UILocalNotification show countdown timer on startup or viewdidload - ios

Question

I'm working on app that sets an UILocalNotification. This is the first time I use it and I'd like to have some explanations to use it efficiently and in the best way.
Which is the bast way to countdown to the time of notification expiration? I'd like to show to the user an UILabel with the missing time, this UILabel updates every second and when I reopen my app it must show the timer.
I've done this in this way:
When I reopen my app or the recall the view that has to show the timer I check if there is a UILocalNotification with the userInfo I've setted previously then I subtract to its NSDate
the current time so I get the difference, and update the UILabel. I know it shows time in seconds but if this procedure it's good I will convert it into time.
Is there any best way to do this?
Here is my code:
UILocalNotification *countDownNotificationSetted;
NSArray *scheduledNotificationArray = [[UIApplication sharedApplication] scheduledLocalNotifications];
for (int i = 0; i<[scheduledNotificationArray count]; i++)
if ([[[[scheduledNotificationArray objectAtIndex:i] userInfo] objectForKey:#"ID"] isEqualToString:#"ParkNotification"]) {
countDownNotificationSetted = [scheduledNotificationArray objectAtIndex:i];
break;
}
NSDate *expringDate = [countDownNotificationSetted fireDate];
NSTimeInterval timeLeftToNotification = [expringDate timeIntervalSinceNow];
if(timeLeftToNotification == 0){
[countDownTimer invalidate];
}
datePicker.countDownDuration = timeLeftToNotification;
_countDownLabel.text = [NSString stringWithFormat:#"%.0f", timeLeftToNotification];
NSLog(#"%.0f", timeLeftToNotification);

Answer 1

I think it would be better if you would update your label with a timer as you already do , when you close the app, store that time locally in a file or user defaults and when the app launches again read from that file the time. Or if you want the time passed since the first openning of the app, just write the time in appDidFinishLaunching and get it from there every time . I don't see the benefit of the local notification here.
Hope this helps.
Cheers!