应用程序在GMSMAPVIEW上运行多次时崩溃

Question

我有一个应用程序，它可以在用户位置附近找到位置，但是，该应用程序在第二次运行时崩溃，出现异常：致命错误：在展开可选值时意外发现nil。在线：self.googleMapView.animate(到位置：坐标(

我检查了一下，谷歌地图视图为零，但我不明白它是如何为零的，也不明白它第一次是如何运行的。如果我删除并重新安装应用程序，它只会在随后的尝试中开始崩溃，第一次尝试时效果良好，但之后即使我重新启动应用程序，也会不断崩溃。以下的完整代码

import UIKit
import GoogleMaps
import GooglePlacePicker
import MapKit
class MapViewController: UIViewController, CLLocationManagerDelegate {
var currentLongitude: CLLocationDegrees = 0
var currentLatitude: CLLocationDegrees = 0
var locationManager: CLLocationManager!
var placePicker: GMSPlacePickerViewController!
var googleMapView: GMSMapView!
@IBOutlet weak var mapViewContainer: MKMapView!
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
self.googleMapView = GMSMapView(frame: self.mapViewContainer.frame)
self.googleMapView.animate(toZoom: 18.0)
self.view.addSubview(googleMapView)
}
override func viewDidLoad() {
super.viewDidLoad()
self.locationManager = CLLocationManager()
self.locationManager.delegate = self
self.locationManager.requestAlwaysAuthorization()
self.locationManager.requestWhenInUseAuthorization()
self.locationManager.startUpdatingLocation()
}
func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
if let location:CLLocation = locations.last {
self.currentLatitude = location.coordinate.latitude
self.currentLongitude = location.coordinate.longitude
}
else {
print("Location Error")
}
let coordinates = CLLocationCoordinate2DMake(self.currentLatitude, self.currentLongitude)
let marker = GMSMarker(position: coordinates)
marker.title = "I am here"
marker.map = self.googleMapView
self.googleMapView.animate(toLocation: coordinates)
}

private func locationManager(manager: CLLocationManager,
didFailWithError error: Error){
print("An error occurred while tracking location changes : (error.localizedDescription)")
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}

}

Answer 1

崩溃是不言自明的：

您在viewDidLoad中设置位置的代理，但在viewDidAppear中创建地图。

如果iOS知道位置，您将在viewDidAppear呼叫之前收到消息，因此在线路中：self.googleMapView.animate(toLocation: coordinates)，您的地图仍然是nil

您可以将地图定义为可选：var googleMapView: GMSMapView?，也可以等待地图被定义以创建位置管理器。