Careful Devs’! Changes to Apple’s iOS Data Storage Guidelines could get your app rejected.

Apple recently sent an email to developers whose apps were making inefficient use of iCloud’s backup settings. The email asked developers to review the amount and type of data the app was storing in its Documents folder, as iCloud backs up all app data stored in the Documents directory when the Documents & Data backup option is set to “On”. Seeing as this setting covers all apps, it is especially important to ensure that only documents and other data that are user-generated, or that cannot otherwise be recreated by the app, should be stored in the /Documents Directory. Most importantly, Apple is telling developers to get their apps in-line with the new iOS Data Storage Guidelines, and submit an update.

Before iCloud, users backed up their devices through iTunes to their computers. Now contacts, music, and apps are backed up to iCloud over WiFi or 3G. In order to improve user experience, Apple has made a small yet significant change to its iOS Data Storage Guidelines. As of iOS 5.0.1, a new “do not backup” file attribute was introduced, allowing developers to clearly specify how files should be treated in the following scenarios:

• "Temporary data" (that which can be reconstructed during normal operation) must be stored in the "Cache" or "tmp" directories.  The OS will delete files in these locations when the user is running out of storage space on their device.
• "User data" (that which can't be reconstructed automatically) must be stored in the Documents directory and will be backed up to iCloud.
• "Offline data" (that which the user has some reasonable expectation to have available when disconnected from network access, but which shouldn't take up valuable back-up space) must be stored in the Documents directory and marked as "do not back up".

By using this new attribute and placing files in the right place, files can be described as one of four data categories: critical data, cashed data, temporary data, and offline data.

Developers whose apps cache content for offline viewing or who currently cache certain assets which are integral to the functionality of the app offline, need to be aware that caches are now being cleared in low-memory situations, and after iCloud backups. Content stored in the cache needs to be easily re-downloadable or stored as “Offline data” in the Documents directory and marked as “do not back up”.

Since the release of iOS 5.0.1, all apps being submitted to the App Store that do not comply with this new change to the Apple iOS Data Storage Guidelines will be rejected. In particular, storing “Temporary data” or “Offline data” in the Documents folder without the “do not backup” attribute is a rejection-able offense.

For more information, see this article on the data handling categories.