13 Time to Watch Your WatchKit Code

This chapter introduces Apple Watch development with WatchKit by framing the Watch as a companion to the iPhone: a quick, glanceable “second display” that relies on the iOS app for heavier work. You’re guided to start a project in Xcode using the “iOS App with WatchKit App” template and reminded that every Watch app ships alongside an iOS app. Key differences from standard iOS development are highlighted, including the use of watch-specific UI classes (such as WKInterfaceLabel), the awake lifecycle method in place of viewDidLoad, and designing for two watch sizes with simple, focused interactions.

To make these ideas concrete, the chapter walks through building a Number Guessing Game for Apple Watch. The interface consists of two labels (for the current guess and status) and three buttons (+, −, and Make Guess). In code, two integers track the target number and the current guess; the target is randomly set between 1 and 120 during initialization in awake. IBActions for the buttons update the guess label as you increment or decrement, and the Make Guess action compares the guess to the target to display “Too Little!”, “Too Much!”, or “Correct!” in the status label. You connect IBOutlets and IBActions in Interface.storyboard, just as you would on iOS, but using WatchKit controls.

Finally, the chapter shows how to run the app on the Apple Watch simulator by changing the run target to the WatchKit App and selecting a watch size. While deploying to a physical Apple Watch takes extra steps, simulator testing is straightforward and lets you try the game immediately. The chapter closes with practice prompts—comparing iOS and watchOS development, adding features like counting attempts or bounding guesses, and thinking through optimal guessing strategies—reinforcing the core concepts of building and running a simple, responsive Watch app.

The final “Number Guessing Game” app in action!

The relationship between iOS and watchOS apps.

The second (and final) step to showing your WatchKit development files. Figure 13.3 The first step to showing your WatchKit development files

Figure 13.3 The first step to showing your WatchKit development files

The 3 views you will see in the “Interface.storyboard” file.

The 2 screen sizes of the Apple Watch. 38mm is the default size.

The final UI for the Number Guessing Game app.

Changing the Run Target

Changing the Run Target

Choosing the Apple Watch simulator

The final, running application!

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