One of the new challenges of working with extensions such as WatchKit extensions is that since they run on a separate layer from your app you’ll need to add in a mechanism for data updates.
Here’s an open source library from Conrad Stoll of Mutual Mobile that allows you to easily create a bridge between an iOS extension and it’s application so you can easily pass data between the two locations called MMWormhole.
CFnotificationCenter is supported, and the end result is simple near instant updates on both sides when a message is sent using MMWormhole.
As stated on the Mutual Mobile Blog:
The library solves a key challenge common to developing Today and WatchKit extensions. The containing app typically owns all of the data that an extension might need to drive its UI, but transferring that data to the extension is somewhat cumbersome. Even more challenging is notifying the app or extension in real time that a change has been made that needs to be reflected in its user interface. MMWormhole solves both of those problems to put the focus back on building a rich extension.
This image from the readme shows MMWormhole in action:
You can read more about MMWormhole on the Mutual Mobile blog.
You can find the repository on Github here.
A nice library for easily sending data to/from your WatchKit and other extensions.