iphone - NSTimers in background

问题:

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.

回答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.

回答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.