I'm reading many things about Local Notifications and the way they can help to update the app badge number.
I'd like to update this badge at midnight, and set its value to a number I can't know before midnight. So I'd like, if possible, to launch a function at midnight that would update/load some datas, check the number to display, and display it on the badge.
Of course, the number to display is not relative to the displayed number, and can be lower or greater.
This is expected to work : - When app is in background - When app is in foreground - When app is not launched
would you know a way to do this, even partially ? If not possible, let say I can make things to know the badge number before midnight... Would this help you for a working answer ? This is not wanted, but if I don't have the choice to make this work, I'll plan to write tons of useless code to do this...
Unless your application fits into one of the "official" multitasking cases (VOIP, location, and background audio), the only way you're going to be able to dynamically set the badge number when your application isn't running is with push notifications... applications can't run code in response to a local notification (until the user presses the "View" button in the notification popup, at least).
See this document for everything you could ever want to know about local and push notifications in iOS.
You can't reliably ensure that your local app will run when it needs to unless you register it as a VoIP app or as requiring continuous location monitoring; either of these, in an app that's not in fact used for VoIP or navigation, will almost certainly result in an App Store rejection.
Your best bet is to send the badge as a push notification. Assuming that a server you control can know what the badge number is supposed to be, it can send a notification with just that badge value—not necessarily an alert popup or sound—to your app. Urban Airship is a good, simple way to send push notifications without having to do a lot of configuration and setup.
You very well may be able to do this. Look at the Apple Guide to running code in the background.
来源：https://stackoverflow.com/questions/4846787/updating-application-badge-at-midnight-with-options-app-not-launched-or-in-back