Add these properties to your .h file
@property (nonatomic, strong) NSTimer *updateTimer;
@property (nonatomic) UIBackgroundTaskIdentifier backgroundTask;
Now replace btnStartClicked method with this,
-(IBAction)btnStartClicked:(UIButton *)sender {
self.updateTimer = [NSTimer scheduledTimerWithTimeInterval:0.5
target:self
selector:@selector(calculateNextNumber)
userInfo:nil
repeats:YES];
self.backgroundTask = [[UIApplication sharedApplication] beginBackgroundTaskWithExpirationHandler:^{
NSLog(@"Background handler called. Not running background tasks anymore.");
[[UIApplication sharedApplication] endBackgroundTask:self.backgroundTask];
self.backgroundTask = UIBackgroundTaskInvalid;
}];
}
-(void)calculateNextNumber{
@autoreleasepool {
// this will be executed no matter app is in foreground or background
}
}
and if you need to stop it use this method,
- (IBAction)btnStopClicked:(UIButton *)sender {
[self.updateTimer invalidate];
self.updateTimer = nil;
if (self.backgroundTask != UIBackgroundTaskInvalid)
{
[[UIApplication sharedApplication] endBackgroundTask:self.backgroundTask];
self.backgroundTask = UIBackgroundTaskInvalid;
}
i = 0;
}