Question

I am trying to implement the suggestions given in this post.

Unfortunately the steps are not clear to me. I tried implementing those suggestions, but the backgroundTimeRemaining continues to decrease even after I start and stop locationServices. This is how I developed it:

- (void)applicationDidEnterBackground:(UIApplication *)application {

    UIApplication*    app = [UIApplication sharedApplication];

    bgTask = [app beginBackgroundTaskWithExpirationHandler:^{
        [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.
        self.timer = nil;
        [self initTimer];

    });
}

initTimer:

- (void)initTimer {

    // Create the location manager if this object does not
    // already have one.
    if (nil == self.locationManager)
        self.locationManager = [[CLLocationManager alloc] init];

    self.locationManager.delegate = self;
    [self.locationManager startMonitoringSignificantLocationChanges];

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

checkUpdates:

- (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];
    }
    DbgLog(@"Reminaing %f", app.backgroundTimeRemaining);
}

Does anyone have a suggestion on what might be wrong in my code? Both initTimer and checkUpdates are being called, but only during for the background execution time (+- 10 Mins). I want the app to update the location every n minutes “forever”.

My app’s UIBackgroundModes is set to location.

UPDATE:

I am now resetting the timer on didUpdateToLocation and didFailWithError. But still the backgroundTimeRemaining keeps decreasing:

- (void)locationManager:(CLLocationManager *)manager 
didUpdateToLocation:(CLLocation *)newLocation 
       fromLocation:(CLLocation *)oldLocation {

NSLog(@"Did Update Location = %f / %f", [newLocation coordinate].latitude, [newLocation coordinate].longitude);

UIApplication*    app = [UIApplication sharedApplication];

bgTask = [app beginBackgroundTaskWithExpirationHandler:^{
    [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.

    [self initTimer];

});
}

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

[self.locationManager stopUpdatingLocation]; 
UIApplication*    app = [UIApplication sharedApplication];

bgTask = [app beginBackgroundTaskWithExpirationHandler:^{
    [app endBackgroundTask:bgTask];
    bgTask = UIBackgroundTaskInvalid;
}];

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

    // Do the work associated with the task.

});

}

I am also invalidating the timer:

- (void)checkUpdates:(NSTimer *)timer{
UIApplication*    app = [UIApplication sharedApplication];
double remaining = app.backgroundTimeRemaining;
if(remaining < 580.0 && remaining > 570.0) {
    [self.timer invalidate];
    self.timer = nil;
    [self.locationManager startUpdatingLocation]; 
    [self.locationManager stopUpdatingLocation]; 
}
DbgLog(@"*************************Checking for updates!!!!!!!!!!! Reminaing %f", app.backgroundTimeRemaining);
}

Answer 1

After some days trying all possible solutions I was finally able to make it work. Here is what was wrong in my solution:

• I need to setup 2 UIBackgroundTaskIdentifiers, one for the timer, and another one for the locationManager

On my solution, just add:

UIApplication *app = [UIApplication sharedApplication];

bgTask2 = [app beginBackgroundTaskWithExpirationHandler:^{ 
[app endBackgroundTask:bgTask2]; 
bgTask2 = UIBackgroundTaskInvalid; }];

self.locationManager.delegate = self; 
[self.locationManager startUpdatingLocation];