fetchLatestHeartRateSample-closure.swift

/// When the completion is called, an other query is executed
/// to fetch the latest heart rate
self.fetchLatestHeartRateSample(completion: { sample in
  guard let sample = sample else {
    return
  }

  /// The completion in called on a background thread, but we
  /// need to update the UI on the main.
  DispatchQueue.main.async {

    /// Converting the heart rate to bpm
    let heartRateUnit = HKUnit(from: "count/min")
    let heartRate = sample
      .quantity
      .doubleValue(for: heartRateUnit)

    /// Updating the UI with the retrieved value
    self?.heartRateLabel.setText("\(Int(heartRate))")
  }
})