备忘录模式(Memento Pattern)

设计模式 - 吕震宇

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乐在其中设计模式(C#)

设计模式23：Memento Pattern (备忘录模式)

英文原文：http://www.dofactory.com/Patterns/PatternMemento.aspx

一、Memento Pattern (备忘录模式)

Define:Without violating encapsulation, capture and externalize an object's internal state so that the object can be restored to this state later.

定义：在不违反封装性，捕获和使得一个对象的内状态具体化，以至于这个对象可以被存储于这个状态之后。

二、UML类图

Memento  (Memento)

• stores internal state of the Originator object. The memento may store as much or as little of the originator's internal state as necessary at its originator's discretion.
• protect against access by objects of other than the originator. Mementos have effectively two interfaces. Caretaker sees a narrow interface to the Memento -- it can only pass the memento to the other objects. Originator, in contrast, sees a wide interface, one that lets it access all the data necessary to restore itself to its previous state. Ideally, only the originator that produces the memento would be permitted to access the memento's internal state.

Originator  (SalesProspect)

• creates a memento containing a snapshot of its current internal state.
• uses the memento to restore its internal state

Caretaker  (Caretaker)

• is responsible for the memento's safekeeping

• never operates on or examines the contents of a memento.

三、Memento Pattern (备忘录模式)实例代码

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

namespace Memento_Pattern
{
    /// <summary>

    /// MainApp startup class for Structural

    /// Memento Design Pattern.

    /// </summary>

    class MainApp
    {

        /// <summary>

        /// Entry point into console application.

        /// </summary>

        static void Main()
        {

            Originator o = new Originator();

            o.State = "On";



            // Store internal state

            Caretaker c = new Caretaker();

            c.Memento = o.CreateMemento();



            // Continue changing originator

            o.State = "Off";



            // Restore saved state

            o.SetMemento(c.Memento);



            // Wait for user

            Console.ReadKey();

        }

    }



    /// <summary>

    /// The 'Originator' class

    /// </summary>

    class Originator
    {

        private string _state;



        // Property

        public string State
        {

            get { return _state; }

            set
            {

                _state = value;

                Console.WriteLine("State = " + _state);

            }

        }



        // Creates memento

        public Memento CreateMemento()
        {

            return (new Memento(_state));

        }



        // Restores original state

        public void SetMemento(Memento memento)
        {

            Console.WriteLine("Restoring state...");

            State = memento.State;

        }

    }



    /// <summary>

    /// The 'Memento' class

    /// </summary>

    class Memento
    {

        private string _state;



        // Constructor

        public Memento(string state)
        {

            this._state = state;

        }



        // Gets or sets state

        public string State
        {

            get { return _state; }

        }

    }



    /// <summary>

    /// The 'Caretaker' class

    /// </summary>

    class Caretaker
    {

        private Memento _memento;



        // Gets or sets memento

        public Memento Memento
        {

            set { _memento = value; }

            get { return _memento; }

        }

    }
}

四、使用备忘录模式的实例代码

This real-world code demonstrates the Memento pattern which temporarily saves and then restores the SalesProspect's internal state.

临时保存和恢复SalesProspect的内部状态

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

namespace Memento_Pattern
{
    /// <summary>

    /// MainApp startup class for Real-World

    /// Memento Design Pattern.

    /// </summary>

    class MainApp
    {

        /// <summary>

        /// Entry point into console application.

        /// </summary>

        static void Main()
        {

            SalesProspect s = new SalesProspect();

            s.Name = "Noel van Halen";

            s.Phone = "(412) 256-0990";

            s.Budget = 25000.0;



            // Store internal state

            ProspectMemory m = new ProspectMemory();

            m.Memento = s.SaveMemento();



            // Continue changing originator

            s.Name = "Leo Welch";

            s.Phone = "(310) 209-7111";

            s.Budget = 1000000.0;



            // Restore saved state

            s.RestoreMemento(m.Memento);



            // Wait for user

            Console.ReadKey();

        }

    }



    /// <summary>

    /// The 'Originator' class

    /// </summary>

    class SalesProspect
    {

        private string _name;

        private string _phone;

        private double _budget;



        // Gets or sets name

        public string Name
        {

            get { return _name; }

            set
            {

                _name = value;

                Console.WriteLine("Name:  " + _name);

            }

        }



        // Gets or sets phone

        public string Phone
        {

            get { return _phone; }

            set
            {

                _phone = value;

                Console.WriteLine("Phone: " + _phone);

            }

        }



        // Gets or sets budget

        public double Budget
        {

            get { return _budget; }

            set
            {

                _budget = value;

                Console.WriteLine("Budget: " + _budget);

            }

        }



        // Stores memento

        public Memento SaveMemento()
        {

            Console.WriteLine("/nSaving state --/n");

            return new Memento(_name, _phone, _budget);

        }



        // Restores memento

        public void RestoreMemento(Memento memento)
        {

            Console.WriteLine("/nRestoring state --/n");

            this.Name = memento.Name;

            this.Phone = memento.Phone;

            this.Budget = memento.Budget;

        }

    }



    /// <summary>

    /// The 'Memento' class

    /// </summary>

    class Memento
    {

        private string _name;

        private string _phone;

        private double _budget;



        // Constructor

        public Memento(string name, string phone, double budget)
        {

            this._name = name;

            this._phone = phone;

            this._budget = budget;

        }



        // Gets or sets name

        public string Name
        {

            get { return _name; }

            set { _name = value; }

        }



        // Gets or set phone

        public string Phone
        {

            get { return _phone; }

            set { _phone = value; }

        }



        // Gets or sets budget

        public double Budget
        {

            get { return _budget; }

            set { _budget = value; }

        }

    }



    /// <summary>

    /// The 'Caretaker' class

    /// </summary>

    class ProspectMemory
    {

        private Memento _memento;



        // Property

        public Memento Memento
        {

            set { _memento = value; }

            get { return _memento; }

        }

    }
}

乐在其中设计模式(C#) - 备忘录模式(Memento Pattern)

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


OK
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