The Health Kit namespace, introduced in iOS 8, allows applications to record, track, and access health-related information to a common persistent store.

Provisioning, Permissions, and Profiles

To use Health Kit services, applications must be developed using an "Explicit App ID" and a provisioning profile that includes the explicit ID and Health Kit permissions.

In addition, applications must have an Entitlements.plist that contains the key com.apple.developer.healthkit of type Boolean with a value of true.

At runtime, the application must request access to the specific types of health data in which it is interested. The user will interact with a permissions dialog in the Health app that allows them fine-grained control over what health information they will allow.

var temperatureKey = HKQuantityTypeIdentifierKey.BodyTemperature;
var tempQuantityType = HKObjectType.GetQuantityType (temperatureKey);

var hks = new HKHealthStore ();
var success = await hks.RequestAuthorizationToShareAsync (new NSSet (new [] { tempQuantityType }), new NSSet ());
        
          

The result of the HealthKit.HKHealthStore.RequestAuthorizationtoShareAsync method indicates only that the user interacted with the permissions dialog, it does not indicate whether the user allowed any data sharing. For that, applications can use the HealthKit.HKHealthStore.GetAuthorizationStatus method:

var access = healthKitStore.GetAuthorizationStatus (HKObjectType.GetQuantityType (HKQuantityTypeIdentifierKey.HeartRate));
if (access.HasFlag (HKAuthorizationStatus.SharingAuthorized)) {
//...etc...
          

Creating and storing data

Once permissions have been granted, creating and storing data involves creating an HealthKit.HKSample of a particular HealthKit.HKSampleType and then calling HealthKit.HKHealthStore.SaveObject or HealthKit.HKHealthStore.SaveObjectAsync.

Exception-handling differences between async and non-async methods

Apple's philosophy regarding attempts to store or read non-permitted information is that such attempts should not cause runtime exceptions. Rather, methods such as HealthKit.HKHealthStore.RequestAuthorizationToShare and HealthKit.HKStore.SaveObject are defined with completion callback handlers that are passed a non-null Foundation.NSError argument in the case of an error. Application developers using such methods should take special care to check for success, as it is highly likely that users will be cautious about access to their health data.

In contrast, Xamarin's asynchronous versions of such methods (such as HealthKit.HKHealthStore.RequestAutorizationToShareAsync and HealthKit.HKHealthStore.SaveObjectAsync) will throw an Foundation.NSErrorException on failure or if the method is not allowed by the end user.

//Apple's philosophy: no exception
var myCurrentTemp = HKQuantity.FromQuantity (HKUnit.DegreeFahrenheit, 98.6);
var tempSample = HKQuantitySample.FromType (tempQuantityType, myCurrentTemp, new NSDate (), new NSDate (), new NSDictionary());

hks.SaveObject(tempSample, (success, error) => {
	if(error != null)
	{
   //...etc...
          

//Xamarin's philosophy: Lack of permissions raises exception
protected async void StoreAsync(HKHealthStore store, HKQuantitySample sample)
{
	try
	{
		var success = await store.SaveObjectAsync (sample);

	}catch(NSErrorException x)
	{
		Console.WriteLine (x);
	}
}
          

There are several types of HealthKit.HKObjecTypes:

HealthKit.HKCharacteristicType objects represent static characterics of the user, such as date of birth or blood type (see HealthKit.HKCharacteristicTypeIdentifierKey), while HealthKit.HKSampleType objects represent data that are sampled over time. As of iOS 8, there is only one type of HealthKit.HKCategorySample, which is HealthKit.HKCategoryTypeIdentifierKey.SleepAnalysis. The large majority of Health Kit data types are defined in HealthKit.HKQuantityTypeIdentifierKey.

Manipulating data samples involves both an HealthKit.HKSampleType object and an HealthKit.HKSample to carry the data:

HealthKit.HKQuantitySamples may refer to an instantaneous measurement, in which case their HealthKit.HKQuantitySample.StartDate and HealthKit.HKQuantitySample.EndDate properties should be set to the same value. Other samples, such as step count, are measured over time and the start and end time should be set appropriately.

Data may have metadata associated with it. There are a number of predefined metadata keys in HealthKit.HKMetadataKey, but application developers are encouraged to created their own keys for metadata as well.

Units of measurement and conversion

Health Kit supports units of measurement in the categories of mass, length, volume, and energy. This support includes conversion of values between measurement systems (for instance, if a user prefers Fahrenheit degrees but has a sensor that reports its data in Celsius). This is automatically supported within the Health app, but explicit conversions are also possible, as shown in the following example:

var myFahrenheitTemp = HKQuantity.FromQuantity (HKUnit.DegreeFahrenheit, 98.6);
var myCelsiusTemp = myFahrenheitTemp.GetDoubleValue (HKUnit.DegreeCelsius);