展开 CLLocation 位置坐标时出现致命错误

Question

I currently have a test application to teach myself Core Location. It is an app with a button which will either show your location when you press a button, or an alert when location services are off.

I get a fatal error (unexpectedly found nil when unwrapping option value) When location services are on and I attempt to println the string. I cannot find anywhere in the documentation where the CLLocationManager.location.coordinate returns an optional value. I will include the code snippet. Thanks!

let locationManager = CLLocationManager()

override func viewDidLoad() {
    super.viewDidLoad()
    if CLLocationManager.authorizationStatus() == .NotDetermined {
    locationManager.requestWhenInUseAuthorization()
    }
}

@IBAction func testLocation(sender: AnyObject) {
    switch CLLocationManager.authorizationStatus() {
    case .AuthorizedAlways, .AuthorizedWhenInUse:
        printCurrentCoordinates()
    case .Restricted, .Denied:
        disabledLocationSeriveAlert()
    default:
        println("Failed")
    }
func printCurrentCoordinates() {
    locationManager.desiredAccuracy = kCLLocationAccuracyBest
    locationManager.startUpdatingLocation()
    println("\(locationManager.location.coordinate.latitude)")
    println("\(locationManager.location.coordinate.longitude)")
}

func disabledLocationSeriveAlert() {
    let alert = UIAlertController(title: "Unable to retrieve location", message: "Enable location services in system settings", preferredStyle: UIAlertControllerStyle.Alert)
    alert.addAction(UIAlertAction(title: "Dismiss", style: UIAlertActionStyle.Default, handler: nil))
    self.presentViewController(alert, animated: true, completion: nil)
}

Answer 1

It looks like you aren't giving the CLLocationManager enough time to update the location.

---

I looked at the documentation, and in the statement locationManager.location.coordinate.latitude , location is the only one that's an optional. It's implicitly unwrapped, so that's why you don't need an ! after it.

In the printCurrentCoordinates method, you attempt to print the coordinates immediately after you call startUpdatingLocation . The documentation for location says:

The value of this property is nil if no location data has ever been retrieved.

And the documentation for startUpdatingLocation says:

This method returns immediately. Calling this method causes the location manager to obtain an initial location fix (which may take several seconds) and notify your delegate by calling its locationManager:didUpdateLocations: method.

So, you aren't giving the location manager enough time to get a location fix before you attempt to print the location.

You have a couple of choices - you can call startUpdatingLocation earlier and then print the coordinates in printCurrentCoordinates , or you could have printCurrentCoordinates start updating the location and then print the coordinates in locationManager:didUpdateLocations: .

Answer 2

The issue is location property of locationManager will be nil at that time.

That property contains the most recently retrieved location data. You just allocated location manager, at that time there won't be any data in that property.

According to CLLocationManager Class Reference :

location

Property The most recently retrieved user location. (read-only)

Declaration

@NSCopying var location: CLLocation! { get }

Discussion

The value of this property is nil if no location data has ever been retrieved.

Answer 3

location is nil when not set (from doc)

The value of this property is nil if no location data has ever been retrieved.

You have to use delegate to get the location. This is asynchronous operation, so value not available right after call startUpdatingLocation()

You must implement CLLocationManagerDelegate (and set your object as delegate) and wait for locationManager:didUpdateLocations: method - only then location will have some data.

Answer 4

Obtaining the location is an asynchronous operation - in fact the method you invoke to start the op is startUpdatingLocation() and not getLocation() . That is an indication that the process is started, and it's not completed at the time the invoked method returns.

The location is provided asynchronously via the func locationManager(manager: CLLocationManager!, didUpdateLocations locations: [AnyObject]!) method, part of the CLLocationManagerDelegate protocol that you must adopt in your class. And of course you have to set the delegate property of the CLLocationManager instance. If you have ever worked with tables, you should know how it works.

However, I recommend reading the official docs, or a good tutorial likethis one