ios - Update location in Background

Question

I want to get user location even when the user does not use the app.now i can get location after press home button and application goes to background state, but after a few second location update stoped. And when I'm killing the app location update against stoped. this is my code in app delegate.

 let locationManager = CLLocationManager()
  var LatitudeGPS = String()
  var LongitudeGPS = String()
  var speedGPS = String()
  var Course = String()
  var Altitude = String()
  var bgtimer = Timer()

func applicationDidEnterBackground(_ application: UIApplication) {

    self.doBackgroundTask()
  }

  func beginBackgroundUpdateTask() {

    backgroundUpdateTask = UIApplication.shared.beginBackgroundTask(expirationHandler: {
      self.endBackgroundUpdateTask()
    })

  }

  func endBackgroundUpdateTask() {
    UIApplication.shared.endBackgroundTask(self.backgroundUpdateTask)
    self.backgroundUpdateTask = UIBackgroundTaskInvalid
  }
func doBackgroundTask() {

  DispatchQueue.global(qos: .background).async {

    self.beginBackgroundUpdateTask()
    self.StartupdateLocation()
    self.bgtimer = Timer.scheduledTimer(timeInterval: 30, target: self, selector: #selector(self.bgtimer(timer:)), userInfo: nil, repeats: true)
    RunLoop.current.add(self.bgtimer, forMode: RunLoopMode.defaultRunLoopMode)
    RunLoop.current.run()
    self.endBackgroundUpdateTask()

  }


}


func bgtimer(timer:Timer!){
  print("Fired from Background ************************************")
  updateLocation()
}
  func StartupdateLocation() {
    locationManager.delegate = self
    locationManager.startUpdatingLocation()
    locationManager.desiredAccuracy = kCLLocationAccuracyBest
    locationManager.distanceFilter = kCLDistanceFilterNone
    locationManager.requestAlwaysAuthorization()
    locationManager.allowsBackgroundLocationUpdates = true
    locationManager.pausesLocationUpdatesAutomatically = false
  }

  func updateLocation() {
locationManager.startUpdatingLocation()
    locationManager.stopUpdatingLocation()
    print("Latitude: (LatitudeGPS)")
    print("Longitude: (LongitudeGPS)")
    print("Speed: (speedGPS)")
    print("Heading: (Course)")
    print("Altitude BG: (Altitude)")
    DispatchQueue.main.async {
      print(UIApplication.shared.backgroundTimeRemaining)

    }
  }

  func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {

    LatitudeGPS = String(format: "%.10f", manager.location!.coordinate.latitude)
    LongitudeGPS = String(format: "%.10f", manager.location!.coordinate.longitude)
    speedGPS = String(format: "%.3f", manager.location!.speed)
    Altitude = String(format: "%.3f", manager.location!.altitude)
    Course = String(format: "%.3f", manager.location!.course)

  }
}

i think after a few second my application terminated and location update stoped. I want to after 20 min that application terminated (os or user) stop updating location to keep the battery charge. where is my problem in location update.

Answer 1

Couple of things to be changed.

Step 1:

Make sure you have enabled location updates background mode in capabilities section of your project as shown below

Step 2:

And when I'm killing the app location update against stoped.

Quoting from apple docs

If you start this service and your app is subsequently terminated, the system automatically relaunches the app into the background if a new event arrives. In such a case, the options dictionary passed to the application(:willFinishLaunchingWithOptions:) and application(:didFinishLaunchingWithOptions:) methods of your app delegate contains the key location to indicate that your app was launched because of a location event. Upon relaunch, you must still configure a location manager object and call this method to continue receiving location events. When you restart location services, the current event is delivered to your delegate immediately. In addition, the location property of your location manager object is populated with the most recent location object even before you start location services.

link : https://developer.apple.com/documentation/corelocation/cllocationmanager/1423531-startmonitoringsignificantlocati

important thing to notice in above statement is

Upon relaunch, you must still, configure a location manager object and call this method to continue receiving location events.

Meaning, your current location manager will not be of much use and you should create a new one and configure the new instance and call startMonitorSignificantLocationChanges again.

So iOS will send location updates to terminated apps only when you use startMonitoringSignificantLocationChanges.

All that are applicable only if your app was terminated and iOS relaunched it on receiving location update. But if your app is simply in background you need not do any thing on using startMonitorSignificantLocationChanges

on the other hand startUpdatingLocation will work only when app is in background/foreground mode. iOS will stop updating location if your app gets suspended or killed.

If you start this service and your app is suspended, the system stops the delivery of events until your app starts running again (either in the foreground or background). If your app is terminated, the delivery of new location events stops altogether. Therefore, if your app needs to receive location events while in the background, it must include the UIBackgroundModes key (with the location value) in its Info.plist file.

link: https://developer.apple.com/documentation/corelocation/cllocationmanager/1423750-startupdatinglocation

So modify your code

 locationManager.startMonitoringSignificantLocationChange()

Ok that was about proper usage of startMonitoringSignificantLocationChanges and startupdatinglocation. Now timer for mistakes in your code.

Mistake 1:

self.bgtimer = Timer.scheduledTimer(timeInterval: 30, target: self, selector: #selector(self.bgtimer(timer:)), userInfo: nil, repeats: true)

Using timer to get timely updates on location. Thats not how it works!!! You cant run Timer forever. Timer stops as soon as your app suspends or gets terminated. Location Manager informs the app when location changes and you should rely on that only. You cant run timer to timely check location updates. It won't run in suspended or terminated state.

Mistake 2:

  func updateLocation() {
    locationManager.startUpdatingLocation()
    locationManager.stopUpdatingLocation()

Why start and stopping update locations in subsequent statements? That does not make much sense.

Mistake 3:

func StartupdateLocation() {
    locationManager.delegate = self
    locationManager.startUpdatingLocation()

Your StartupdateLocation gets called multiple time and every time you called this method you are repeatedly calling startUpdatingLocation on same instance of location manager. You need not do that! You can call startUpdatingLocation or startMonitoringSignificantLocationChange only once.