Healthkit

This is a comprehensive reference for working with Apple's HealthKit framework in Swift 6.3 and iOS 26+. It covers the full lifecycle: checking availability, requesting authorization the right way (important for App Review), querying samples with the modern descriptor API, pulling statistics for aggregated data, and building time-series collections for charts. You also get practical guidance on writing samples, setting up background delivery so your app wakes when new data arrives, and recording workouts with HKWorkoutSession. The common mistakes section and unit reference tables are genuinely useful. If you're building anything that touches Apple Health data, whether it's displaying step counts, logging workouts, or syncing vitals in the background, this gives you the patterns you need without having to piece together Apple's scattered documentation.