C#设计模式--备忘录模式(Memento Pattern)

admin - 2008-6-13 15:42:00

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

附件: pattern.rar

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