swiftUI Mapkit and Corelocation causing problems - swiftui

Question

I'm reposting my question of yesterday and now adding a clean code example to demonstrate the problem
I have a MyCustomMapView, embedding a MKMApView and it starts at a fixed location. I have a function called gotoCoordinate, which accepts a coordinate and then navigates the mapview's center to that coordinate.
In the sample code that can be simulated by clicking on the red button labelleing "Click here to change map position".
This all works great. Until....
in the app I'm working on I also need to have a user location so I have a LocationViewModel handling the request. Once you have given request to access your location, click the button no longer moves the center of the map to that new coordinate.
Once you comment the #StateObject var locationViewModel = LocationViewModel() it is working again.
So it seems that once you are using a location manager with a delegate the map no longer moves when changing it's region
Is this a bug or am I doing something wrong?
import SwiftUI
struct ContentView: View {
#StateObject var locationViewModel = LocationViewModel()
var body: some View {
switch locationViewModel.authorizationStatus {
case .notDetermined:
AnyView(RequestLocationView())
.environmentObject(locationViewModel)
case .restricted:
ErrorView(errorText: "Location use is restricted.")
case .denied:
ErrorView(errorText: "The app does not have location permissions. Please enable them in settings.")
default:
EmptyView()
}
GeometryReader { geometry in
DisplayMapView(size:geometry.size)
}
}
}
import SwiftUI
import CoreLocation
import MapKit
struct MyCustomMapView: UIViewRepresentable {
var map = MKMapView() // << constructor contract !!
let coordinate: CLLocationCoordinate2D = CLLocationCoordinate2D(latitude:31,longitude: -86 )
func makeUIView(context: Context) -> MKMapView {
map.delegate = context.coordinator
map.showsUserLocation = true
map.showsCompass = true
let region = MKCoordinateRegion(
center: CLLocationCoordinate2D(latitude: coordinate.latitude,longitude: coordinate.longitude),
span: MKCoordinateSpan(latitudeDelta: 0.1, longitudeDelta: 0.1))
map.setRegion(region, animated: true)
return map
}
func gotoCoordinate(_ newCoordinate: CLLocationCoordinate2D ){
let region = MKCoordinateRegion(center: newCoordinate, span: MKCoordinateSpan(latitudeDelta: 0.2, longitudeDelta: 0.2))
map.setRegion(region, animated: true)
}
func updateUIView(_ uiView: MKMapView, context: Context) {
}
func makeCoordinator() -> MyCustomMapView.Coordinator {
return MyCustomMapView.Coordinator(parent1: self)
}
final class Coordinator: NSObject, MKMapViewDelegate {
var parent:MyCustomMapView
init(parent1:MyCustomMapView){
parent = parent1
}
}//class Coordinator
}
import SwiftUI
import CoreLocation
import MapKit
struct DisplayMapView: View {
#Environment(\.presentationMode) var presentationMode
var size: CGSize
var startCoordinate: CLLocationCoordinate2D = CLLocationCoordinate2D(latitude:40.741895,longitude: -73.989308)
var map = MyCustomMapView()
var body: some View {
ZStack(alignment:.top){
map
VStack(alignment:.leading){
HStack {
HStack {
Text("Click here to change map position")
.onTapGesture(){
map.gotoCoordinate(startCoordinate)
}
}
.padding(EdgeInsets(top: 8, leading: 6, bottom: 8, trailing: 6))
.foregroundColor(.black)
.background(Color(.red))
.cornerRadius(10.0)
}
}.padding(.top,50).padding(.leading,20).padding(.trailing,20)
}.ignoresSafeArea()
}
}
import Foundation
import SwiftUI
import CoreLocation
class LocationViewModel: NSObject, ObservableObject, CLLocationManagerDelegate {
#Published var authorizationStatus: CLAuthorizationStatus
#Published var lastSeenLocation: CLLocation?
#Published var currentPlacemark: CLPlacemark?
private let locationManager: CLLocationManager
static let shared = LocationViewModel()
override init() {
locationManager = CLLocationManager()
authorizationStatus = locationManager.authorizationStatus
super.init()
locationManager.delegate = self
locationManager.desiredAccuracy = kCLLocationAccuracyBest
locationManager.distanceFilter = 0.4
locationManager.startUpdatingLocation()
}
func requestPermission() {
locationManager.requestWhenInUseAuthorization()
}
func locationManagerDidChangeAuthorization(_ manager: CLLocationManager) {
authorizationStatus = manager.authorizationStatus
}
func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
lastSeenLocation = locations.first
}
}
struct RequestLocationView: View {
#EnvironmentObject var locationViewModel: LocationViewModel
var body: some View {
VStack(spacing:50) {
Image(systemName: "location.circle")
.resizable()
.frame(width: 100, height: 100, alignment: .center)
.foregroundColor(Color.init(red: 0.258, green: 0.442, blue: 0.254))
Button(action: {
locationViewModel.requestPermission()
}, label: {
Label(LocalizedStringKey("allowLocationAccess"), systemImage: "location")
})
.padding(10)
.foregroundColor(.white)
.background(.green)
.clipShape(RoundedRectangle(cornerRadius: 8))
Text("We need your permission to give you the best experience.")
.foregroundColor(.gray)
.font(.caption)
}
}
}
struct ErrorView: View {
var errorText: String
var body: some View {
VStack {
Image(systemName: "xmark.octagon")
.resizable()
.frame(width: 100, height: 100, alignment: .center)
Text(errorText)
}
.padding()
.foregroundColor(.white)
.background(Color.red)
.clipShape(RoundedRectangle(cornerRadius: 12))
}
}

Answer 1

Declare your coordinates as a stateful variable, either as #State or as #Published within an observable object:
struct DisplayMapView: View {
#State var coordinates = CLLocationCoordinate2D(latitude:40.741895,longitude: -73.989308)
Then pass the coordinates in as an argument to your view - no need to store your view as a variable:
ZStack(alignment: .top) {
MyMapView(coordinates: coordinates)
VStack(alignment: .leading) {
// etc.
Then you’ll need to do some rejigging in your UIViewRepresentable. You mustn't retain map as a separate instance outside makeUIView and updateUIView - SwiftUI structs can be recreated at will, so that would release your MKMapView instance and create a new one. Instead, the object returned by makeUIView is retained for you by the system. You do need to declare a variable that will accept the coordinates argument above, and then respond to any changes in it in updateUIView.
struct MyMapView: UIViewRepresentable {
var coordinates: CLLocationCoordinate2D
func makeUIView(context: Context) -> MKMapView {
let map = MKMapView()
map.delegate = context.coordinator
// etc.
return map
}
func updateUIView(_ uiView: MKMapView, context: Coordinator) {
let region = MKCoordinateRegion(center: coordinates, span: MKCoordinateSpan(latitudeDelta: 0.2, longitudeDelta: 0.2))
uiView.setRegion(region, animated: true)
}
}
Now, when the user taps, instead of calling a function inside your view, you update the DisplayMapView’s coordinates variable and the UIViewRepresentable’s update logic should redraw the map in the correct position.