Question

I’ve an app which run in background, and I want to stop all location services 30 min after entering into background mode.

So in my background function, I do this :

// 1800 sec = 30 min * 60 sec.
NSDate *date30min = [[NSDate alloc] initWithTimeIntervalSinceNow:1800.0];
NSLog(@"Date30min : %@", date30min);

self.timer = [[NSTimer alloc] initWithFireDate:date30min interval:1 target:self selector:@selector(stopLocation) userInfo:nil repeats:NO];

And my stopLocation function is :

- (void)stopLocation
{
    NSLog(@"[My APP] [PASS INTO stopLocation]");
    [self.locationManager stopMonitoringSignificantLocationChanges];
    [self.locationManager stopUpdatingLocation];
    [self.locationManager stopUpdatingHeading];
}

But my timer never call the function, what’s my error please ?
(My function is correctly implement into my .h and .m file, I tested this out of the background function.

Please help..

Answer 1

It’s not a problem with forgetting to add your timer to a run loop (in this case).

NSTimer objects don’t fire when your app goes into the background. So, I would use another technique if you want to do something 30 minutes after backgrounding.

For example, use a Background Task to run your stopLocation method later:

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

    __block UIBackgroundTaskIdentifier bgTask = [application beginBackgroundTaskWithExpirationHandler: ^{
         NSLog(@" expiration handler!"); 
    }];

    dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 30 * 60 * NSEC_PER_SEC), dispatch_get_current_queue(), ^{

         [self stopLocation];

         // we're done with this task now
         [application endBackgroundTask: bgTask]; 
         bgTask = UIBackgroundTaskInvalid;
    });
}

Of course, you also need to have declared this:

<key>UIBackgroundModes</key>
<array>
    <string>location</string>
</array>

in your Info.plist file, but I assume you already figured that out.