ios - 如果用户未批准位置信息，则每次打开 View 时如何请求访问位置信息的权限

Question

我试图打开一个需要访问用户位置的视图控制器。目前我正在运行下面的代码。但是，这只会在用户第一次打开视图时请求其权限。之后，如果用户拒绝，应用程序就会崩溃。
我在viewDidLoad（）的开头运行这个函数，然后运行

centerMapOnLocation(CLLocationManager().location!, mapView: mapView)

这一行代码将崩溃并显示错误消息：
线程1:致命错误：在展开可选值时意外找到nil
这是什么原因？

func askForPermission() {
    // Ask for Authorisation from the User.
    self.locationManager.requestAlwaysAuthorization()

    // For use in foreground
    self.locationManager.requestWhenInUseAuthorization()

    if CLLocationManager.locationServicesEnabled() == true {
        locationManager.delegate = self
        locationManager.desiredAccuracy = kCLLocationAccuracyNearestTenMeters
        locationManager.startUpdatingLocation()
    }
    else {
        let alertController = UIAlertController(title: "Location Service Error", message: "Go to settings to approve Location services", preferredStyle: .alert)

        // Create OK button
        let OKAction = UIAlertAction(title: "Ok", style: .default) { (action:UIAlertAction!) in
            UIApplication.shared.open(URL(string: UIApplication.openSettingsURLString)!)

        }
        alertController.addAction(OKAction)

        // Create Cancel button
        let cancelAction = UIAlertAction(title: "Cancel", style: .cancel) { (action:UIAlertAction!) in
            self.dismiss(animated: true, completion: nil)
        }
        alertController.addAction(cancelAction)

        // Present Dialog message
        self.present(alertController, animated: true, completion:nil)
    }
}

我还尝试运行以下函数，但在同一位置遇到崩溃。

func checkAuthorizationStatus() {
    switch CLLocationManager.authorizationStatus() {
    case .authorizedWhenInUse:
        mapView.showsUserLocation = true
        break
    case .denied:
        let alertController = UIAlertController(title: "Location Service Error", message: "Go to settings to approve Location services", preferredStyle: .alert)

        // Create OK button
        let OKAction = UIAlertAction(title: "Ok", style: .default) { (action:UIAlertAction!) in
            UIApplication.shared.open(URL(string: UIApplication.openSettingsURLString)!)

        }
        alertController.addAction(OKAction)

        // Create Cancel button
        let cancelAction = UIAlertAction(title: "Cancel", style: .cancel) { (action:UIAlertAction!) in
            self.dismiss(animated: true, completion: nil)
        }
        alertController.addAction(cancelAction)

        // Present Dialog message
        self.present(alertController, animated: true, completion:nil)
        break
    case .notDetermined:
        locationManager.requestWhenInUseAuthorization()
        mapView.showsUserLocation = true
        break
    case .restricted:
        let alertController = UIAlertController(title: "Location Service Error", message: "Go to settings to approve Location services", preferredStyle: .alert)

        // Create OK button
        let OKAction = UIAlertAction(title: "Ok", style: .default) { (action:UIAlertAction!) in
            UIApplication.shared.open(URL(string: UIApplication.openSettingsURLString)!)

        }
        alertController.addAction(OKAction)

        // Create Cancel button
        let cancelAction = UIAlertAction(title: "Cancel", style: .cancel) { (action:UIAlertAction!) in
            self.dismiss(animated: true, completion: nil)
        }
        alertController.addAction(cancelAction)

        // Present Dialog message
        self.present(alertController, animated: true, completion:nil)
        break
    case .authorizedAlways: break
    }
}

我该怎么解决？

Answer 1

你可以通过给某个特定的功能分配任何特定的按钮动作或某个活动，
`onClick（视图c）{
//在这里触发你的代码
函数askForPermission（）{….}
}`
另一方面，一个经典的Try-catch语句将很好地防止应用程序崩溃，或者您可以为这个特定事件使用不同的线程。