set a timer in ios - ios

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.