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Abstract Factory Pattern

Abstract Factory Pattern 


Gamma Categorization: Creational Design Patten
Summary: When the object construction is complicated, needing multiple arguments, we should create a separate function (Factory Method) or class (Factory), which is responsible for the creation of the all object.

Problem examples

Suport of multiple databases
Multiple data sources: Serial port, ethernet port, device driver
Diferent report types

Solution

Abstract class
Generalized interface
A Factory creates instances of the concrete classes

Sample Code

The abstract factory

public interface IPhotoFactory
{
    IAnaloguePhoto CreateAnaloguePhoto();
    IDigitalPhoto CreateDigitalPhoto();
}


The abstract products

public interface IAnaloguePhoto
{
    string GetName();
}

public interface IDigitalPhoto
{
    string GetName();
}

The concrete factories
public class CanonFactory : IPhotoFactory
{
    public IAnaloguePhoto CreateAnaloguePhoto()
    {
        return new CanonAnaloguePhoto();
    }

    public IDigitalPhoto CreateDigitalPhoto()
    {
        return new CanonDigitalPhoto();
    }
}

public class NikonFactory : IPhotoFactory
{
    public IAnaloguePhoto CreateAnaloguePhoto()
    {
        return new NikonAnaloguePhoto();
    }

    public IDigitalPhoto CreateDigitalPhoto()
    {
        return new NikonDigitalPhoto();
    }
}

The concrete products

public class CanonAnaloguePhoto : IAnaloguePhoto
{
    public string GetName()
    {
        return "Canon Analogue Photo";
    }
}

public class CanonDigitalPhoto : IDigitalPhoto
{
    public string GetName()
    {
        return "Canon Digital Photo";
    } 
}

public class NikonAnaloguePhoto : IAnaloguePhoto
{
    public string GetName()
    {
        return "Nikon Analogue Photo";
    }
}

public class NikonDigitalPhoto : IDigitalPhoto
{
    public string GetName()
    {
        return "Nikon Digital Photo";
    } 
}

The client

public class PhotoClient
{
    public enum Brand { Canon, Nikon};

    private IPhotoFactory photoFactory;

    public PhotoClient(Brand brand)
    {
        switch (brand)
        {
            case Brand.Canon:
                photoFactory = new CanonFactory();
                break;
                case Brand.Nikon:
                photoFactory = new NikonFactory();
                break;
        }
    }

    public string GetAnaloguePhoto() => photoFactory.CreateAnaloguePhoto().GetName();
    public string GetDigitalPhoto() => photoFactory.CreateDigitalPhoto().GetName();
}

Usage

var photoClient = new PhotoClient(PhotoClient.Brand.Canon);
WriteLine(photoClient.GetAnaloguePhoto());
WriteLine(photoClient.GetDigitalPhoto());

photoClient = new PhotoClient(PhotoClient.Brand.Nikon);
WriteLine(photoClient.GetAnaloguePhoto());
WriteLine(photoClient.GetDigitalPhoto());

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