iphone - Prevent app from shutting down when device is rebooted

Question

When I restart the device my app is on it won't preserve the state it had once I open up the app again, it will be as if it's the first time I open, losing the session and having to re-login, how can I make my app preserve its state even through a device reboot? Like Twitter does, for example.

Answer 1

I'll try a bit more formal answer based on the comments you added above. I'll start by saying that the link Tim posted is something you should familiarize yourself with.

When your app is running, it's in the Foreground state. When you "exit" an app with the Home button, you're not really quitting it; you're just pushing it to the Background state. after a few seconds in background state, the OS automatically moves the app to the Suspended state. If you come back within a few minutes, your app is still in memory, so the OS just puts it back on the screen the way it was.

However, if you leave the app alone for a while and use other apps, the OS can--at any time and without warning--purge your app from memory. This is known as the "Not Running" state. Now, when the open the app again, it has to start from scratch. Obviously, the same thing happens when the device restarts--all apps are purged from memory.

The trick, then, is to save essential information about the app state whenever it enters the background state. You can use the app delegate's didEnterBackground method, or register for the UIApplicationDidEnterBackgroundNotification and invoke a method in your active view controller (or any other class, for that matter). Either way, you should save whatever state information you can.

How do you save this information? There are several strategies. For a simple app, perhaps you can register a few setting as NSUserDefaults. Or maybe you can write out a file containing whatever data the user was working on. It's really up to you.

Then, whenever the app launches, check for the presence of that saved data (however you chose to write it out), and set up the UI accordingly. To the user, it will appear as though the app never quit, which is exactly what Apple wants them to think.