无法将 Tap Gesture Recognizer 添加到 SwiftUI MKMapView UIViewRepresentable

Question

I have a SwiftUI app with SwiftUI life cycle and I'm trying to get a tap gesture to work in an MKMapView. I can't seem to get the reference to the map correctly. All I want to do in this subsection is tap the map and add an annotation. I would then also use the coordinates of the annotation.

Here's the code.

struct MapView: UIViewRepresentable {

    typealias UIViewType = MKMapView
    @State private var myMapView: MKMapView?

    class Coordinator: NSObject, MKMapViewDelegate {
        var control: MapView
        let parent = MapView()
    
        let sfCoord = CLLocationCoordinate2D(latitude: 37.7749, longitude: -122.4194)

        init(_ control: MapView) {
            self.control = control
        }
    
        func mapView(_ mapView: MKMapView, didAdd views: [MKAnnotationView]) {
            if let annotationView = views.first {
                if let annotation = annotationView.annotation {
                    if annotation is MKUserLocation {
                        let region = MKCoordinateRegion(center: annotation.coordinate, latitudinalMeters: 2000, longitudinalMeters: 2000)
                        mapView.setRegion(region, animated: true)
                    }
                }
            }
        }//did add
    
        @objc func addAnnotationOnTapGesture(sender: UITapGestureRecognizer) {
            if sender.state == .ended {
                print("in addAnnotationOnTapGesture")
                let point = sender.location(in: parent.myMapView)
                print("point is \(point)")
                let coordinate = parent.myMapView?.convert(point, toCoordinateFrom: parent.myMapView)
                print("coordinate?.latitude is \(String(describing: coordinate?.latitude))")
                let annotation = MKPointAnnotation()
                annotation.coordinate = coordinate ?? sfCoord
                annotation.title = "Start"
                parent.myMapView?.addAnnotation(annotation)
            }
        }
    }//coord

    func makeUIView(context: Context) -> MKMapView {
        let map = MKMapView()
        map.showsUserLocation = true
        map.delegate = context.coordinator
    
        DispatchQueue.main.async {
            self.myMapView = map
        }
    
        let gRecognizer = UITapGestureRecognizer(target: context.coordinator, action: #selector(Coordinator.addAnnotationOnTapGesture(sender:)))
        map.addGestureRecognizer(gRecognizer)

        return map
    }

    func makeCoordinator() -> Coordinator {
        Coordinator(self)
    }

    func updateUIView(_ uiView: MKMapView, context: Context) {

    }
}//struct MapView

And the LocationManager for reference:

class LocationManager: NSObject, ObservableObject {
    private let locationManager = CLLocationManager()
    @Published var location: CLLocation? = nil

    override init() {
        super.init()
        self.locationManager.delegate = self
        self.locationManager.desiredAccuracy = kCLLocationAccuracyBest
        self.locationManager.distanceFilter = kCLDistanceFilterNone
        self.locationManager.requestWhenInUseAuthorization()
        self.locationManager.startUpdatingLocation()
    }
}

extension LocationManager: CLLocationManagerDelegate {
    
    func locationManager(_ manager: CLLocationManager, didChangeAuthorization status: CLAuthorizationStatus) {
        print(status)
    }
    
    func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
        guard let location = locations.last else { return }
    
        self.location = location
    }
}//extension

And finally the ContentView:

struct ContentView: View {

    @ObservedObject var locationManager = LocationManager()

    var body: some View {
        MapView()
    }
}

Tapping the map shows a console output like this:

in addAnnotationOnTapGesture

point is (156.0, 515.6666564941406)

coordinate?.latitude is nil

Any guidance would be appreciated. Xcode 12.5 iOS 14.5

Answer 1

In your Coordinator , you have two references to MapView s. One ( control ) is set in init and represents the actual view that you want. The other ( parent ) is defined within your Coordinator and is not actually part of the view hierarchy. Therefore, when you try to get a coordinate from it, it returns nil . You can change all of the references to control and it works:

class Coordinator: NSObject, MKMapViewDelegate {
    var control: MapView

    let sfCoord = CLLocationCoordinate2D(latitude: 37.7749, longitude: -122.4194)

    init(_ control: MapView) {
        self.control = control
    }

    func mapView(_ mapView: MKMapView, didAdd views: [MKAnnotationView]) {
        if let annotationView = views.first {
            if let annotation = annotationView.annotation {
                if annotation is MKUserLocation {
                    let region = MKCoordinateRegion(center: annotation.coordinate, latitudinalMeters: 2000, longitudinalMeters: 2000)
                    mapView.setRegion(region, animated: true)
                }
            }
        }
    }//did add

    @objc func addAnnotationOnTapGesture(sender: UITapGestureRecognizer) {
        if sender.state == .ended {
            print("in addAnnotationOnTapGesture")
            let point = sender.location(in: control.myMapView)
            print("point is \(point)")
            let coordinate = control.myMapView?.convert(point, toCoordinateFrom: control.myMapView)
            print("coordinate?.latitude is \(String(describing: coordinate?.latitude))")
            let annotation = MKPointAnnotation()
            annotation.coordinate = coordinate ?? sfCoord
            annotation.title = "Start"
            control.myMapView?.addAnnotation(annotation)
        }
    }
}//coord