二十四种设计模式：备忘录模式(Memento Pattern)

备忘录模式(Memento Pattern)

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