Question

In my app, users purchase consumables, let’s say suitcases, that are stored in Core Data. When the user first installs the app, I give them a freebie to get started. The app can’t function without at least one suitcase set up.

But if the user installs the app on their iPhone and then their iPad and syncs the two, they now have 2 suitcases. And if they uninstall the app on either device, then reinstall and sync it, they’ve just gained an extra one and they can do that indefinitely.

I can see two solutions, but none of them seem right:

1. Add a value to NSUbiquityKeyValueStore when the user first syncs with iCloud. Check this value on first launch. If it’s nil, create the freebie, if it’s not, sync data. But this creates a problem. What if the user disables iCloud or has no internet connection on first launch. The app would create the freebie, then when iCloud is available, sync the duplicate, and they could do this as many times as they like.

2. Somehow match the default items on each app. I had the idea of matching objectIDs or timestamps, but these would vary and I’m not sure how to handle it.

Does anyone know anything I could do about this?

EDIT:

Using a prepackaged database plus migratePersistentStore:toURL:options:withType:error: seems to be the way to go. Will post an answer with code if it works for me.

Answer 1

The best solution to this, in my opinion, is to store UDIDs in an array in iCloud UbiquitousKeyValueStore.

//Store UDID in iCloud
if ([[[UIDevice currentDevice] systemVersion] doubleValue] >= 5.0) {
    if ([[NSFileManager defaultManager] URLForUbiquityContainerIdentifier:nil]) {
        NSUbiquitousKeyValueStore *store = [NSUbiquitousKeyValueStore defaultStore];

        //Get array
        NSMutableArray *devices = [NSMutableArray arrayWithArray:[store arrayForKey:@"UDID"]];
        [devices addObject:[[UIDevice currentDevice] uniqueIdentifier]];

        //Create new array, set to kvstore
        NSArray *newDevices = [NSArray arrayWithArray:devices];
        [store setArray:newDevices forKey:@"UDID"];
        [store synchronize];
    }
}

…

   //Check if app already installed on device
   NSArray *devices = [[NSUbiquitousKeyValueStore defaultStore] arrayForKey:@"UDID"];

    for (NSString *UDID in devices) {
        if ([UDID isEqualToString:[[UIDevice currentDevice] uniqueIdentifier]]) {
              //stop the giveaway
        }
    }