Question

According to apple’s iCloud docs:

Every user with an Apple ID receives a free iCloud account but some users might choose not to enable iCloud for a given device. Before you try to use any other iCloud interfaces, you must call the URLForUbiquityContainerIdentifier: method to determine if iCloud is enabled. This method returns a valid URL when iCloud is enabled (and the specified container directory is available) or nil when iCloud is disabled.

If URLForUbiquityContainerIdentifier: returns nil, then I presume you have to save to the user’s documents directory. What are you supposed to do if the user enabled iCloud at a later date? The docs only tell you what to do when everything goes to plan, but make no mention of best practices for handling anything else… What if iCloud gets disabled, will the local copy of the icloud document get deleted, or have it’s permissions removed from the sandbox?

Answer 1

You should save the state of iCloud enablement (i.e. were you able to get a nonnil result from URLForUbiquityContainerIdentifier:), register for notifications of changes to the situation, etc. If you detect that the state has changed from off to on, the solution is simple; call setUbiquitous:itemAtURL:destinationURL:error: to copy the file from your world into the ubiquity world (it’s just a folder, after all).

This situation is pretty well covered in the docs:

http://developer.apple.com/library/mac/#documentation/General/Conceptual/iCloudDesignGuide/Chapters/iCloudFundametals.html

Unfortunately, if you detect the opposite (the user has turned off iCloud), the file is lost and you can’t retrieve it, because, ex hypothesi, URLForUbiquityContainerIdentifier: is now returning nil. But it is still in the cloud. I presume you could provide interface for asking the user to turn iCloud back on, and more interface for letting the user request that the file be moved back into the nonubiquity world.