Question

I’d like to execute my method at midnight, but I haven’t idea how to do this correctly. Check time every minute and if current time is equal 23:59 run method looks stupid. Calculate time interval from now to midnight and set it as parameter to nstimer?

Can you help me with this problem?

UPDATE:
Sorry, guys, I forgot one thing about this: method have to run background without any user notification.

Answer 1

You can use Local Notification:

UILocalNotification *notif = [[UILocalNotification alloc] init];
notif.soundName = @"sound.wav";
notif.alertBody = @"My Message";
notif.alertAction = @"Open";

// you need to configure interval and firedate to schedule everything
notif.repeatInterval = XXX;
notif.repeatCalendar = XXX;
notif.fireDate       = XXX;

[[UIApplication sharedApplication] presentLocalNotificationNow:notif];

[notif release];

To detect when app opened from notification, you need to implement in your App Delegate these methods:

- (void)applicationDidEnterBackground:(UIApplication *)application
- (void)applicationDidBecomeActive:(UIApplication *)application
- (void)applicationWillTerminate:(UIApplication *)application

hope this helps.

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AFTER YOUR EDIT:

You can use [NSTimer ScheduleTimerWith.....] method.