備忘錄模式(Memento Pattern)

介紹
在不破壞封裝性的前提下，捕獲一個對象的內部狀態，并在該對象之外保存這個狀態。這樣以后就可將該對象恢復到保存的狀態。

示例
有一個Message實體類，某個對象對它的操作有Insert()方法，只有在插入時間符合要求的情況下才能插入成功，因此要求可以保存和恢復Message對象的狀態，插入失敗后則恢復Message對象的狀態，然后只更新時間，再次插入。

　　MessageModel

using System; using System.Collections.Generic; using System.Text;namespace Pattern.Memento {/// <summary>/// Message實體類（Memento）/// </summary>public class MessageModel{/// <summary>/// 構造函數/// </summary>/// <param name="msg">Message內容</param>/// <param name="pt">Message發布時間</param>public MessageModel(string msg, DateTime pt){this._message = msg;this._publishTime = pt;}private string _message;/// <summary>/// Message內容/// </summary>public string Message{get { return _message; }set { _message = value; }}private DateTime _publishTime;/// <summary>/// Message發布時間/// </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實體對象（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內容/// </summary>public string Message{get { return _message; }set { _message = value; }}private DateTime _publishTime;/// <summary>/// Message發布時間/// </summary>public DateTime PublishTime{get { return _publishTime; }set { _publishTime = value; }}/// <summary>/// 插入Message/// </summary>/// <param name="mm">Message實體對象</param>/// <returns></returns>public bool Insert(MessageModel mm){// 秒數可以被5整除時，則執行插入操作if (mm.PublishTime.Second % 5 == 0){// 代碼略return true;}else{return false;}}/// <summary>/// 保存Memento/// </summary>/// <returns></returns>public MessageModel SaveMemento(){return new MessageModel(_message, _publishTime);}/// <summary>/// 恢復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內容";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;}}} }

　　運行結果

　　Message內容 2007-5-23 21:32:13 False
　　Message內容 2007-5-23 21:32:14 False
　　Message內容 2007-5-23 21:32:15 True

轉載于:https://www.cnblogs.com/taotaodetuer/p/6182189.html

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