Swift中的watchValueForKeyPath崩溃的应用程序

Question

I'm very new to iOS development and trying to wrap my head around why my app is crashing with a message of SIGABRT. I am following along a tutorial ( link ) on how to implement Google Maps SDK and as far as I can tell I have the same code.

My code:

@IBOutlet weak var mapView: GMSMapView!

let locationManager = CLLocationManager()
var didFindMyLocation = false

override func viewDidLoad() {
    super.viewDidLoad()

    // Do any additional setup after loading the view.
    locationManager.requestWhenInUseAuthorization()
    locationManager.delegate = self

    mapView.addObserver(self, forKeyPath: "myLocation", options: NSKeyValueObservingOptions.New, context: nil)

    }

func locationManager(manager: CLLocationManager, didChangeAuthorizationStatus status: CLAuthorizationStatus) {
    if status == CLAuthorizationStatus.AuthorizedWhenInUse {
        mapView.myLocationEnabled = true
    }
}

private func observeValueForKeyPath(keyPath: String, ofObject object: AnyObject, change: [NSObject : AnyObject], context: UnsafeMutablePointer<Void>) {
    if !didFindMyLocation {
        let myLocation: CLLocation = change[NSKeyValueChangeNewKey] as! CLLocation
        mapView.camera = GMSCameraPosition.cameraWithTarget(myLocation.coordinate, zoom: 10)
        mapView.settings.myLocationButton = true

        didFindMyLocation = true
    }
}

The crash happens as I add the last function observeValueForKeyPath and I cannot figure out why. I get the following error message:

Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: ': An -observeValueForKeyPath:ofObject:change:context: message was received but not handled. Key path: myLocation

Can someone tell me what I'm doing wrong?

Answer 1

The problem is that you haven't declared observeValueForKeyPath(_:ofObject:change:context:) correctly. Your method expects the wrong argument types for keyPath , ofObject , and change .

The fact that you didn't declare your method override is a clue: if you had declared it with the correct types, the compiler would tell you that it also needs to be declared override . (It would also tell you that you cannot declare it private , because it's public in NSObject .)

The correct declaration looks like this:

override func observeValueForKeyPath(keyPath: String?, ofObject object: AnyObject?,
    change: [String : AnyObject]?, context: UnsafeMutablePointer<Void>)

If you just start to type the method name at class scope, Xcode will offer to autocomplete the correct declaration: