Memento Pattern

Command Pattern 

Gamma Categorization: Behavioral Design Pattern
Summary: Without violating encapsulation, capture and externalize an object's internal state so that the object can be restored to this state later.

Sample Code

Problem: We want to apply several commands on the digital camera.

Code

public class DigitalCameraFirmware

{

    public string Name { get; set; }

    public byte[] Data { get; set; }

    public Memento SaveMemento()

    {

        return new Memento(Name, Data);

    }

    public void RestoreMemento(Memento memento)

    {

        this.Name = memento.Name;

        this.Data = memento.Data;

    }

}

public class Memento

{

    public string Name { get; private set; }

    public byte[] Data { get; private set; }

    public Memento(string name, byte[] data)

    {

        this.Name = name;

        this.Data = data;

    }

}

public class FirmwareMemory

{

    private Memento _memento;

    public Memento Memento

    {

        set { _memento = value; }

        get { return _memento; }

    }

}

Usage

var cameraFirmware = new DigitalCameraFirmware { Name = "v1.0", Data = new byte[1024] };

System.Console.WriteLine($"Current firmware version: {cameraFirmware.Name}");

FirmwareMemory memory = new FirmwareMemory();

memory.Memento = cameraFirmware.SaveMemento();

cameraFirmware.Name = "v2.0";

cameraFirmware.Data = new byte[1024];

System.Console.WriteLine($"Current firmware version: {cameraFirmware.Name}");

// something fails with the new firmware, so we want to restore the previous one

cameraFirmware.RestoreMemento(memory.Memento);

System.Console.WriteLine($"Current firmware version: {cameraFirmware.Name}");

Output

Current firmware version: v1.0

Current firmware version: v2.0

Current firmware version: v1.0