NSTimer stops in Background while power cable is disconnected - iphone

Question

I have created GPS base Application.
In which App logged GPS data every 1 second.
App used the NSTimer to fetch GPS data every second.
This NSTimer is start in background. The NSTimer is start when app received the silent push notification from APNS.
I have seen a problem in iOS 7 that when Phone attached with power cable at that time timer call appropriately but without attached power cable timer stops while App in background.
Any inputs to resolve this issue greatly appreciated.

Answer 1

An NSTimer is not guaranteed to fire if your app is not in foreground. Once you unplug the cable the system puts your app into background to save battery.
Using an NSTimer is not the supported method to get location data. Your CLLocationManager will tell its delegate when there is a new location. No need to poll it.
If you need to track geolocation in background you need to declare location updates as a background mode from the capabilities tab in Xcode 5 target settings. Otherwise your location manager will stop delivering location updates once your app is not in foreground.

Answer 2

There are only few use cases that you can implement for foreground. If you don't want your application to be refused within review please don't use any hacks. Of course, you can use NSTimer in background, but it must be created in thread (runloop) of background task. But this background task lives for the only certain amount of time, so your timer must fire during this period. In other words, your first goal is to create background task, and only then you can use the timer. There are few cases suitable for your purpose (that allow you to create this task): 1.Monitor significant location changes or region 2.Fetch data (iOs 7). So please refer
-(void)application:(UIApplication *)application performFetchWithCompletionHandler:(void (^)(UIBackgroundFetchResult))completionHandler {
NSLog(#"BG fetch in action");
//the only 30 sec is allowed to perform all your actions
//during this period you can each second track GPS data
[self performSelector:#selector(finishBackgroundFetch:) withObject:completionHandler afterDelay:27];
[[NSNotificationCenter defaultCenter] postNotificationName:#"StartMyGPSRoutine" object:nil];
}
-(void)finishBackgroundFetch:(void (^)(UIBackgroundFetchResult))completionHandler {
NSLog(#"BG fetch completion handler");
[[NSNotificationCenter defaultCenter] postNotificationName:#"ForceStopAnyBackgroundTaskCreatedWithStartMyGPSRoutine" object:nil];
completionHandler(UIBackgroundFetchResultNewData);
}
of your application delegate -- this will be useful in your case as well as monitor significant location changes.
You ought to put anywhere:
if ([[UIApplication sharedApplication] respondsToSelector:#selector(setMinimumBackgroundFetchInterval:)]) {
NSLog(#"Set Force BG interval to %ld", interval);
[[UIApplication sharedApplication] setMinimumBackgroundFetchInterval:interval];
}
In my case I fetch the GPS data each 5 min so 27sec to complete this task is not so long. Anyway you can play with time intervals with XCode. Please refer Main Menu->Debug->Simulate Background Fetch