I have a couple of places in my SwiftUI app where I need to fetch a (growing) set of information from CoreData and process it before updating the UI.
I am using the MVVM approach for this and so have a number of NSFetchedResultsController instances looking after fetching and updating results.
In order to stop blocking the main thread as much I tried shifting the NSFetchedResultsController to perform its work on a background thread instead.
This works but only if I disable the -com.apple.CoreData.ConcurrencyDebug 1 argument to ensure I'm not breaching threading rules.
I am already ensuring that all CD access is done on the background thread however it appears that when the SwiftUI view accesses a property from the CD object it is doing so on the main thread and so causing a crash.
For now I can think of a couple of possible solutions:
- Ensure that the data fetched by the NSFetchedResultsController can be fetched/processed in a small amount of time to ensure the UI doesn't hang
- Make "DTO" objects so that data fetched is then inserted into another class instance inside the background thread and have the UI use that.
- The issue with this approach is then making edits or reacting to updates on the object become a lot more convoluted as you need to manually keep the CD and the DTO objects in-sync.
