ios - MKMapView userTrackingMode 在 SwiftUI 中重置

Question

我无法显示 MKMapView在 SwiftUI 中使用 userTrackingMode设置为 .follow .我正在展示一张 map :

struct ContentView: View {
    var body: some View {
        MapView()
    }
}

而在这个MapView我是 (a) 设置 userTrackingMode (b) 确保我拥有使用时权限。我一直在基于 Storyboard的项目中使用这种模式。无论如何，MapView现在看起来像:

final class MapView: UIViewRepresentable {
    private lazy var locationManager = CLLocationManager()

    func makeUIView(context: Context) -> MKMapView {
        if CLLocationManager.authorizationStatus() == .notDetermined {
            locationManager.requestWhenInUseAuthorization()
        }

        let mapView = MKMapView()
        mapView.showsUserLocation = true
        mapView.userTrackingMode = .follow  // no better is mapView.setUserTrackingMode(.follow, animated: true)
        return mapView
    }

    func updateUIView(_ uiView: UIViewType, context: Context) {
        print(#function, uiView.userTrackingMode)
    }
}

这里一切看起来都不错，但 map (在模拟器和物理设备上)实际上并未处于跟随用户跟踪模式。

所以，我在上面进行了扩展，添加了一个采用 MKMapViewDelegate 的协调器。协议(protocol)，所以我可以看到跟踪模式发生了什么:

final class MapView: UIViewRepresentable {
    private lazy var locationManager = CLLocationManager()

    func makeUIView(context: Context) -> MKMapView {
        if CLLocationManager.authorizationStatus() == .notDetermined {
            locationManager.requestWhenInUseAuthorization()
        }

        let mapView = MKMapView()
        mapView.delegate = context.coordinator
        mapView.showsUserLocation = true
        mapView.userTrackingMode = .follow  // no better is mapView.setUserTrackingMode(.follow, animated: true)
        return mapView
    }

    func updateUIView(_ uiView: UIViewType, context: Context) {
        print(#function, uiView.userTrackingMode)
    }

    func makeCoordinator() -> MapViewCoordinator {
        return MapViewCoordinator(self)
    }
}

class MapViewCoordinator: NSObject {
    var mapViewController: MapView

    var token: NSObjectProtocol?

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

extension MapViewCoordinator: MKMapViewDelegate {
    func mapView(_ mapView: MKMapView, didChange mode: MKUserTrackingMode, animated: Bool) {
        print(#function, mode)
    }
}

这导致:

mapView(_:didChange:animated:) MKUserTrackingMode.follow
updateUIView(_:context:) MKUserTrackingMode.follow
mapView(_:didChange:animated:) MKUserTrackingMode.none

There’s something going on that is resetting the userTrackingMode to .none.

For giggles and grins, I tried resetting userTrackingMode, and that is no better:

func updateUIView(_ uiView: UIViewType, context: Context) {
    print(#function, uiView.userTrackingMode)
    uiView.userTrackingMode = .follow
}

不过，这种笨拙的模式确实有效:

func updateUIView(_ uiView: UIViewType, context: Context) {
    print(#function, uiView.userTrackingMode)
    DispatchQueue.main.async {
        uiView.userTrackingMode = .follow
    }
}

或任何重置 userTrackingMode后来，经过这个初始过程，似乎也可以工作了。

我在 UIViewRepresentable 上做错了吗？ ? MKMapView 中的一个错误?

这并不相关，但这是我显示跟踪模式的例程:

extension MKUserTrackingMode: CustomStringConvertible {
    public var description: String {
        switch self {
        case .none:              return "MKUserTrackingMode.none"
        case .follow:            return "MKUserTrackingMode.follow"
        case .followWithHeading: return "MKUserTrackingMode.followWithHeading"
        @unknown default:        return "MKUserTrackingMode unknown/default"
        }
    }
}

Answer 1

令人愤怒的是，在花费大量时间调试、准备问题等之后，看起来这种奇怪的行为只有在你不提供 frame 时才会出现。初始化期间:

let mapView = MKMapView()

当我使用以下内容时(即使最终 map 不是这个大小)，它也可以正常工作:

let mapView = MKMapView(frame: UIScreen.main.bounds)

我仍然会发布这个，希望它能把其他人从这场噩梦中拯救出来。