问iOS 7后台计时器

EN

CLLocationManager * manager = [[CLLocationManager alloc]init];
__block UIBackgroundTaskIdentifier background_task;

background_task = [application beginBackgroundTaskWithExpirationHandler:^ {
    [application endBackgroundTask: background_task];
    background_task = UIBackgroundTaskInvalid;

}];

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

    [manager startUpdatingLocation];

    while(TRUE)
    {
        //backgroundTimeRemaining time does not go down.

        NSLog(@"Background time Remaining: %f",[[UIApplication sharedApplication] backgroundTimeRemaining]);
        [NSThread sleepForTimeInterval:1]; //wait for 1 sec
    }

    [application endBackgroundTask: background_task];
    background_task = UIBackgroundTaskInvalid;
});