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In the UIViewController, I have an NSTimer scheduled to fire every 1 second, using scheduledTimer method, so I could update a UILabel in the view every second. But the problem is, the NSTimer firing seemed to be delayed whenever I pan around the MKMapView that is inside also inside the UIView. So the delay results in the UILabel not updating uniformly, which is not good to see. Could the delay caused by MKMapView panning taking too much resources? How could I schedule the NSTimer so that there is no delay however I pan the MKMapView? (Note, however, that I didn't schedule the NSTimer on some kind of background thread, it is in the main thread.) Thanks.

Dharmesh Dhorajiya
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Blip
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  • Does setting up the timer in the background thread to do the calculation, then using `dispatch_async` code to get main thread to update the UI, work ? The dispatch_async example is shown in this asnwer: http://stackoverflow.com/questions/16283652/understanding-dispatch-async – Zhang Apr 04 '15 at 13:19
  • How are you scheduling the timer? You need to schedule it with `NSRunLoopCommonModes` if you want it to fire while scrolling/panning. – dan Apr 04 '15 at 14:00

1 Answers1

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If you use scheduledTimerWithTimeInterval(...) to create your timer, it will be added to the current runloop with mode NSDefaultRunLoopMode. The timer will not fire while your app is busy with event tracking, i.e. if you scroll around in a UIScrollView or if you do any other interactions with your UI.

You can create a unscheduled NSTimer and add it to the runloop yourself, if you use NSRunLoopCommonModes as mode the timer will fire while you interact with the user interface. 

let timer = NSTimer(timeInterval: 1.0, target: self, selector: Selector("timerFired:"), userInfo: nil, repeats: true)
NSRunLoop.currentRunLoop().addTimer(timer, forMode: NSRunLoopCommonModes)

For further information, the question NSDefaultRunLoopMode vs NSRunLoopCommonModes contains a nice explanation about the different runloop modes.

Community
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Matthias Bauch
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  • Thanks, but there is a problem...the app registers for background location updates, and the CLLocationManager I use to get location updates is defer-updates-enabled. I tried to add the timer to the run loop with NSRunLoopCommonModes, but it seems that the system kills the app when it runs for too long. I think it is because the NSTimer is taking up NSRunLoop when the run loop should be inactivated. – Blip Apr 04 '15 at 21:44
  • so invalidate the timer if the app goes into the background, and recreate it when the app comes into the foreground again – Matthias Bauch Apr 05 '15 at 10:45
  • Thank you, your genius suggestion solved my problem. – Blip Apr 07 '15 at 21:44