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HealthKit Extensions

Extensions for Apple HealthKit to make the API easier to use. This includes:

  • Dedicated types for all sample types
  • Automatic unit conversions and metadata handling
  • A wrapper around HKHealthStore for easier querying and saving

Samples

Creating samples

Normally, one would create HKSample samples manually:

let metadata: [String: Any] = [HKMetadataKeySexualActivityProtectionUsed : true]
let sample = HKCategorySample(
    type: .init(.sexualActivity), 
    value: HKCategoryValue.notApplicable.rawValue, 
    start: .now, 
    end: .now,
    metadata: metadata)

Using the extensions, this becomes much easier:

let activity = SexualActivity(protectionUsed: true, start: .now, end: .now)

The types automatically use the correct sample identifier, and set the correct value and metadata fields for the specific type. The created HealthKit sample can be accessed as a property:

let object: HKObject = activity.object
let sample: HKSample = activity.sample
let category: HKCategorySample = activity.categorySample

Category samples

Category samples either have a value (usually an enum) or don't allow a value. Depending on the type, a value can be provided in the constructor:

let result = PregnancyTestResult(value: .positive, start: .now, end: .now)
let pregnancy = Pregnancy(start: now, end: now)

Whenever a category sample requires or allows additional metadata fields, it can be set using the constructor. The types also expose these fields as properties.

let sample = SexualActivity(protectionUsed: true, start: .now, end: .now)
let wasSafe = sample.protectionUsed // Bool?

Quantity samples

HKQuantitySample types only include a quantity, which can be given to the constructor as a value or a quantity:

let value = BodyFatPercentage(value: 10.3, start: .now, end: .now)
let quantity = HKQuantity(unit: .precent(), doubleValue: 10.3)
let value = BodyFatPercentage(quantity: quantity, start: .now, end: .now)

When only the value is provided, then it is interpreted in the defaultUnit for the type.

Cumulative and discrete samples

Depending on the quantity, there are different properties exposed for samples that are either cumulative or discrete. Cumulative samples have an aggregationStyle == .cumulative and provide the sumQuantity property.

let sample = ActiveEnergyBurned(...)
let sum = sample.sumQuantity

Discrete samples have aggregationStyle values of .discreteArithmetic, .discreteTemporallyWeighted, or .discreteEquivalentContinuousLevel and expose the properties averageQuantity, maximumQuantity, minimumQuantity, mostRecentQuantity, and mostRecentQuantityDateInterval.

let sample = CyclingPower(...)
let max = sample.maximumQuantity

Custom UUIDs

It's possible to assign custom UUIDs directly in the constructor:

let uuid = UUID()
let sample = SexualActivity(protectionUsed: true, start: .now, end: .now, uuid: uuid)
print(sample.preferredUUID == uuid) // true

Metadata Keys

When manipulating and accessing HKSample and HKObject types, there are many metadata keys required to get certain properties. Most of the time, it's unnecessary to access metadata directly, since the types provide the expected fields as properties or constructor arguments. The library still provides a more convenient way to interact with metadata:

var metadata = Metadata() // typealias for [String : Any]
metadata.menstrualCycleStart = true // Sets HKMetadataKeyMenstrualCycleStart
let cycleStart: Bool = metadata.menstrualCycleStart

This shorthand format works for all known keys defined in the HKMetadataKey enum.

Queries

Interacting with the HKHealthStore can be simplified by wrapping it in a HealthStore:

let store = HealthStore(wrapping: HKHealthStore())

It's then possible to use all the convenience functions on HealthStore, or (for complex queries) just use the store: HKHealthStore property as oine normally would.

The HealthStore functions make a lot of use of async/await instead of completion handlers, and use the convenience sample types described above.

Requesting permissions

Before saving or reading samples from HealthKit, the permissions must be obtained:

try await store.requestAuthorization(
    toShare: Vomiting.self, SoreThroat.self,
    read: SkippedHeartbeat.self, SleepChanges.self)

It's also possible to pass an array of types instead of variadic arguments. To check the authorization status, there are also overloads:

let status = store.authorizationStatus(for: SexualActivity.self)

User characteristics

All user characteristic functions of HKHealthStore have been mapped to HealthStore, but directly returning the value instead of the object.

let sex: HKBiologicalSex = try store.biologicalSex()

Saving to the health store

There are function overloads to directly pass objects to the health store:

let sample = SexualActivity(...)
try await store.save(sample)

Reading samples

There are functions to directly retrieve typed objects for quantities, category samples and correlations:

let samples: [Vo2Max] = try await store.samples(
    from: Date.distantPast,
    to: Date.now,
    sortedBy: .ascendingStartDate,
    limitedTo: 100)

Workouts

let runs = try await store.workouts(
    activityType: .running,
    from: Date.distantPast,
    to: Date.now,
    sortedBy: .ascendingStartDate,
    limitedTo: 100)

Workout samples

let workout: HKWorkout = runs.first!
let heartRates: [HeartRate] = try await store
    .samples(associatedWith: workout)

The function automatically queries for condensed samples, and returns all samples at once.

Workout route and locations

let route = try store.route(associatedWith: workout)
let locations = try store.locations(associatedWith: route!)