Properly launching an iOS app into the background from a location event - ios

Question

(iOS 11, Swift 4.1)
I wrote a cordova plugin in swift to handle region monitoring, but it isn't working properly when my app is suspended or killed. Here is my class with the relevant functions:
class GeofenceManager : NSObject, CLLocationManagerDelegate {
func locationManager(_ manager: CLLocationManager, didDetermineState state: CLRegionState, for region: CLRegion) {
switch state {
case .inside:
log ("Did Enter Region: " + region.identifier)
self.postGeofenceTransition(region: region, transitionType: 1)
break
case .unknown:
log ("Unknown Transition for region: " + region.identifier)
// self.postGeofenceTransition(region: region, transitionType: 1)
break
default:
break
}
}
func locationManager(_ manager: CLLocationManager, didExitRegion region: CLRegion) {
log ("Did Exit Region: " + region.identifier)
self.postGeofenceTransition(region: region, transitionType: 2)
}
func locationManager(_ manager: CLLocationManager, didStartMonitoringFor region: CLRegion) {
log("Did start monitoring region: " + region.identifier)
self.locationManager.requestState(for: region)
}
}
(I do it this way to handle someone that's already in the region when we start monitoring)
I've also got "didChangeAuthorizationStatus" that fetches and sets all the geofences, that is working fine.
In my AppDelegate (objc) I'm attempting to start Location Services if the app is opened from a region event, with
if([launchOptions objectForKey:UIApplicationLaunchOptionsLocationKey]) {
_locationManager = [[CLLocationManager alloc] init];
[_locationManager setDelegate:self];
[_locationManager setDistanceFilter:kCLHeadingFilterNone];
//change the desired accuracy to kCLLocationAccuracyBest
[_locationManager setDesiredAccuracy:kCLLocationAccuracyBest];
//SOLUTION: set setPausesLocationUpdatesAutomatically to NO
[_locationManager setPausesLocationUpdatesAutomatically:NO];
[_locationManager startUpdatingLocation];
}
My question is, if my app is opened from an event, i.e. "didEnterRegion", I immediately start location services, but will I hit my "didEnterRegion" delegate again? And am I doing something wildly wrong here?
I think I'm missing some understanding of iOS application states, have dug into the docs but it hasn't clicked yet. Any insight is very appreciated.

Answer 1

My question is, if my app is opened from an event, i.e. "didEnterRegion", I immediately start location services, but will I hit my "didEnterRegion" delegate again?
If your app was suspended or terminated, and if it is awakened or launched just to receive didEnterRegion, it stays in the background. It is given time just to handle this one event and then it is suspended.
You cannot start location updates with startUpdatingLocation at that point. You are in the background! Even if you are authorized for background updates, you cannot start getting updates while you are in the background. And even if you could, your code would fail, because you never set allowsBackgroundLocationUpdates. And even if you could do that, you wouldn't get any events, because you have no implementation of didUpdateLocation.
The correct procedure is: do nothing. Just handle didEnterRegion and get out. If the user enters the region again, your didEnterRegion will be called again. Region monitoring just goes on forever until you stop it (and make sure you do stop it, or the user may be be forced to delete your app).
Addendum: How to respond to being launched from scratch in the background like this? You can detect the key in didFinishLaunchWithOptions and handle it there and return false, or you can ignore it and return true and receive didEnterRegion. But either way you must immediately create a location manager and appoint its delegate or you will get nothing, obviously. This is why you should always create the location manager and set its delegate in your app delegate or root view controller, something that always exists, and exists as early as possible in the life of the app, as soon as it launches.