Handle SwiftUI and CoreLocation with MVVM-Pattern - swift

Question

i am trying to implement SwiftUI and CoreLocation with the MVVM-Pattern. My LocationManager as Helper works fine. But how I can change the properties of my LocationViewModel? I am implemented my #ObservedObject of the LocationManager in LocationViewModel. Here is my problem.
I don't have a idea to implement properties they change on the fly. Nothing is changed in my LocationView. By pressing a Button anything works fine one time. But the LocationViewModel must change there properties on every change of the LocationManager.
In summary I would like to display the current user position.
// Location Manager as Helper
import Foundation
import CoreLocation
class LocationManager: NSObject, ObservableObject {
let locationManager = CLLocationManager()
let geoCoder = CLGeocoder()
#Published var location: CLLocation?
#Published var placemark: CLPlacemark?
override init() {
super.init()
self.locationManager.delegate = self
self.locationManager.desiredAccuracy = kCLLocationAccuracyBest
self.locationManager.requestWhenInUseAuthorization()
self.locationManager.startUpdatingLocation()
}
func geoCode(with location: CLLocation) {
geoCoder.reverseGeocodeLocation(location) { (placemark, error) in
if error != nil {
print(error!.localizedDescription)
} else {
self.placemark = placemark?.first
}
}
}
}
extension LocationManager: CLLocationManagerDelegate {
func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
guard let location = locations.first else { return }
DispatchQueue.main.async {
self.location = location
self.geoCode(with: location)
}
}
func locationManager(_ manager: CLLocationManager, didChangeAuthorization status: CLAuthorizationStatus) {
// TODO
}
}
// Location Model
import Foundation
import CoreLocation
struct Location {
var location: CLLocation = CLLocation()
var placemark: CLPlacemark = CLPlacemark()
}
// Location View Model
import SwiftUI
import CoreLocation
class LocationViewModel: ObservableObject {
#ObservedObject var locationManager: LocationManager = LocationManager()
#Published var location: Location
init() {
self.location = Location()
}
}
// Location View
import SwiftUI
struct LocationView: View {
#ObservedObject var locationViewModel: LocationViewModel = LocationViewModel()
var body: some View {
VStack(alignment: .leading) {
Text("Latitude: \(self.locationViewModel.location.location.coordinate.latitude.description)")
Text("Longitude: \(self.locationViewModel.location.location.coordinate.longitude.description)")
}
}
}
struct LocationView_Previews: PreviewProvider {
static var previews: some View {
LocationView()
}
}
Update
Now, I have set up my MapView.
But how I can receive the data of my LocationManager? The didUpdateLocations method is working in LocationManager.
All what I am trying to do goes wrong. I would like to set the region on my MapView based on the current user location. In UIKit it was very simple, but in SwiftUI it is freaky.
// Map View
import SwiftUI
import MapKit
struct MapView: UIViewRepresentable {
#ObservedObject var locationManager: LocationManager = LocationManager()
class Coordinator: NSObject, MKMapViewDelegate {
var parent: MapView
init(_ control: MapView) {
self.parent = control
}
}
func makeCoordinator() -> Coordinator {
Coordinator(self)
}
func makeUIView(context: Context) -> MKMapView {
let mapView = MKMapView(frame: .zero)
mapView.delegate = context.coordinator
return mapView
}
func updateUIView(_ mapView: MKMapView, context: Context) {
mapView.showsUserLocation = true
}
}
struct MapView_Previews: PreviewProvider {
static var previews: some View {
MapView()
}
}

Answer 1

SwiftUI 2
Use instead StateObject in this case
struct LocationView: View {
#StateObject var locationManager: LocationManager = LocationManager()
...
SwiftUI 1
Actually LocationViewModel is redundant here. As your LocationManager is a ObservableObject you can use it directly in your view, as below:
struct LocationView: View {
#ObservedObject var locationManager: LocationManager = LocationManager()
var body: some View {
VStack(alignment: .leading) {
Text("Latitude: \(locationManager.location.coordinate.latitude.description)")
Text("Longitude: \(locationManager.location.coordinate.longitude.description)")
}
}
}