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.
Related
Our app would like to access accelerometer data in background. A possible way to achieve is to use Core Motion for accelerometer readings -
with
CLLocationManager* locationManager;
CMMotionManager* motionManager;
...
[motionManager startAccelerometerUpdatesToQueue: ... withHandler: ...]
which works fine on the foreground, but the only way I've found to receive the updates in background is to set the app to allow using Location in background, and call
[locationManager startUpdatingLocation]
in -applicationWillResignActive:
The problem is, when I call startUpdatingLocation that a window pops up with text Turn On Location Services to Allow "app" to Determine Your Location.
But of course, I receive accelerometer readings regardless of whether Location Services are enabled, but the popup is annoying and will probably confuse users.
Is getting accelerometer data in the background somewhat tied to attempting to receive location updates?
You can use startAccelerometerUpdatesToQueue in background, the only thing you need to meet — use any background mode to make you app running in the background (location updates (your case), playback, VoIP or BT4 central).
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'm trying using locationManager to get my location and update it to my webservice.
- (void)locationManager:(CLLocationManager *)manager
didUpdateToLocation:(CLLocation *)newLocation
fromLocation:(CLLocation *)oldLocation {
//some code here
}
It's normal, but if my app goes to the background or phone screen is locked, updating location may be paused. How do I get the location anyway?
Read the full blog post on it: iPhone Background GPS: accurate to 500m, not enough for foot traffic
Here is a tutorial: iOS Multitasking: Background Location
I recommend you set up a handler such as this example:
TTLocationHandler
Configure the handler for the recency and accuracy required. Set up a listener for the notification "LocationHandlerDidUpdateLocation". Put your code to upload the data in a method called on receipt of that notification.
If you do not require fine grain detail, I would advise you use the battery saving options of significantLocationChange monitoring in background. In that case you will not need to add background mode in info.plist and you will not waste resources unnecessarily. The app will be awakened and your method called only on significant movement of the user. There is configurable options in the handler to require constant monitoring in background and/or foreground, and to set recency and accuracy thresholds.
See the LMPinTracker class for example of how to respond and save your data to web or locally. See the thread Invoke get current coordinates every few seconds without NSTimer for discussion of use.
Add This Key to your Application Plist
Required background modes
Mark it as Array, and on its item0 add this Value
App registers for location updates
The app will now get location data in Background too.
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.
I understand that applicationWillTerminate is no longer called in iOS4, practically. But I have this situation:
my audiobook goes in background mode and keeps playing audio;
until version 3.x of SDK I saved the point where one listened to the MP3 file, in applicationWillTerminate;
now I was told to keep this saving in applicationWillTerminate (for iPhone 3G) and to implement the same method in applicationDidEnterBackground: but this saves NOT the point where user was at the end, just the point when he entered the background...
But, which is the moment, or better the invoked method, where user exits the application from the application dock? Does this exist?
ApplicationWillTerminate is called when there is a memory problem, but really I can't figure what happens when the user himself shuts down the app.
I repeat: applicationDidEnterBackground does not help me because when the user enters in background mode, he can stays in this position for a long time listening to the audiobook and when he starts again the app, after this is shut down, I mean, he will find the position of the audio file when he entered the background mode…
I'm really confused…
Thanks for your help!
You should save the play location automatically in applicationWillResignActive:, applicationDidEnterBackground: regardless of whether the audio keeps playing or not. Then put another save in applicationWillTerminate. That way the last play location is saved regardless of what happens next. The next event simply overwrites the saved play location to update it.
An even better option would be to have the audio player object itself trigger the save whenever it is interrupted e.g [AVAudioPlayerDelegate audioPlayerBeginInterruption:] or similar. It might takes some extra work but it would guarantee that the play location was always saved regardless of the cause of the interruption.