Decorator Pattern

Decorator Pattern 

Gamma Categorization: Structural Design Pattern
Summary: Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality.

Sample Code

Problem: We want extend our Camera object in order to allow it to use LiveView in addiction to taking photos.

Code

public abstract class Camera

{

    public string Name { get; set; }

    public abstract void TakePhoto();

}

public class DigitalCamera : Camera

{

    public override void TakePhoto() => System.Console.WriteLine($"Taking a photo with a {Name}.");

}

public abstract class AdvancedCamera : Camera

{

    public Camera Camera { get; protected set; }

    public AdvancedCamera(Camera camera) 

    {

        Camera = camera;

    }

    public abstract void LiveView();

}

public class AdvancedDigitalCamera : AdvancedCamera

{

    public AdvancedDigitalCamera(Camera camera) : base (camera) { }

    public override void TakePhoto() => Camera.TakePhoto();

    public override void LiveView() => System.Console.WriteLine($"Using LiveView in a {Camera.Name}.");

}

Usage

var camera = new AdvancedDigitalCamera(new DigitalCamera { Name = "Canon 70D" });

camera.TakePhoto();

camera.LiveView();

Output

Taking a photo with a Canon 70D.

Using LiveView with a Canon 70D.