Chain of Responsibility

Chain of Responsibility Pattern 

Gamma Categorization: Structural Design Pattern
Summary: Encapsulate a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support undoable operations.

Sample Code

Problem: We want to create a proxy class to intercept the server connection.

Code

public class Photo

{

    public string Name { get; set; }

    public int Exposure { get; set; }

    public int Saturation { get; set; }

    public int Contrast { get; set; }

    public Photo(string name)

    {

        this.Name = name;

        this.Exposure = this.Saturation = this.Contrast = 0;

    }

}

public class PhotoModifier

{

    protected Photo photo;

    protected PhotoModifier next;

        

    public PhotoModifier(Photo photo)

    {

        this.photo = photo;

    }

    public void Add(PhotoModifier photoModifier)

    {

        if (next != null) 

            next.Add(photoModifier);

        else 

            next = photoModifier;

    }

    public virtual void Handle() => next?.Handle();        

}

public class AddOneStopExposure : PhotoModifier

{

    public AddOneStopExposure(Photo photo) : base (photo) {}

    public override void Handle()

    {

        System.Console.WriteLine("Increasing exposure.");

        photo.Exposure += 1;

        base.Handle();

    }

}

public class AddContrast : PhotoModifier

{

    public AddContrast(Photo photo) : base (photo) {}

    public override void Handle()

    {

        System.Console.WriteLine("Increasing constrast.");

        photo.Contrast += 1;

        base.Handle();

    }

}

Usage

var photo = new Photo("IMG_01");

var modifierBase = new PhotoModifier(photo);

modifierBase.Add(new AddOneStopExposure(photo));

modifierBase.Add(new AddContrast(photo));

modifierBase.Handle();

System.Console.WriteLine($"Photo: {photo.Name}, Exposure: {photo.Exposure}, Contrast: {photo.Contrast}, Saturation: {photo.Saturation}");

Output

Increasing exposure.
Increasing constrast.
Photo: IMG_01, Exposure: 1, Contrast: 1, Saturation: 0