Navigation Controller and OOP

Hi,

This to me sounds like an FAQ, but I haven't been able to find the answer. I have a navigation controller which is a variable in my app delegate.

Now suppose that from somewhere else in the app I need to push a view controller. I imagine three reasonable ways of doing.
1. Create a singleton-type global reference to the navigation controller
2. Access it through sharedApplication
3. Post a notification and let the delegate handle it.

Is there a 4th? And which one is best?

Thanks!

Sam