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    <p>You <a href="https://stackoverflow.com/questions/5187741/nstimer-on-background-is-working/17445679">can</a> have a timer fire while in background execution mode. There are a couple of tricks:</p> <ul> <li>You need to opt into background execution with <code>beginBackgroundTaskWithExpirationHandler</code>. </li> <li>If you create the NSTimer on a background thread, you need to add it to the mainRunLoop manually.</li> </ul> <hr> <pre><code>- (void)viewDidLoad { // Avoid a retain cycle __weak ViewController * weakSelf = self; // Declare the start of a background task // If you do not do this then the mainRunLoop will stop // firing when the application enters the background self.backgroundTaskIdentifier = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{ [[UIApplication sharedApplication] endBackgroundTask:self.backgroundIdentifier]; }]; // Make sure you end the background task when you no longer need background execution: // [[UIApplication sharedApplication] endBackgroundTask:self.backgroundTaskIdentifier]; dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ // Since we are not on the main run loop this will NOT work: [NSTimer scheduledTimerWithTimeInterval:0.5 target:self selector:@selector(timerDidFire:) userInfo:nil repeats:YES]; // This is because the |scheduledTimerWithTimeInterval| uses // [NSRunLoop currentRunLoop] which will return a new background run loop // which will not be currently running. // Instead do this: NSTimer * timer = [NSTimer timerWithTimeInterval:0.5 target:weakSelf selector:@selector(timerDidFire:) userInfo:nil repeats:YES]; [[NSRunLoop mainRunLoop] addTimer:timer forMode:NSDefaultRunLoopMode]; // or use |NSRunLoopCommonModes| if you want the timer to fire while scrolling }); } - (void) timerDidFire:(NSTimer *)timer { // This method might be called when the application is in the background. // Ensure you do not do anything that will trigger the GPU (e.g. animations) // See: http://developer.apple.com/library/ios/DOCUMENTATION/iPhone/Conceptual/iPhoneOSProgrammingGuide/ManagingYourApplicationsFlow/ManagingYourApplicationsFlow.html#//apple_ref/doc/uid/TP40007072-CH4-SW47 NSLog(@"Timer did fire"); } </code></pre> <p><strong>Notes</strong></p> <ul> <li>Apps only get ~ 10 mins of background execution - after this the timer will stop firing.</li> <li>As of iOS 7 when the device is <em>locked</em> it will suspend the foreground app almost instantly. The timer will not fire after an iOS 7 app is locked.</li> </ul>
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    1. PONSTimer on background IS working
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    1. COGreat peace of code, this will help me finish my app, THNX :). One little question, what do you meen by "This method MIGHT be called when the application is in the background."? I want to use this for updating data from server once in the 3 hours. Is there a better approach?
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    2. COYour application will only run for a maximum of 10 mins when put into the background. As of iOS 7 these 10 mins can be disjoint. You might be able to use use iOS7's new background modes: background transfer for large upload / download or silent push for waking you app up remotely.
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