createquery.swift

var anchor: HKQueryAnchor?

    func createHeartRateStreamingQuery(_ workoutStartDate: Date) -> HKQuery? {
        
        guard let heartRateType: HKQuantityType = HKQuantityType.quantityType(forIdentifier: .heartRate) else {
            print("Could not get heart rate type")
            return nil
        }
        let datePredicate = HKQuery.predicateForSamples(withStart: workoutStartDate,
                                                    end: nil,
                                                    options: .strictEndDate)
        let compoundPredicate = NSCompoundPredicate(andPredicateWithSubpredicates: [datePredicate])
        
        let heartRateQuery = HKAnchoredObjectQuery(type: heartRateType,
                                                   predicate: compoundPredicate,
                                                   anchor: nil,
                                                   limit: Int(HKObjectQueryNoLimit))
        { (query, sampleObjects, deletedObjects, newAnchor, error) in
            guard let newAnchor = newAnchor,
                  let sampleObjects = sampleObjects else {
                    return
            }
            self.anchor = newAnchor
        }
        
        heartRateQuery.updateHandler = {(query, sampleObjects, deletedObjects, newAnchor, error) -> Void in
            guard let newAnchor = newAnchor,
                let sampleObjects = sampleObjects else {
                    return
            }
            self.anchor = newAnchor
        }
        return heartRateQuery
    }