The release of watchOS 2 brings significant changes with it. One of those changes is the ability to easily communicate with a counterpart. There are scenarios in which the watchOS app and the parent iOS app need to communicate for one reason or another. To make this communication easier, Apple created the Watch Connectivity framework. In this tutorial, I’m going to teach you how to send messages from a watchOS app to its parent iOS app, and vice versa.
Source files for the Tuts+ tutorial: watchOS 2: Communicating With a Counterpart
Read this tutorial on Tuts+