Implement a singleton for iAd Banner

Do any one know how to correctly implement one instance for an ADBanner and share it for all view controllers in my开发者_运维百科 app ?

---

Pass the banner along as an instance variable as you create controllers?

Make the ad banner an instance variable on your app delegate?

Create a UIViewController category with an adBanner method that creates a static AdBanner if needed and returns it?