Coredata iPhone to iPad/Mac with iCloud?

Question

We have finished writing an iPhone App that uses coredata. In further versions we plan to add an iPad App that is able to display the data collected by the iPhone App (and of corse modify, use it) to give more interaction possibilities to the user.

My question is: Is it possible to move existing coredata (of already installed apps on iphones) to the cloud and read that data out with an iPad application?

If yes: can you point me in the right direction of where to start?

If no: is there another alternative to access coredata created with an iPhone App with an iPad app?

Answer 1

When using Core Data's built in iCloud support it doesn't matter what kind of device you're on, only that the Core Data stack is initialized the same way. Any iOS device or Mac can use the same iCloud store, and data created on one can be read on another.

One crucial detail though: If you already have a data store and you add iCloud support, those pre-existing records do not automatically get migrated to the cloud. iCloud works based on transaction logs, and transaction logs are only created when you save changes. Existing data that doesn't immediately change generates no transactions, and therefore doesn't go to the cloud.

If you have existing data when you add iCloud, you'll need to migrate the data to a new data store to force transactions for those existing records. You can do this fairly easily using NSPersistentStoreCoordinator 's migratePersistentStore:toURL:options:withType:error: method. It's not hard, but it's not always obvious that it's necessary.

To get started, I first suggest watching Apple's WWDC videos on iCloud-- especially WWDC 2012's session 227, Using iCloud with Core Data . Next, I suggest extreme caution, because as of today Core Data's iCloud support is still, shall we say, far from being the most reliable of Apple's APIs.