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Memento

Memento en C#

Memento es un patrón de diseño de comportamiento que permite tomar instantáneas del estado de un objeto y restaurarlo en el futuro.

El patrón Memento no compromete la estructura interna del objeto con el que trabaja, ni la información que se encuentra dentro de las instantáneas.

Uso del patrón en C#

Complejidad:

Popularidad:

Ejemplos de uso: El principio del patrón Memento puede cumplirse utilizando la serialización, que es bastante habitual en C#. Aunque no es la única forma ni la más efectiva de realizar instantáneas del estado de un objeto, permite almacenar copias de seguridad del estado mientras protege de otros objetos la estructura del originador.

Ejemplo conceptual

Este ejemplo ilustra la estructura del patrón de diseño Memento. Se centra en responder las siguientes preguntas:

  • ¿De qué clases se compone?
  • ¿Qué papeles juegan esas clases?
  • ¿De qué forma se relacionan los elementos del patrón?

Program.cs: Ejemplo conceptual

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;

namespace RefactoringGuru.DesignPatterns.Memento.Conceptual
{
    // The Originator holds some important state that may change over time. It
    // also defines a method for saving the state inside a memento and another
    // method for restoring the state from it.
    class Originator
    {
        // For the sake of simplicity, the originator's state is stored inside a
        // single variable.
        private string _state;

        public Originator(string state)
        {
            this._state = state;
            Console.WriteLine("Originator: My initial state is: " + state);
        }

        // The Originator's business logic may affect its internal state.
        // Therefore, the client should backup the state before launching
        // methods of the business logic via the save() method.
        public void DoSomething()
        {
            Console.WriteLine("Originator: I'm doing something important.");
            this._state = this.GenerateRandomString(30);
            Console.WriteLine($"Originator: and my state has changed to: {_state}");
        }

        private string GenerateRandomString(int length = 10)
        {
            string allowedSymbols = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
            string result = string.Empty;

            while (length > 0)
            {
                result += allowedSymbols[new Random().Next(0, allowedSymbols.Length)];

                Thread.Sleep(12);

                length--;
            }

            return result;
        }

        // Saves the current state inside a memento.
        public IMemento Save()
        {
            return new ConcreteMemento(this._state);
        }

        // Restores the Originator's state from a memento object.
        public void Restore(IMemento memento)
        {
            if (!(memento is ConcreteMemento))
            {
                throw new Exception("Unknown memento class " + memento.ToString());
            }

            this._state = memento.GetState();
            Console.Write($"Originator: My state has changed to: {_state}");
        }
    }

    // The Memento interface provides a way to retrieve the memento's metadata,
    // such as creation date or name. However, it doesn't expose the
    // Originator's state.
    public interface IMemento
    {
        string GetName();

        string GetState();

        DateTime GetDate();
    }

    // The Concrete Memento contains the infrastructure for storing the
    // Originator's state.
    class ConcreteMemento : IMemento
    {
        private string _state;

        private DateTime _date;

        public ConcreteMemento(string state)
        {
            this._state = state;
            this._date = DateTime.Now;
        }

        // The Originator uses this method when restoring its state.
        public string GetState()
        {
            return this._state;
        }
        
        // The rest of the methods are used by the Caretaker to display
        // metadata.
        public string GetName()
        {
            return $"{this._date} / ({this._state.Substring(0, 9)})...";
        }

        public DateTime GetDate()
        {
            return this._date;
        }
    }

    // The Caretaker doesn't depend on the Concrete Memento class. Therefore, it
    // doesn't have access to the originator's state, stored inside the memento.
    // It works with all mementos via the base Memento interface.
    class Caretaker
    {
        private List<IMemento> _mementos = new List<IMemento>();

        private Originator _originator = null;

        public Caretaker(Originator originator)
        {
            this._originator = originator;
        }

        public void Backup()
        {
            Console.WriteLine("\nCaretaker: Saving Originator's state...");
            this._mementos.Add(this._originator.Save());
        }

        public void Undo()
        {
            if (this._mementos.Count == 0)
            {
                return;
            }

            var memento = this._mementos.Last();
            this._mementos.Remove(memento);

            Console.WriteLine("Caretaker: Restoring state to: " + memento.GetName());

            try
            {
                this._originator.Restore(memento);
            }
            catch (Exception)
            {
                this.Undo();
            }
        }

        public void ShowHistory()
        {
            Console.WriteLine("Caretaker: Here's the list of mementos:");

            foreach (var memento in this._mementos)
            {
                Console.WriteLine(memento.GetName());
            }
        }
    }
    
    class Program
    {
        static void Main(string[] args)
        {
            // Client code.
            Originator originator = new Originator("Super-duper-super-puper-super.");
            Caretaker caretaker = new Caretaker(originator);

            caretaker.Backup();
            originator.DoSomething();

            caretaker.Backup();
            originator.DoSomething();

            caretaker.Backup();
            originator.DoSomething();

            Console.WriteLine();
            caretaker.ShowHistory();

            Console.WriteLine("\nClient: Now, let's rollback!\n");
            caretaker.Undo();

            Console.WriteLine("\n\nClient: Once more!\n");
            caretaker.Undo();

            Console.WriteLine();
        }
    }
}

Output.txt: Resultado de la ejecución

Originator: My initial state is: Super-duper-super-puper-super.

Caretaker: Saving Originator's state...
Originator: I'm doing something important.
Originator: and my state has changed to: oGyQIIatlDDWNgYYqJATTmdwnnGZQj

Caretaker: Saving Originator's state...
Originator: I'm doing something important.
Originator: and my state has changed to: jBtMDDWogzzRJbTTmEwOOhZrjjBULe

Caretaker: Saving Originator's state...
Originator: I'm doing something important.
Originator: and my state has changed to: exoHyyRkbuuNEXOhhArKccUmexPPHZ

Caretaker: Here's the list of mementos:
12.06.2018 15:52:45 / (Super-dup...)
12.06.2018 15:52:46 / (oGyQIIatl...)
12.06.2018 15:52:46 / (jBtMDDWog...)

Client: Now, let's rollback!

Caretaker: Restoring state to: 12.06.2018 15:52:46 / (jBtMDDWog...)
Originator: My state has changed to: jBtMDDWogzzRJbTTmEwOOhZrjjBULe

Client: Once more!

Caretaker: Restoring state to: 12.06.2018 15:52:46 / (oGyQIIatl...)
Originator: My state has changed to: oGyQIIatlDDWNgYYqJATTmdwnnGZQj

Memento en otros lenguajes

Patrones de diseño: Memento en Java Patrones de diseño: Memento en C++ Patrones de diseño: Memento en PHP Patrones de diseño: Memento en Python Patrones de diseño: Memento en Ruby Patrones de diseño: Memento en Swift Patrones de diseño: Memento en TypeScript Patrones de diseño: Memento en Go