Cook Computing

Configuring a Factory with Unity

I've just started using Unity (v1.2) and in one scenario I need to be able to configure Unity with a factory for a type, rather than default to Unity creating an object of the type configured for the requested type. In my case the object implementing the interface is a Remoting proxy but say, for example, I have interface IFoo implemented by class Foo and I want instances of IFoo returned by Unity to be instances of Foo created by a factory class:

interface IFoo
{
  void DoFoo();
}

class Foo : IFoo
{
  public void DoFoo()
  {
    Console.WriteLine("DoFoo: CreatedBy = {0}", CreatedBy);
  }
  public string CreatedBy { get; set; }
}

class FooFactory
{
  static public IFoo CreateInstance()
  {
    Console.WriteLine("CreateInstance");
    var foo = new Foo();
    foo.CreatedBy = "Factory";
    return foo;
  }
}

The solution is to use Unity's StaticFactoryExtension. After creating the container, add the extension to the container and then register the factory:

using Microsoft.Practices.Unity;
using Microsoft.Practices.Unity.StaticFactory;
// ...
IUnityContainer container = new UnityContainer();
container.AddNewExtension<StaticFactoryExtension>(); 
IStaticFactoryConfiguration config
  = container.Configure<IStaticFactoryConfiguration>();
config.RegisterFactory<IFoo>(unity => FooFactory.CreateInstance());

Finally we can request an instance of IFoo from the container:

IFoo foo = container.Resolve<IFoo>();
foo.DoFoo();

The following assembly references are required:

• Microsoft.Practices.ObjectBuilder2
• Microsoft.Practices.Unity
• Microsoft.Practices.Unity.StaticFactory