How do I get a background location update every n

Question

I'm looking for a way to get a background location update every n minutes in my iOS application. I'm using iOS 4.3 and the solution should work for non-jailbroken iPhones.

I tried / considered following options:

• CLLocationManager startUpdatingLocation/startMonitoringSignificantLocationChanges: This works in the background as expected, based on the configured properties, but it seems not possible to force it to update the location every n minutes
• NSTimer: Does work when the app is running in the foreground but doesn't seem to be designed for background tasks
• Local notifications: Local notifications can be scheduled every n minutes, but it's not possible to execute some code to get the current location (without the user having to launch the app via the notification). This approach also doesn't seem to be a clean approach as this is not what notifications should be used for.
• UIApplication:beginBackgroundTaskWithExpirationHandler: As far as I understand, this should be used to finish some work in the background (also limited in time) when an app is moved to the background rather than implementing "long-running" background processes.

How can I implement these regular background location updates?

Answer 1

I did write an app using Location services, app must send location every 10s. And it worked very well.

Just use the "allowDeferredLocationUpdatesUntilTraveled:timeout" method, following Apple's doc.

What I did are:

Required: Register background mode for update Location.

1. Create LocationManger and startUpdatingLocation, with accuracy and filteredDistance as whatever you want:

-(void) initLocationManager    
{
    // Create the manager object
    self.locationManager = [[[CLLocationManager alloc] init] autorelease];
    _locationManager.delegate = self;
    // This is the most important property to set for the manager. It ultimately determines how the manager will
    // attempt to acquire location and thus, the amount of power that will be consumed.
    _locationManager.desiredAccuracy = 45;
    _locationManager.distanceFilter = 100;
    // Once configured, the location manager must be "started".
    [_locationManager startUpdatingLocation];
}

2. To keep app run forever using allowDeferredLocationUpdatesUntilTraveled:timeout method in background, you must restart updatingLocation with new parameter when app moves to background, like this:

- (void)applicationWillResignActive:(UIApplication *)application {
     _isBackgroundMode = YES;

    [_locationManager stopUpdatingLocation];
    [_locationManager setDesiredAccuracy:kCLLocationAccuracyBest];
    [_locationManager setDistanceFilter:kCLDistanceFilterNone];
    _locationManager.pausesLocationUpdatesAutomatically = NO;
    _locationManager.activityType = CLActivityTypeAutomotiveNavigation;
    [_locationManager startUpdatingLocation];
 }

3. App gets updatedLocations as normal with locationManager:didUpdateLocations: callback:

-(void) locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations
{
//  store data
    CLLocation *newLocation = [locations lastObject];
    self.userLocation = newLocation;

   //tell the centralManager that you want to deferred this updatedLocation
    if (_isBackgroundMode && !_deferringUpdates)
    {
        _deferringUpdates = YES;
        [self.locationManager allowDeferredLocationUpdatesUntilTraveled:CLLocationDistanceMax timeout:10];
    }
}

4. But you should handle the data in then locationManager:didFinishDeferredUpdatesWithError: callback for your purpose

- (void) locationManager:(CLLocationManager *)manager didFinishDeferredUpdatesWithError:(NSError *)error {

     _deferringUpdates = NO;

     //do something 
}

5. NOTE: I think we should reset parameters of LocationManager each time app switches between background/forground mode.

Answer 2

Now that iOS6 is out the best way to have a forever running location services is...

- (void)applicationWillResignActive:(UIApplication *)application
{
/*
 Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
 Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.
 */

NSLog(@"to background");

app.isInBackground = TRUE;

UIApplication *app = [UIApplication sharedApplication];

// Request permission to run in the background. Provide an
// expiration handler in case the task runs long.
NSAssert(bgTask == UIBackgroundTaskInvalid, nil);

bgTask = [app beginBackgroundTaskWithExpirationHandler:^{
    // Synchronize the cleanup call on the main thread in case
    // the task actually finishes at around the same time.
    dispatch_async(dispatch_get_main_queue(), ^{

        if (bgTask != UIBackgroundTaskInvalid)
        {
            [app endBackgroundTask:bgTask];
            bgTask = UIBackgroundTaskInvalid;
        }
    });
}];

// Start the long-running task and return immediately.
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

    // Do the work associated with the task.

    locationManager.distanceFilter = 100;
    locationManager.desiredAccuracy = kCLLocationAccuracyHundredMeters;
    [locationManager startMonitoringSignificantLocationChanges];
    [locationManager startUpdatingLocation];

    NSLog(@"App staus: applicationDidEnterBackground");
    // Synchronize the cleanup call on the main thread in case
    // the expiration handler is fired at the same time.
    dispatch_async(dispatch_get_main_queue(), ^{
        if (bgTask != UIBackgroundTaskInvalid)
        {
            [app endBackgroundTask:bgTask];
            bgTask = UIBackgroundTaskInvalid;
        }
    });
});

NSLog(@"backgroundTimeRemaining: %.0f", [[UIApplication sharedApplication] backgroundTimeRemaining]);

}

Just tested it like that:

I started the app, go background and move in the car by some minutes. Then I go home for 1 hour and start moving again (without opening again the app). Locations started again. Then stopped for two hours and started again. Everything ok again...

DO NOT FORGET USING the new location services in iOS6

- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations
{   
    CLLocation *loc = [locations lastObject];

    // Lat/Lon
    float latitudeMe = loc.coordinate.latitude;
    float longitudeMe = loc.coordinate.longitude;
}

Answer 3

It seems that stopUpdatingLocation is what triggers the background watchdog timer, so I replaced it in didUpdateLocation with:

     [self.locationManager setDesiredAccuracy:kCLLocationAccuracyThreeKilometers];
     [self.locationManager setDistanceFilter:99999];

which appears to effectively power down the GPS. The selector for the background NSTimer then becomes:

- (void) changeAccuracy {
[self.locationManager setDesiredAccuracy:kCLLocationAccuracyBest];
[self.locationManager setDistanceFilter:kCLDistanceFilterNone];
}

All I'm doing is periodically toggling the accuracy to get a high-accuracy coordinate every few minutes and because the locationManager hasn't been stopped, backgroundTimeRemaining stays at its maximum value. This reduced battery consumption from ~10% per hour (with constant kCLLocationAccuracyBest in the background) to ~2% per hour on my device

Answer 4

To someone else having nightmare figure out this one. I have a simple solution.

1. look this example from raywenderlich.com-> have sample code, this works perfectly, but unfortunately no timer during background location. this will run indefinitely.

2. Add timer by using :

   -(void)applicationDidEnterBackground {
   [self.locationManager stopUpdatingLocation];
   
   UIApplication*    app = [UIApplication sharedApplication];
   
   bgTask = [app beginBackgroundTaskWithExpirationHandler:^{
       [app endBackgroundTask:bgTask];
       bgTask = UIBackgroundTaskInvalid;
   }];
   
    self.timer = [NSTimer scheduledTimerWithTimeInterval:intervalBackgroundUpdate
                                                 target:self.locationManager
                                               selector:@selector(startUpdatingLocation)
                                               userInfo:nil
                                                repeats:YES];
   
   }
   

3. Just don't forget to add "App registers for location updates" in info.plist.

Answer 5

Working Code(Entire Stepwise Code)

Step 1

• Go to project -> Capabilities -> Background Modes -> select Location updates.
• Go to Project -> Info -> add a key NSLocationAlwaysUsageDescription with an optional string.

Step 2

Add this code to AppDelegate.m

@interface AppDelegate ()<CLLocationManagerDelegate>
@property (strong, nonatomic) CLLocationManager *locationManager;
@property (strong, nonatomic) NSTimer *timer;
@end

Step 3 Add This Code in to applicationDidEnterBackground method in AppDelegate.m

    - (void)applicationDidEnterBackground:(UIApplication *)application {
        UIApplication *app = [UIApplication sharedApplication];
        __block UIBackgroundTaskIdentifier bgTaskId =
        [app beginBackgroundTaskWithExpirationHandler:^{
            [app endBackgroundTask:bgTaskId];
            bgTaskId = UIBackgroundTaskInvalid;
        }];

        dispatch_async( dispatch_get_main_queue(), ^{
            self.timer = nil;
            [self initTimer];
            [app endBackgroundTask:bgTaskId];
            bgTaskId = UIBackgroundTaskInvalid;
        });
    }

- (void)initTimer {
    if (nil == self.locationManager)
        self.locationManager = [[CLLocationManager alloc] init];

    self.locationManager.delegate = self;
    [self.locationManager requestAlwaysAuthorization];
    [self.locationManager startMonitoringSignificantLocationChanges];
    if (self.timer == nil) {
        self.timer = [NSTimer scheduledTimerWithTimeInterval:0.3
                                                      target:self
                                                    selector:@selector(checkUpdates:)
                                                    userInfo:nil
                                                     repeats:YES];
    }
}

- (void)checkUpdates:(NSTimer *)timer{
    UIApplication *app = [UIApplication sharedApplication];
    double remaining = app.backgroundTimeRemaining;
    if(remaining < 580.0) {
        [self.locationManager startUpdatingLocation];
        [self.locationManager stopUpdatingLocation];
        [self.locationManager startMonitoringSignificantLocationChanges];
    }
}

- (void)locationManager:(CLLocationManager *)manager
    didUpdateToLocation:(CLLocation *)newLocation
           fromLocation:(CLLocation *)oldLocation {
    NSLog(@"Did Update Location = %f / %f", [newLocation coordinate].latitude, [newLocation coordinate].longitude);
    [self updateLocationWithLatitude:[newLocation coordinate].latitude andLongitude:[newLocation coordinate].longitude];
    UIApplication*    app = [UIApplication sharedApplication];
    __block UIBackgroundTaskIdentifier bgTask =
    bgTask = [app beginBackgroundTaskWithExpirationHandler:^{
        [app endBackgroundTask:bgTask];
        bgTask = UIBackgroundTaskInvalid;
    }];
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        [self initTimer];
    });
}

- (void)locationManager:(CLLocationManager *)manager didFailWithError:(NSError *)error {
    [self.locationManager stopUpdatingLocation];
    UIApplication *app = [UIApplication sharedApplication];
    __block UIBackgroundTaskIdentifier bgTask =
    bgTask = [app beginBackgroundTaskWithExpirationHandler:^{
        [app endBackgroundTask:bgTask];
        bgTask = UIBackgroundTaskInvalid;
    }];
    [self initTimer];
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
        // Do the work associated with the task
    });
}

-(void)updateLocationWithLatitude:(CLLocationDegrees)latitude
                     andLongitude:(CLLocationDegrees)longitude{
//Here you can update your web service or back end with new latitude and longitude
}

Answer 6

In iOS 9 and watchOS 2.0 there's a new method on CLLocationManager that lets you request the current location: CLLocationManager:requestLocation(). This completes immediately and then returns the location to the CLLocationManager delegate.

You can use an NSTimer to request a location every minute with this method now and don't have to work with startUpdatingLocation and stopUpdatingLocation methods.

However if you want to capture locations based on a change of X meters from the last location, just set the distanceFilter property of CLLocationManger and to X call startUpdatingLocation().