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; } } } }