尝试绑定它们时，从 CLLocationManager 初始化程序/自我错误创建 MapCameraPosition

Question

尝试使用新的 Swift @Observable 来监控 SwiftUI 内容视图中的 GPS 位置。但如何将最新位置与 SwiftUI 地图的 mapCameraPosition 关联起来？

理想情况下答案可以涵盖：

1. 如何修复此错误 - 因此获取地图跟踪以及用户位置，而且
2. 如何包含打开/关闭地图移动以跟踪用户位置的功能（接下来我需要这样做）。因此可以进行跟踪，然后禁用，移动地图并查看一些内容，然后单击按钮开始再次将地图相机位置同步到 GPS 位置

请参阅我嵌入在下面的代码中的错误。

import SwiftUI
import MapKit

@Observable
final class NewLocationManager : NSObject, CLLocationManagerDelegate {
    var location: CLLocation? = nil
    private let locationManager = CLLocationManager()

    func startCurrentLocationUpdates() async throws {
        if locationManager.authorizationStatus == .notDetermined {
            locationManager.requestWhenInUseAuthorization()
        }
        for try await locationUpdate in CLLocationUpdate.liveUpdates() {
            guard let location = locationUpdate.location else { return }
            self.location = location
        }
    }
   
}

struct ContentView: View {
    var newlocationManager = NewLocationManager()
    
    @State private var cameraPosition: MapCameraPosition = .region(MKCoordinateRegion(
        center: newlocationManager.location?.coordinate ?? <#default value#>,
        span: MKCoordinateSpan(latitudeDelta: 0.25, longitudeDelta: 0.25)
    ))
    // GET ERROR: Cannot use instance member 'newlocationManager' within property initializer; property initializers run before 'self' is available

    var body: some View {
        ZStack {
            Map(position: $cameraPosition)
            Text("New location manager: \(newlocationManager.location?.description ?? "NIL" )") // works
        }
        .task {
            try? await newlocationManager.startCurrentLocationUpdates()
        }
        
    }
}

#Preview {
    ContentView()
}

Answer 1

正如错误所述，您无法使用

newlocationManager

在视图初始化完成之前。

尝试使用

.onAppear{...}

，如示例代码所示。

struct ContentView: View {
    @State var newlocationManager = NewLocationManager() // <--- here
    
    @State private var cameraPosition: MapCameraPosition = .region(MKCoordinateRegion(
        center: CLLocationCoordinate2D(latitude: 35.68, longitude: 139.75), // <--- here, adjust
        span: MKCoordinateSpan(latitudeDelta: 0.25, longitudeDelta: 0.25)
    ))
    
    var body: some View {
        ZStack {
            Map(position: $cameraPosition)
            Text("New location manager: \(newlocationManager.location?.description ?? "NIL" )") // works
        }
        .task {
            try? await newlocationManager.startCurrentLocationUpdates()
        }
        .onAppear { // <--- here
            cameraPosition = .region(MKCoordinateRegion(
                center: newlocationManager.location?.coordinate 
                ?? CLLocationCoordinate2D(latitude: 35.68, longitude: 139.75),
                span: MKCoordinateSpan(latitudeDelta: 0.25, longitudeDelta: 0.25)
            ))
        }
        
    }
}