How to get current coordinate span in swiftUI?

Question

I'm working with a map kit map and I need to get the current value of the coordinate span model. So that when you click on the map point, the map itself does not jump.

import SwiftUI
import MapKit

struct MapScreenView: View {

    @StateObject private var vm = LocationsViewModel()

    var body: some View {

        ZStack {
            VStack {
                HStack {
                    ButtonFilterView()
                    Spacer()
                }
                Spacer()
            }.zIndex(1)
            Map(coordinateRegion:
                    $vm.mapRegion, annotationItems: vm.locations) {
                location in
                MapAnnotation(coordinate: location.coordinate) {
                    LocationMapAnnotationView()
                        .scaleEffect(vm.mapLocation == location ? 1.1 : 0.7)
                        .animation(.easeInOut, value: vm.mapLocation == location)
                        .onTapGesture {
                            vm.showTappedLocation(location: location)
                        }
                }
            }
            .edgesIgnoringSafeArea(.all)
        }
    }
}

struct MapScreenView_Previews: PreviewProvider {
    static var previews: some View {
        MapScreenView()
    }
}

import Foundation
import MapKit
import SwiftUI

class LocationsViewModel: ObservableObject {

    @Published var locations: [Location] = LocationDataService.locations
    
    @Published var mapLocation: Location {
        didSet {
            updateMapRegion(location: mapLocation)
        }
    }

    @Published var mapRegion = MKCoordinateRegion()
    @Published var mapSpan = MKCoordinateSpan(latitudeDelta: 0.04, longitudeDelta: 0.04)
    
    init() {
        self.mapLocation = Location(name: "", coordinate: CLLocationCoordinate2D(latitude: 55.755864, longitude: 37.617698))
        updateMapRegion(location: Location(name: "", coordinate: CLLocationCoordinate2D(latitude: 55.755864, longitude: 37.617698)))
    }

    private func updateMapRegion(location: Location) {
        withAnimation(.easeInOut) {
            mapRegion = MKCoordinateRegion(
                center: location.coordinate,
                /// here i want get current span value
                span: location.name == "" ? MKCoordinateSpan(latitudeDelta: 0.1, longitudeDelta: 0.1) : mapSpan
            )
        }
    }

    func showTappedLocation(location: Location) {
            mapLocation = location
    }
}

When I click on the map pin, it returns to the hard code span. How can I get current span? I searched for many solutions, but did not find the right one

You created a whole new account just to ask the same question again?! LOL! Oh well, at least you put some code in this time. Let's take a look... — Fogmeister, Dec 21 '22 at 09:01
Thank you very much for your help. I tried to edit an old question, but it got closed. Thanks for your decision — Василий Старцев, Dec 21 '22 at 09:18
No worries. This is definitely a better written question. Have fun on Stack Overflow. It takes a while to learn how to write a really awesome question. You can learn from here if you need some guidance... https://stackoverflow.com/help/how-to-ask — Fogmeister, Dec 21 '22 at 09:20

score 0 · Accepted Answer · answered Dec 21 '22 at 09:06

SwiftUI Map takes a binding to a MKCoordinateRegion.

In your code you have...

Map(coordinateRegion: $vm.mapRegion, ...

This is a twi way communication between the view model's region and the map view. When the map updates, this region updates. When you update the region, the map updates.

So the current values of your map are help inside that mapRegion.

Looking at the docs for MKCoordinateRegion https://developer.apple.com/documentation/mapkit/mkcoordinateregion/1452293-span

It has a property span which is an MKCoordinateSpan.

So in the view model... this is the current span of the map.

To update your function you could do something like...

private func updateMapRegion(location: Location) {
    withAnimation(.easeInOut) {
        mapRegion = MKCoordinateRegion(
            center: location.coordinate,
            /// here i want get current span value
            span: mapRegion.span
        )
    }
}

Having said that, you seem to be creating a whole new region here. I don't know if that's a good idea. You could just update the center of the existing region without creating a whole new one.

private func updateMapRegion(location: Location) {
    withAnimation(.easeInOut) {
        mapRegion.center = location.coordinate
    }
}

Can you help me in my next question about map camera? Please https://stackoverflow.com/questions/74874887/how-to-add-mkmapcamera-and-read-current-value — Василий Старцев, Dec 21 '22 at 12:09
@ВасилийСтарцев I saw it but I don't have enough experience with it to answer. I'll have a look later at it to see if I can help. — Fogmeister, Dec 21 '22 at 14:29

How to get current coordinate span in swiftUI?

1 Answers1