This is a very theoretical question, but quiet important for me, how I approach my next steps.
I am developing a SwiftUI MacOS app, where a user can upload own files. The metadata getting stored in CoreData and the file I store manually in the file system. At the moment I am using the default file folder for my application.
Soon I want to have a iCloud sync between my Mac OSX app and my iOS app. I read about it and it should work. CoreData should be no problem.
Now to my question if it will be possible to approach it that way I am thinking of:
I would like to create a Finder Sync Extension for my Mac OSX app, so I get a own folder, which can be added to the favorites and be observed. I want all my local files to be stored there. That should work..
I am not storing my documents in a Data blob of the CoreData or allowing External Storage. I store all manually. Will I am able to still sync my documents via iCloud.
All in all, I want to know if I can store my files in the Finder folder, and still keep them synced with iCloud to iOS? If that is not possible, please let me know. Would be interesting to know in forehand.
A Finder Sync Extension should not "do" any syncing. In fact, Apple specifically recommends that a separate background process be used for any networking-like activity:
It’s generally best if the extension focuses on handling the badges, contextual menus, and toolbar buttons. Place in a separate service (a Login Item or Launch Agent) any code that performs the sync, updates state, or communicates with remote data sources. This approach ensures that there is only one syncing service running at a time.
A Finder Sync Extension is used to provide file badges, menus, and otherwise modify the UI of Finder.
Adding a Finder extension doesn't give you a folder, let alone one that syncs.
You need to provide the folder and all sandbox details related to that. Your main app and/or background process needs to provide the syncing service.
In summary, your main app handles all of the syncing.
The Finder Extension only updates the UI for certain folders. It doesn't provide any syncing itself. So any "syncing with iCloud" question you have should be asked independently of the Finder Sync Extension context.