屏幕锁定时的NSTimer

Question

How do I keep the NSTimer persisting after the screen is locked in iOS 8? Every time I lock the screen it stops. I have tried putting it in an NSRunLoop to no luck.

Answer 1

iOS always suspends NSTimers when the app is backgrounded. You can request some extra background time by using UIApplication beginBackgroundTaskWithExpirationHandler: but be warned that it won't keep your timer going forever. Your best bet is to remember what time you are backgrounded in applicationWillResignActive and then check the current time when you are re-activated in applicationDidBecomeActive or applicationWillEnterForeground . Then you can calculate how much time passed when your app was inactive and do whatever is appropriate.

See the UIApplication docs here https://developer.apple.com/library/ios/documentation/uikit/reference/UIApplication_Class/Reference/Reference.html , particularly the section on "Managing Background Execution".