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 MonoTouch.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 MonoTouch.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 MonoTouch.HealthKit.HKSample of a particular MonoTouch.HealthKit.HKSampleType and then calling MonoTouch.HealthKit.HKHealthStore.SaveObject or MonoTouch.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 MonoTouch.HealthKit.HKHealthStore.RequestAuthorizationToShare and MonoTouch.HealthKit.HKStore.SaveObject are defined with completion callback handlers that are passed a non-null MonoTouch.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 MonoTouch.HealthKit.HKHealthStore.RequestAutorizationToShareAsync and MonoTouch.HealthKit.HKHealthStore.SaveObjectAsync) will throw an MonoTouch.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 MonoTouch.HealthKit.HKObjecTypes:

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

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

MonoTouch.HealthKit.HKQuantitySamples may refer to an instantaneous measurement, in which case their MonoTouch.HealthKit.HKQuantitySample.StartDate and MonoTouch.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 MonoTouch.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);