CLLocationManager在后台时不更新，并获得混乱的位置坐标Swift

Question

I have a tracking function but it doesn't update location while in background.

1st case: Tracking while app is in the foreground -> the tracking is actually happening but doesn't get precise coordinates. I will change to locationManager.desiredAccuracy = kCLLocationAccuracyBestForNavigation to see if improves accuracy of the tracking.

2nd case: Tracking while screen is off -> the tracking is a straight line from a to b, tracking doesn't update coordinates.

3rd case: Tracking while app is in back ground(pressed home button) -> tracking is happening as case 1.

I found a post that explains that if authorisation is set to always you have to specify you want to keep updating location while in background, but nothing has changed. This is the code and info.plist :

override func viewDidLoad() {
        super.viewDidLoad()


        mapView.delegate = self
        locationManager.delegate = self
//        locationManager.desiredAccuracy = kCLLocationAccuracyBest
        locationManager.desiredAccuracy = kCLLocationAccuracyBestForNavigation
//        locationManager.allowsBackgroundLocationUpdates = true  //for getting user location in background mode as well

        mapView.showsUserLocation = true
        mapView.userTrackingMode = .follow   //map following user                    

        configureLocationServices()
        addDoubleTap() // enabling duble tap gesture recognizer
//        mapView.isUserInteractionEnabled = true

        let location = locationManager.location?.coordinate
        let region = MKCoordinateRegionMakeWithDistance(location!, 1000, 1000) // set mapView based on user location coordinates
        mapView.setRegion(region, animated: true)
        centerMapOnLocation()

        // alerts coordinates to post to Firebase
        let alertDrawLatitude =  alertDrawCoordinates?.latitude  // not used ?
        let alertDrawLomgitude = alertDrawCoordinates?.longitude
        let title: String? = alertNotificationType
        var subtitle: String? = alertNotificationType

        //  user alert notification. takes coordinates from alertNotificationArray( populated with firebase returning coordinate for all alerts

         displayAlerts()
    }            

    func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
        guard let mostRecentLocation = locations.last else { return }        
        self.actualRouteInUseCoordinatesArray.append(mostRecentLocation.coordinate)

    }            

    func configureLocationServices() {
            if authorizationStatus == .notDetermined{
                locationManager.requestAlwaysAuthorization()
            } else if authorizationStatus == .authorizedAlways {
            locationManager.showsBackgroundLocationIndicator = true //set update location even if in background. very imposrtant!!
          }
        }

UPDATE:

changing the accuracy only made things worse.

with AccuracyBest:

and with AccuracyBestForNAvigation

second tracking is actually worse.. how can navigation apps rely on this kind of tracking? is there anything wrong with my code for LocationManager?

SECOND UPDATE: it now get updated location when in background, but is way off..I never passed the yellow street and it shows like I waked for 10 minutes after it..

THIRD EDIT:

I found out that I should filter out GPS raw data, so I'm using a Kalman filter, and it really smooths out the resulting tracking. So I'm fine tuning two parameters, and in order to be able to change those parameters I added two textfields @IBOutlet weak var filterValueTextField: UITextField! and @IBOutlet weak var horizontalAccuracyTextField: UITextField! and connected those to the parameters

hcKalmanFilter?.rValue = Double(String( describing:filterValueTextField?.text!))! and guard mostRecentLocation.horizontalAccuracy < Double(String( describing: horizontalAccuracyTextField?.text!))! else { return } guard mostRecentLocation.horizontalAccuracy < Double(String( describing: horizontalAccuracyTextField?.text!))! else { return } . My problem is now that it finds nil while unwrapping value in the horizontalAccuracy parameter. If in horizontalAccuracy I just put a value it accepts an integer, but when I take it from the texField converting the textfield.text to Int, compiler throws an error Binary operator '<' cannot be applied to operands of type 'CLLocationAccuracy' (aka 'Double') and 'Int' , while if I convert it to Double doesn't, but it finds nil. Why the filterValue finds a value from it's textField, and the horizontal Accuracy doesn't? they're declared, and use the same way. Any idea?

Answer 1

First of all you have limited time while your app goes to background, and that time is depend upon load on your device's OS, but most probably it is approx. 30 seconds. So this is the reason your are not getting location updates while your screen is off or while your app goes to background.

But Apple allows app to run in background for some tasks and location update is one of them, so you can fetch location updates even if your app goes to background by enabling Background Fetch capability for your app.

For more details please follow below official doc. of Apple:

https://developer.apple.com/documentation/corelocation/getting_the_user_s_location/handling_location_events_in_the_background

And secondly try to maintain your locationmanager object in global scope of your app like you can place it in AppDelegate or in Singleton class if you are maintaining any for your app, so it will always be available.

Answer 2

Sometimes location that you receive does not have desired accuracy, especially when you've just started tracking, first couple of locations are going to be well off. You can use location's horizontal accuracy property to filter location witch have, for example, less then 50m accuracy