5-23 21:32:14 False
Message内容 2007-5-23 21:32:15 True


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


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