连续中心的用户与Mapkit

Question

下午好，

我在显示地图时遇到了麻烦，它只以用户为中心，并将在移动的用户上停留。我的错误是在我的视图文件中，我标记了//HERE。

我的错误是类型'()'不符合'视图'

1. 为什么这一行会给我一个错误?如果这行运行，我的假设是地图区域正在改变，但它仍然会返回符合的地图。查看文件如下所示。

2. 如果我运行它没有注释行，它不显示我的当前位置。我的模拟器设置设置为Features>位置比;苹果。甚至当我把地图放大时，地图上也没有任何标记。

   
   import SwiftUI
   import MapKit
   struct Location: Identifiable {
   let id = UUID()
   let name: String
   let content: String?
   let lat: Double
   let lon: Double
   var dangerLevel: CGFloat? = 10.0
   var coord: CLLocationCoordinate2D { CLLocationCoordinate2D(latitude: lat, longitude: lon) }
   }
   struct ContentView: View {
   @EnvironmentObject var locationManager: LocationManager
   @State private var userTrackingMode: MapUserTrackingMode = .follow
   @State var region = MKCoordinateRegion(center: CLLocationCoordinate2D(latitude: 40.7128, longitude: 74.0060), span: MKCoordinateSpan( latitudeDelta: 0.03, longitudeDelta: 0.03))
   var body: some View {
   var locationManager = LocationManager()
   region = MKCoordinateRegion(center: locationManager.location!.coordinate, span: MKCoordinateSpan( latitudeDelta: 0.03, longitudeDelta: 0.03)) // HERE!!!!
   
   VStack {
   Map(coordinateRegion: $region,
   interactionModes: .all,
   showsUserLocation: true)
   }
   }
   }
   struct ContentView_Previews: PreviewProvider {
   static var previews: some View {
   ContentView().environmentObject(LocationManager())
   }
   }
   
   

这是我定义locationManager的下一个文件

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

override init() {
super.init()
self.locationManager.delegate = self
self.locationManager.desiredAccuracy = kCLLocationAccuracyBest
self.locationManager.requestWhenInUseAuthorization()
self.locationManager.startUpdatingLocation()
}
}
extension LocationManager : CLLocationManagerDelegate {
func locationManager(_ manager: CLLocationManager,
didUpdateLocations locations: [CLLocation]) {
guard let location = locations.last else { return }
self.location = location
}


}

Answer 1

您的代码有几个问题。首先，要回答这个问题，您应该避免将非视图的变量直接放入var body。虽然有办法绕过这一限制，但没有理由再这样做了。由于region不是视图，代码通过错误。是的，我知道你定义了var locationManagerViewBuilder把它当作变量的初始化，而不是变量本身。但是，您已经在头文件中定义了对locationManager的引用。使用。

我在你的代码中添加了一些注释，以帮助事情顺利进行。如果您还有问题，请告诉我。

struct ContentView: View {
// Unless you are using locationManager all over your code, you don't need to pass it as an
// .environmentObject, though you can if needed. Since this is the first instance in this example
// of locationManager, I made it a @StateObject.
@StateObject var locationManager = LocationManager()
@State private var userTrackingMode: MapUserTrackingMode = .follow
@State var region = MKCoordinateRegion(center: CLLocationCoordinate2D(latitude: 37.60697453, longitude: -122.42798519), span: MKCoordinateSpan( latitudeDelta: 0.03, longitudeDelta: 0.03))
var body: some View {
VStack {
Map(coordinateRegion: $region,
interactionModes: .all,
showsUserLocation: true)
// Since locationManager is an ObservableObject, you can watch for changes with .onChange(of:)
.onChange(of: locationManager.location) { newLocation in
// Never force unwrap an optional unless you just set it yourself in the code.
guard let newLocation = newLocation else { return }
region = MKCoordinateRegion(center: newLocation.coordinate, span: MKCoordinateSpan( latitudeDelta: 0.03, longitudeDelta: 0.03)) // HERE!!!!
}
}

}
}
import CoreLocation
// I would consider renaming this class. It can be confusing to see
// locationManager.locationManager in code.
class LocationManager: NSObject, ObservableObject {
private let locationManager = CLLocationManager()
@Published var location: CLLocation?
override init() {
super.init()
// You can generally drop .self, with some exceptions. The compiler will correct you.
locationManager.delegate = self
locationManager.desiredAccuracy = kCLLocationAccuracyBest
locationManager.requestWhenInUseAuthorization()
locationManager.startUpdatingLocation()
}
}
extension LocationManager : CLLocationManagerDelegate {
func locationManager(_ manager: CLLocationManager,
didUpdateLocations locations: [CLLocation]) {
guard let location = locations.last else { return }
// This is an exception to dropping self when a variable in a closure has the same name as a
// self variable.
self.location = location
}
}