Restoring Game Lives using UILocalNotification - objective-c

Question

I am creating a game in Spritekit, and I am trying to set up my game in a way that when a player loses all of their lives they have to wait 30 minutes for one of their lives to be restored so that they can play again. I tried using NSTimer to do this but I figured UINotification will be more effective since I want this timer to run whether or not the app is terminated, in the background, being used or not being used. I'm having problems setting this up though.
I have the following code written thus far, when the user reaches the GameOverScene
-(instancetype)initWithSize:(CGSize)size {
if (GameLives < 5 ) {
alarm = [[UILocalNotification alloc] init];
alarm.fireDate = [NSDate dateWithTimeIntervalSinceNow:thirtyNewMinutes];
alarm.timeZone = [NSTimeZone localTimeZone];
[[UIApplication sharedApplication] scheduleLocalNotification:alarm];
alarm.repeatInterval = NSCalendarUnitHour;
NSLog(#"AlarmFireDate = %#", alarm.fireDate);
}
}
The alarm.firedate shows up correctly in the NSLog when I reach the GameOverScene but when I close down my app and restart it, it shows up as null in my view controllers and never fires. How do I get my app to automatically update the user's lives in the background once the notification is scheduled regardless of whether the user is using the app or not? Should it be run in my app delegate?
Should some type of NSDate comparison like the one below run somewhere?
if ([[NSDate date] compare:allarm.fireDate] == NSOrderedDescending) {
GameLives = GameLives + 1;
NSLog(#"SUCCESS");
NSLog(#"COUNT = %lu", (long)GameLives);
}
else if ([[NSDate date] compare:allarm.fireDate] == NSOrderedAscending){
GameLives = GameLives + 1;
NSLog(#"FAILURE");
NSLog(#"COUNT = %lu", (long)GameLives);
}
else if ([[NSDate date] compare:allarm.fireDate] == NSOrderedSame){
NSLog(#"SAME");
NSLog(#"COUNT = %lu", (long)GameLives);
}
I'd be most grateful to anybody that can offer help.
EDIT: RESPONSE TO THE ANSWERS BELOW
I wrote the following code for the NSTimer and the timer starts when the game reaches the GameOver Scene.
-(void)restoreLives{
thirtyNewMinutes = 60 * 30;
update = [NSDate dateWithTimeIntervalSinceNow:thirtyNewMinutes];
if ([[NSDate date] compare:update] == NSOrderedDescending) {
NSLog(#"date1 is later than date2");
NSLog(#"SUCCESS");
NSLog(#"CurrentDate: %#", [NSDate date]);
// LifeText = #"Restored";
GameLives = GameLives + 1;
NSLog(#"LIVES = %ld", (long)GameLives);
// NSLog(#"Level 2 HighScore, %d", _Level1HighScoreNumber);
} else if ([[NSDate date] compare:update] == NSOrderedAscending) {
NSLog(#"date1 is earlier than date2");
NSLog(#"FAILURE");
NSLog(#"CurrentDate: %#", [NSDate date]);
NSLog(#"LIVES = %ld", (long)GameLives);
// Lives = 5;
// NSLog(#"dates are the same");
}
if (GameLives < 4){
[LifeTimer invalidate];
}
And then I created an NSTimer to run the method.
-(void)CheckTime{
LifeTimer = [NSTimer scheduledTimerWithTimeInterval:0.01 target:self selector:#selector(restoreLives) userInfo:nil repeats:YES];
}
How would I get it to save the target time that you're speaking of?
And, hopefully I'm not overthinking this but from another perspective if I wanted to compare the current NSDate with the [NSDate dateWithTimeIntervalSinceNow:thirtyNewMinutes]; wouldn't I need to save the original date of [NSDate dateWithTimeIntervalSinceNow:thirtyNewMinutes]; when it was originally called so that if the app terminates and the timer runs the code again it compares it to the original time the code was called and doesn't reset the NSDate and compare it to 30 minutes from the time the user restarts the app and the timer begins again.
i.e. 7:15
NSDate comparison to update = [NSDate dateWithTimeIntervalSinceNow:thirtyMinutes];
is called. And timer is set to update lives at 7:45.
7:30 User terminates their app and restarts it at 7:35
When the NSTimer runs again won't it reset the time to be 30 minutes from 7:35 since it's 30 minutes from now? If this is the case how would I go about saving the original date? Please let me know, keep in mind I'm still a beginner with Objective C

Answer 1

A local notification works well if you want to inform the user of something, and can have a payload which you could use to keep track of the information you need, but it's probably not the best solution for you to do your timing work. If the user disables notifications for your app, it would break your functionality.
Instead, when it comes to keeping track of events based on a time, it's best to rely on date comparisons along with timers.
While your app is open, you should use an NSTimer to trigger what you need to do, which I think you have covered.
When you app goes to the background or terminates you should save the target time in some kind of persistent storage (NSUserDefaults, for example). When you app is relaunched or returns from the background, you should compare against that date and either start up the timer or trigger your code that the timer would fire yourself.
Try this to save/restore the date:
// Save the date with the key "NextFireDate"
[[NSUserDefaults standardUserDefaults] setObject:nextFireDate forKey:#"NextFireDate"];
// This forces the values to be saved by the system, which normally only happens periodically
[NSUserDefaults standardUserDefaults] synchronize];
...
// Retrieve the date with the key "NextFireDate"
NSDate *nextFireDate = [[NSUserDefaults standardUserDefaults] objectForKey:#"NextFireDate"];
You'd call the first whenever you go to the background/terminate (also invalidate your current timer) and the second when you finish launching or return from the background (and start a new timer with the retrieved date). NSUserDefaults is basically just a dictionary (that can accept scalars without having to box them yourself) that persists as long as your app is installed.