How do I properly manage iCloud files via NSFileManager?

Question

I am attempting to add iCloud synching to my iOS/Mac app by using the iCloud methods on NSFileManager (no documents or file coordinators). The app needs to synch audio files across the various instances; create, delete and metadata changes. It isn't a collaboration style app, so I am not very worried about conflicts, etc. I have something basic working, but have run into some basic questions that I can't seem to find definitive answers to.

1. When using iCloud, there are two local directories involved, the sandbox directory where the file originates and the ubiquity container directory. Once I enable a file for ubiquity, should I start interacting with the file in the ubiquity container directly or should I continue interacting with the sandbox file and pushing/pulling changes from the ubiquity counterpart? It feels like the latter is best so that I don't lose all the users files if they turn iCloud off (not sure what happens to files in ubiquity container in that case).

2. If I maintain two files, is there a preferred way to push/pull incremental changes to/from the ubiquity container? As I understand it, if a user changes a file on a given device, all other devices get the incremental changes in their local ubiquity copy (if downloaded). Should I just be copying the file in it's entirety over to my local sandbox directory every time the ubiquity file changes and vice versa?

Answer 1

Constantly copying files to the ubiquity container as they are modified doesn't seem like a good strategy to me and might even result in iCloud thinking more of the file has changed than really has. You can interact with files in the ubiquity container directly, working with them just as you would a file in your 'normal' document sandbox. This is the model prescribed in all of the iCloud documentation, sparse as it may be.

You're right that you need to be able to handle the situation where a user migrates away from iCloud. There are methods to move a file out of the ubiquity container and some of the newer iOS 6 API makes it easier to detect if the user has iCloud enabled, though this is still an area where we could use more API.