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Build watchOS Apps: Develop and Design by Mark Goody, Maurice Kelly

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Chapter 2. Anatomy of a watchOS App

Although a watchOS app may seem like a miniature version of an iOS app, the underlying architecture is subtly different. It isn’t essential to know the difference, but it can help in understanding how your watchOS app works and performs.

Apps and Extensions

A major limitation of the first generation of watchOS apps was that they could not run their code directly on the device. To circumvent this limitation, Apple allowed a watchOS app to run its code in the background on the user’s iPhone, by taking advantage of iOS extensions.

For the second generation of watchOS apps, Apple has retained the same extension-based execution model but with the distinction that the extension now runs on the watch instead of ...

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