How do you create Static Factories?

Question

I have a series of Factory objects I wish to expose trough a "root" utility (object). This root utility is in-and-of itself...a factory. As a utility object, I wish to implement it as a static class. However, isn't possible using my current design...as you cannot implement static members in an interface.

So...

MY QUESTION IS: How can I alter the classes below to get the static factory affect above?

THE CODE LOOKS LIKE:

public interface IFactory
{
    I Create<I>();

    IFactoryTransform Transformer { get; }
    IFactoryDataAccess DataAccessor { get; }
    IFactoryValidator Validator { get; }
}

public static class Factory : IFactory
{
    static Factory()
    {

        Transformer = new FactoryTransform();
        DataAccessor = new FactoryDataAccess();
        Validator = new FactoryValidator();
    }

    public I Create<I>()
    {
        var model = typeof(I);

        // Activation code will go here...

        throw new NotSupportedException("Type " + model.FullName + " is not supported.");
    }

    public IFactoryDataAccess DataAccessor { get; private set; }
    public IFactoryTransform Transformer { get; private set; }
    public IFactoryValidator Validator { get; private set; }
}

you can check this post http://miroprocessordev.blogspot.com/2011/12/design-patterns-series-7-singleton.html to create a singleton pattern and I think you don't have to instantiate your objects in the constructor — Amir Ismail, Aug 05 '12 at 12:36

score 4 · Accepted Answer · answered Aug 05 '12 at 12:42

You can move your static keyword from Factory class to one level up. For example you can have a static class Utils, where you have a singleton property MyFactory.

public static class Utils
{
    public static IFactory MyFactory {get; private set}
    static Utils()
    {  
        MyFactory = new Factory();
    }
}

//usage
var myInterface = Utils.MyFactory.Create<IMyInterfrace>()

That said, I would probably use DI instead of the factories and IoC container to manage lifetime of the objects.

score 0 · Answer 2 · answered Aug 05 '12 at 12:32

0

It is not possible that a static class is inheriting from an interface. I think what you really want is a singleton lifecycle factory.

answered Aug 05 '12 at 12:32

Rookian

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Could you please post a simple example? – Prisoner ZERO Aug 05 '12 at 12:34
Is this more an Abstract Factory-type concept? Take a look here: http://stackoverflow.com/questions/1993397/abstract-factory-pattern-on-top-of-ioc – David Osborne Aug 05 '12 at 12:38

score 0 · Answer 3 · answered Aug 05 '12 at 12:40

why don't use Microsoft unity and dependency injection it is a better practice than manage yourself a static factory: http://msdn.microsoft.com/en-us/library/ff649614.aspx it will be unity framework that will instantiate for you all object

IUnityContainer myContainer = new UnityContainer();
FactoryDataAccess da= new FactoryDataAccess();
myContainer.RegisterInstance<IFactoryDataAccess >(da);

when you call it, it will use FactoryDataAccess instance :

IFactoryDataAccess myServiceInstance = myContainer.Resolve<IFactoryDataAccess >();

How do you create Static Factories?

3 Answers3