Custom object factory extension for Unity

Question

I am using the Unity IoC container, and I need to intercept any calls to Resolve for a certain base interface, and run my own custom code to construct those types.

Answer 1

Update This answer was for Unity 1.2. For a solution that works with Unity 2, see my other answer.

---

OK, I have implemented the extension myself. In the builder I cache the object as I want it to be a singleton w.r.t my container. The reason for baseContext is that I want it to be cached in the top level container rather than in any child containers from which it was requested.

 public class FactoryMethodUnityExtension : UnityContainerExtension
 {
     private Func factory; 

     public FactoryMethodUnityExtension(Func factory)
     {
         this.factory = factory;
     }

     protected override void Initialize()
     {
         var strategy = new CustomFactoryBuildStrategy(factory, this.Context);
         Context.Strategies.Add(strategy, UnityBuildStage.PreCreation);             
     }
 } 

 public class CustomFactoryBuildStrategy : BuilderStrategy
 {
     private Func factory;
     private ExtensionContext baseContext;

     public CustomFactoryBuildStrategy(Func factory, ExtensionContext baseContext)
     {
        this.factory = factory;
        this.baseContext = baseContext;
     }

     public override void PreBuildUp(IBuilderContext context)
     {
         var key = (NamedTypeBuildKey)context.OriginalBuildKey;

         if (key.Type.IsInterface && typeof(T).IsAssignableFrom(key.Type))
         {
             object existing = baseContext.Locator.Get(key.Type);
             if (existing == null)
             {
                 // create it
                 context.Existing = factory(key.Type);
                 // cache it
                 baseContext.Locator.Add(key.Type, context.Existing);
             }
             else
             {
                 context.Existing = existing;
             }
         }
     }
 }

Adding the extension is quite simple:

MyFactory factory = new MyFactory();
container = new UnityContainer();
container.AddExtension(new FactoryMethodUnityExtension(factory.Create));