This chapter was all about app extensions, and more specifically Today Extension. We started by exploring the basic anatomy of an extension in iOS. You learned that extensions are mostly view controllers that live separately from your main application. You learned how you can add an extension target to your project and how to run it in the Simulator.

Once we had the extension up and running, you learned how to share pieces of code and functionality between your application and the extension by adding a file to both targets. This left the app and widget in a state where they were unable to share data. We implemented data sharing by enabling App Groups, so that our app and its extension use a shared UserDefaults store.

With this powerful tool and knowledge under your belt, we're going to dive even deeper into the iOS Notification Center. We're going to implement the new notification features that iOS 10 implements through Notification Extensions.