How to wait until cloud kit data is being synced with core data in swift in iOS13

Question

I developed core data based app and implemented iCloud sync feature after it was introduced in iOS 13.

I enabled iCloud kit, used NSPersistentCloudKitContainer instead of NSPersistentContainer and added several lines of code to sync core data with iCloud.

Sync works fine. The problem is that when I uninstall app and reinstall app, it doesn't fetch iCloud data at first time. I have to restart app or open another screens to let Core Data to be synced with iCloud. Is there anyway I can check if core data is being synced with iCloud or wait until it finishes syncing?

Thanks.

Pirozzo

I delayed displaying the main view from SceneDelegate and icloud data showed up. definitely would love an answer on how to wait for icloud sync – Philpott

Just be aware that iCloud has been experiencing various issues since a couple days ago. This could be it. – Crary

I do it the same as @BokuWaTaka. Is there any way to monitor the syncing status? – Amphichroic

In iOS 14 there is a new event you can listen to: NSPersistentCloudKitContainer.eventChangedNotification, how to use it is described in this answer: link – Eloisaeloise

Answer 1

There is no API exposed to get the completion handler on sync of all CKRecord's to NSManagedObject's.

Also the update is working using a background silent notification so we can expect any change anytime. So its good to not having completion handler

What's next

You can create one attribute to check the sync time, just like a date when last sync happened to local record and check the lastModificationDate (By default CKRecord has this property) of the same record in iCloud.

So everytime when you launch the app check for all the records manually if any update is required, then wait for notification of update and keep on checking the sync status

Note: Be careful this may lead to delay your launch process if from any other device user is very active and new records are getting inserted or modified.

Narbonne

When the data is synced, there is logs. Is there any way to read the log for checking the status? – Amphichroic

Answer 2

Currently, there is no API provided for iCloud sync completion. What you can do is

• You can initialize NSPersistentCloudKitContainer and call it's loadPersistentStores() at the start of the app. This will buy you enough time and your data will be available for your internal screens.

• You can also listen for remote changes in your local store and update your UI accordingly as mentioned in this Apple doc: https://developer.apple.com/documentation/coredata/consuming_relevant_store_changes

Trinidad

"this will buy you enough time" is not going to be a good solution here, as unfortunately slow network connections and other interruptions will make this solution unreliable – Ligament

Answer 3

I have to restart app or open another screens to let Core Data to be synced with iCloud.

To solve this I'm using a notification observer for NSManagedObjectContextObjectsDidChange event.

When reinstalled app is first opened, it shows empty screen and after some time, when data is synced, the notification is triggered and the page is reloaded with the data.

However I also couldn't find any way to wait and show loading message while data is being synced.

Scruff