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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.


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