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I have an iOS 7 app, that is using Core Data. Some of the Core Data objects has a related (one to one relationship) images that are > 1MB & < 4MB and are stored in the app’s Document folder. Core Data objects only stores image names as string.

I want to integrate iCloud support for the app so I can sync data between devices. I am planning to use iCloud Core Data storage to sync Core Data objects. But what to do with the images?! After reading different posts, I found a couple of options that are highlighted underneath. I am struggling to pick one, that would suit me best. It would be nice to know someones experience/recommendations. What I should be careful with, or what didn't I think of? I also need to consider migration of the existing data to the option I will pick.

OPTION 1. Store UIImage in the Core Data as Binary Data with External Binary Data option (read here). At this moment is seems to be the easiest solution, but I guess not the best. From Documentation:

It is better, however, if you are able to store BLOBs as resources on the filesystem, and to maintain links (such as URLs or paths) to those resources.

Also will the external files be synced? If so, how reliable the sync would be if the user quits on minimises the app, will the sync process resume? From objc.io about External File References:

In our testing, when this occurs, iCloud does not always know how to resolve the relationship and can throw exceptions. If you plan to use iCloud syncing, consider unchecking this box in your iCloud entities

OPTION 2. Store images using UIDocument (good tutorial here) and somehow track relation between Core Data entry and UIDocument. From what I understand whatever I put in this directory will be automatically synchronised to the iCloud by a system daemon. So if the user quits the app, the images will still be synced to the iCloud, right?

OPTION 3. Using FileManager(more info here). I haven’t read a lot about this approach, but I think it can also work.

OPTION 4. Any other?

There are similar posts (e.g. Core Data with iCloud design), but unfortunately they don't fully answer my question.

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sash
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1 Answers1

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Seems Apple will reject application because of large database iCloud synchronization.

I think the best solution is to store images on a remote host, and keep Image URL in CoreData.
And also Local path of image should be resolvable from remote URL.

So the algorithm will look like this ->
1) Getting Remote URL from CoreData.
2) Resolve local path of image.
3) If local image exists retrieve it, otherwise read it from remote and save it to local storage.

You can have a look to Amazon S3 server here.

l0gg3r
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  • Thanks for the answer. Why would be the app rejected? It depends on the user of the app how much data he will use. – sash Nov 04 '14 at 09:04
  • This article covers rejections http://www.icapps.com/prevent-app-rejection-caused-by-icloud-storage/ – l0gg3r Nov 04 '14 at 12:12