iphone - NSTimers in background - objective-c

Question

Im developing an app that has to run in the background. It's a location based app, so it runs all the time, the OS doesn't kill it.
It should send some info every 10 secs(just for debugging), I set a timer once its in the background. I set a breakpoint in the function that should be executed every 10 secs, which is never called, but if I pause the app and then continue the timer is called, and then the timer is executed every 10 secs without problems, weird right?
I thought that the timer would be executing anyway when I wasn't debugging, but it isn't, same thing as if I didn't pause the debugging.
My question is WHY?? The timer is set correctly(I assume) since it works after pausing, but it's not.
Any ideas?
The way I set the timer is:
self.timer = [NSTimer scheduledTimerWithTimeInterval:10 target:self selector:#selector(doStuff) userInfo:nil repeats:YES];
And in the function I connect to a webservice.
Thanks.

Answer 1

I have a similar app design and was stuck on the same thing. What I found somewhere on the internet is adding this type of statement applicationDidEnterBackground:
UIBackgroundTaskIdentifier locationUpdater =[[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
[[UIApplication sharedApplication] endBackgroundTask:locationUpdater];
locationUpdater=UIBackgroundTaskInvalid;
} ];
This tells the os that you still have things going and not to stop it.
I have my timer attached to this function
//this is a wrapper method to fit the required selector signature
- (void)timeIntervalEnded:(NSTimer*)timer {
[self writeToLog:[NSString stringWithFormat:#"Timer Ended On %#",[NSDate date]]];
[self startReadingLocation];
[timer invalidate];
timer=nil;
}
I set the timer in my my location manager delegate methods.
I feel your pain. I found that these things were super finicky. This is what worked for me. I hope it helps. I have found that there isn't any really restrictions in what you can do in the background.

Answer 2

There might be restrictions on what you can do in the background. Try adding the timer to the run loop before going into the background. Even that might not work; it may be that the only code of yours that can run in the background is the code called by the Core Location methods you've signed up for (e.g. locationManager:didUpdate...). But my impression is that timers already running before you start to go into the background will continue to run.