IOS: store an array with NSUserDefault

Question

I want to store an array with NSUserDefault, then, I put in applicationDidEnterBackground

[[NSUserDefaults standardUserDefaults] setObject:myArray forKey:@"myArray"];

and in application didFinishLaunchingWithOption

myArray= [[NSMutableArray alloc] 
          initWithArray:[[NSUserDefaults standardUserDefaults] 
           objectForKey:@"myArray"]];

it's ok for multitasking device, but for not-multitasking device, how can I solve?

Answer 1

Store the object in NSUserDefaults in -applicationWillTerminate:, if it hasn't already been saved by the invocation of -applicationDidEnterBackground: (i.e. check if multitasking is supported, if it is, then don't save it because it's already been saved.)

- (void) applicationWillTerminate:(UIApplication *) app {
    if([[UIDevice currentDevice] respondsToSelector:@selector(isMultitaskingSupported)] &&
       ![[UIDevice currentDevice] isMultitaskingSupported]) {
       [[NSUserDefaults standardUserDefaults] setObject:myArray forKey:@"myArray"];
    }
}

Answer 2

Do not forget to sync the buffer before going into background:

[[NSUserDefaults standardUserDefaults] synchronize];

Answer 3

The previous answers are all correct, but note that neither applicationDidEnterBackground nor applicationWillTerminate are guaranteed to be called in all situations. You are usually better off storing important data whenever it has changed.