Watch applications can run code in the same way that they run on an iOS device although the way in which they are uploaded to the watch is slightly different. Running code on the simulator is very different to running on a real device; the network and processor are much more limited than will be expected for a desktop class machine (or even an iOS device). As a result, testing on a real device is essential in order to test the full experience.

This chapter presented how watch applications and extensions are built, how they are packaged in the form of watch extensions and watch apps, and how they can share code with a parent application to avoid code duplication. The watch interface demonstrated how to transition between screens using segues to implement a watch extension of the iOS application that was created in the previous chapter.