So I've been doing a bit of research on how to tell if it's a new day in my iOS app. Basically, I want to reset a bunch of values to 0 as soon as a new day starts. I've seen that I can use "UIApplicationSignificantTimeChangeNotification" which sends a notification at midnight. However, will this still fire if the user killed the app at 9:00AM and opens it up again at 9:00AM the next day?
I also saw that I could use "NSCalendarDayChangedNotification" which to my understanding has the same behavior. My only concern is that if either of these will accomplish detecting a day change even after the user kills the app.
Ideally I'd like to put add the notification observer at the top of my .m file in the viewDidLoad like so:
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(resetValues) name:UIApplicationSignificantTimeChangeNotification object:nil];
and then somewhere else in the file...
- (void)resetValues {
... // reset values to 0
}
The goal would be for this notification to trigger at the beginning of every day change. Would the code above achieve the behavior I'm looking for?
Solution which saves an integer value (the day) in NSUserDefaults
In AppDelegate create a method checkDayChange which compares the day component of the current date with a saved value in NSUserDefaults (default is 0). If the values are not equal, call resetValues and save the current day.
- (void)checkDayChange
{
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSInteger currentDay = [[NSCalendar currentCalendar] component:NSCalendarUnitDay fromDate:[NSDate date]];
NSInteger savedDay = [defaults integerForKey:@"day"]; // default is 0
if (currentDay != savedDay) {
[self resetValues];
[defaults setInteger:currentDay forKey:@"day"];
}
}
Observe NSCalendarDayChangedNotification with selector checkDayChange
checkDayChange also in applicationDidFinishLaunching and applicationDidBecomeActive