Carey Carey - 6 months ago 273
iOS Question

Run a Swift 2.0 app forever in background to update location to server

I have written the below code that has a timer that calls a callback function every minute. When the app goes to the background I have started another timer that calls the same callback method, but the background timer works for only three minutes.

I understand that Apple allows background tasks for only three minutes. My app is more like a tracking app that tracks the location of the user every minute even when the app is in background, so I need to implement this functionality.

I learned that

beginBackgroundTaskWithExpirationHandler
is to be used but I don't know whether my implementation is correct.

Note: I have Required background modes in plist toApp registers for location updates.

Any working code or links are much appreciated.

override func viewDidLoad() {
super.viewDidLoad()

timeInMinutes = 1 * 60

self.locationManager.requestAlwaysAuthorization()

self.locationManager.requestWhenInUseAuthorization()

if CLLocationManager.locationServicesEnabled() {
locationManager.delegate = self
locationManager.desiredAccuracy = kCLLocationAccuracyNearestTenMeters
locationManager.startUpdatingLocation()
}

var timer = NSTimer.scheduledTimerWithTimeInterval( timeInMinutes, target: self, selector: "updateLocation", userInfo: nil, repeats: true)
}

func locationManager(manager: CLLocationManager, didUpdateLocations locations: [CLLocation]){
let locValue:CLLocationCoordinate2D = manager.location!.coordinate

self.latitude = locValue.latitude
self.longitude = locValue.longitude

if UIApplication.sharedApplication().applicationState == .Active {

} else {
backgroundTaskIdentifier = UIApplication.sharedApplication().beginBackgroundTaskWithExpirationHandler({ () -> Void in
self.backgroundTimer.invalidate()
self.backgroundTimer = NSTimer.scheduledTimerWithTimeInterval( 60.0, target: self, selector: "updateLocation", userInfo: nil, repeats: true)
})
}
}

func updateLocation() {
txtlocationLabel.text = String(n)
self.n = self.n+1

var timeRemaining = UIApplication.sharedApplication().backgroundTimeRemaining

print(timeRemaining)

if timeRemaining > 60.0 {
self.GeoLogLocation(self.latitude,Longitude: self.longitude) {
results in
print("View Controller: \(results)")
self.CheckResult(String(results))
}
} else {
if timeRemaining == 0 {
UIApplication.sharedApplication().endBackgroundTask(backgroundTaskIdentifier)
}

backgroundTaskIdentifier2 = UIApplication.sharedApplication().beginBackgroundTaskWithExpirationHandler({ () -> Void in
self.backgroundTimer.invalidate()
self.backgroundTimer = NSTimer.scheduledTimerWithTimeInterval( 60.0, target: self, selector: "updateLocation", userInfo: nil, repeats: true)
})
}
}

Answer

Periodic location updates are a bit tricky in IOS.There's a good thread that discusses this, you can read more here

iOS will terminate your app after a few minutes, regardless if your timer is running or not. There is a way around this though, I had to do something similar when writing an ionic app so you can check out the code for this here, that link has a swift class that manages the periodic location updates in iOs.

In order to get periodic locations in the background, and not drain the battery of the device, you need to play with the accuracy of the location records, lower the accuracy of the location manager setting its desiredAccuracy to kCLLocationAccuracyThreeKilometers, then, every 60 seconds you need to change the accuracy to kCLLocationAccuracyBest, this will enable the delegate to get a new, accurate location update, then revert the accuracy back to low. The timer needs to be initialized every time an update is received.

There's also a way to wake up the app in the background after its been killed by the user, use the app delegate to have the app listen for significant changes in location before its killed. This will wake up the app in the background when the user's location makes a big jump (can be around 200ms). When the app wakes up, stop monitoring for significant changes and restart the location services as usual to continue the periodic updates.

Hope this helps.

Update

In Swift 2 you'll also need:

self.locationManager.allowsBackgroundLocationUpdates = true