ContentView.swift

import SwiftUI
import HealthKit

struct ContentView: View {
    
    @EnvironmentObject var healthStore: HKHealthStore
    
    var body: some View {
        VStack {
            Image(systemName: "globe")
                .imageScale(.large)
                .foregroundColor(.accentColor)
            Text("Hello, world!")
        }
        .padding()
        .onAppear(){
            readHeartRate()
        }
    }
    
    //MARK: - Read heart rate
    
    private func readHeartRate(){
        let quantityType  = HKObjectType.quantityType(forIdentifier: .heartRate)!
        let sortDescriptor = NSSortDescriptor(key: HKSampleSortIdentifierStartDate, ascending: false)
        let sampleQuery = HKSampleQuery.init(sampleType: quantityType,
                                             predicate: get24hPredicate(),
                                             limit: HKObjectQueryNoLimit,
                                             sortDescriptors: [sortDescriptor],
                                             resultsHandler: { (query, results, error) in
            
            guard let samples = results as? [HKQuantitySample] else {
                print(error!)
                return
            }
            for sample in samples {
                let mSample = sample.quantity.doubleValue(for: HKUnit(from: "count/min"))
                print("Heart rate : \(mSample)")
            }
            
        })
        self.healthStore .execute(sampleQuery)
        
    }
    
    private func get24hPredicate() ->  NSPredicate{
        let today = Date()
        let startDate = Calendar.current.date(byAdding: .hour, value: -24, to: today)
        let predicate = HKQuery.predicateForSamples(withStart: startDate,end: today,options: [])
        return predicate
    }
}