workoutbuilder.swift

func workoutBuilder(_ workoutBuilder: HKLiveWorkoutBuilder, didCollectDataOf collectedTypes: Set<HKSampleType>) {
    for type in collectedTypes {
        guard let quantityType = type as? HKQuantityType else {
            return
        }
        
        switch quantityType {
        case HKQuantityType.quantityType(forIdentifier: .heartRate):
            guard let statistics = workoutBuilder.statistics(for: quantityType),
                let value = statistics.mostRecentQuantity()?.doubleValue(for: heartRateUnit)
                else {
                break
            }
            self.updateHeartRate(Int(value))
        default:
            break
        }
    }
}