Handler for monitoring updates to the HealthKit store.
- iOS 9.0+
- watchOS 2.0+
If this property is set to
nil, the anchor query automatically stops as soon as it finishes calculating the initial results. If this property is not
nil, the query behaves similarly to the observer query: it continues to run, monitoring the HealthKit store. The system executes the update handler on a background queue whenever matching samples are saved to or deleted from the HealthKit store.