I have an app which uses CLLocationManager to track the user's route, drawing dots along the path taken. The app runs in the background using Required background modes > App registers for location updates.
As I understand, anything that happens in the background needs to be called from locationManager:didUpdateToLocation:fromLocation as this is the method that gets called with each location update.
The problem I'm having is that sometimes this stops getting called. It seems to happen when the user's location does not change much within the space of maybe 15 minutes or so. As far as I can tell, calls to locationManager:didUpdateToLocation:fromLocation just stop, presumably to save the battery. Unfortunately, it doesn't resume again when you're back on the move.
I presume there's no way to override this behaviour, so I would like to use Notification Centre to inform the user that the app is no longer recording the route. The problem is, how can the app know that this has happened? If locationManager:didUpdateToLocation:fromLocation is not called, I can't fire my notification. If it is being called, the notification should not fire.
I don't think that there is any way to be notified that the location manager has stopped sending you events, but there is a way to prevent it from happening. In iOS 6, a new feature was added that allows the location manager to power down services if it doesn't think they are being used. If you do the following, the location manager will continue sending you events in the background until you run out of battery:
if ([self.locationManager respondsToSelector:#selector(pausesLocationUpdatesAutomatically)])
{
self.locationManager.pausesLocationUpdatesAutomatically = NO;
}
Also, in iOS6, you should be using locationManager:didUpdateLocations: as locationManager:didUpdateToLocation:fromLocation: is deprecated.
The 2 delegate methods:
-(void)locationManagerDidPauseLocationUpdates:(CLLocationManager *)manager
and
-(void)locationManagerDidResumeLocationUpdates:(CLLocationManager *)manager
tells you when the location updates stop and start due to pausing.
I have an app which uses CLLocationManager to track the user's route, drawing dots along the path taken. The app runs in the background using Required background modes > App registers for location updates.
As I understand, anything that happens in the background needs to be called from locationManager:didUpdateToLocation:fromLocation as this is the method that gets called with each location update.
The problem I'm having is that sometimes this stops getting called. It seems to happen when the user's location does not change much within the space of maybe 15 minutes or so. As far as I can tell, calls to locationManager:didUpdateToLocation:fromLocation just stop, presumably to save the battery. Unfortunately, it doesn't resume again when you're back on the move.
I presume there's no way to override this behaviour, so I would like to use Notification Centre to inform the user that the app is no longer recording the route. The problem is, how can the app know that this has happened? If locationManager:didUpdateToLocation:fromLocation is not called, I can't fire my notification. If it is being called, the notification should not fire.
Is there some kind of system notification that says location updates will cease?
I'm finding it quite hard to debug this as I can't take my Mac everywhere when I'm out and about testing the location on the device (there's only so much you can do in the simulator). Any tips for debugging would also be much appreciated!
If you haven't found the answer, I think it is because of a new attribute added to CLLocationManager called pausesLocationUpdatesAutomatically. The attribute defaults to YES, and its behaviour is exactly as you describe. Try setting it to NO and I think it will fix your problem.
Starting in iOS9, make sure you're also setting this property on your location manager:
[locationManager setAllowsBackgroundLocationUpdates:YES]
There's a delegate for location update did Fail
-(void)locationManager:(CLLocationManager *)manager didFailWithError:(NSError *)error
There are a few kinds of errors: kCLErrorDenied kCLErrorNetwork Add code here to handle them in the delegate method above not updating location, perhaps a UIAlertView to tell the user.
Personally, I call [locationManager stopUpdatingLocation]; on any error then restart it with an error message depending on the reason for the failure.
ALSO re background, check code in your appDelegate:
- (void)applicationDidEnterBackground:(UIApplication *)application
{
// Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.
// If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
[self saveContext];
if ([CLLocationManager significantLocationChangeMonitoringAvailable]) {
// Stop normal location updates and start significant location change updates for battery efficiency.
[self.locationHandler.locationManager stopUpdatingLocation];
[self.locationHandler.locationManager startMonitoringSignificantLocationChanges];
}
else {
NSLog(#"Significant location change monitoring is not available.");
}
}
LASTLY re: testing. You can simulate some errors in location by changing the location movement in the simulator. For example, going from running to driving will cause an error. Going from running to a single specific custom location will cause an error. They should all appear in the delegate method for locationManager above.
I've managed to solve the problem by adding a local notification that fires with a 90 second delay every time a new location is added to the route. When the next location is added, the previous notification is cancelled and a new one is scheduled. This way, if it stops updating, a notification is received by the user (albeit with a 90 second delay). It's not ideal, and it may not be great for battery life, but it is a solution and it's the best I've got for the time being.
#Ron, I meet the same problem as beev describe, and i had already set pausesLocationUpdatesAutomatically to NO. I think because iOS will kill some apps that didn't be triggered in 10 minutes when it's under background. So add local notification maybe a good choice at the moment.
I know how to set a timer and when timer expires, it fires and a action is caught.
What I'm expecting is that after 30 seconds of every one hour of real time that that "xx:00:30" I have to check my server for updates.
I know how to communicate with server. But how can I create such a timer that fires every "xx:00:30".
I don't want to run the timer if the app is in background.
Any ideas on how to do this?
As mentioned by Marcus in his last message,
NSTimer's initWithFireDate:interval:target:selector:userInfo:repeats: or setFireDate:
works.
I want to poll the location from GPS in the background. So we used a NSTimer and performed periodic checks in the timer tick. In other words, can we schedule NSTimer while the app is in Background?
Thanks in advance
You can't periodically execute arbitrary code, but you can get pinged on significant location changes via startMonitoringSignificantLocationChanges in CLLocationManager.
Is there a way to keep timers running when an App enters background mode without location services running?
If I have a timer running in the App with location services on and enter the background then it keeps running. However calling stopUpdatingLocation also stops the timer. I would like the timer to be able to call startUpdatingLocation at some point in the furture but as it not being run it can't do this.
Any information on how multi-tasking works with location services would be helpful.
You should probably figure out when (at what time) the timer would call startUpdatingLocation and add a UILocalNotification at that time.