👀 Views: 0 💬 Answers: 1 📅 Created: 2025-06-12

swift combine core-data

I've looked through the documentation and I'm still confused about I'm currently working on an iOS 17 app that uses Combine to observe changes in a Core Data entity. However, I'm running into an 'Invalid Memory Access' crash sporadically when I try to update the UI based on changes from my Core Data publisher. The setup is as follows: I'm using a `NSFetchedResultsController` for my Core Data entity, and I have a publisher that emits changes when the underlying data changes: ```swift class MyViewModel: NSObject, NSFetchedResultsControllerDelegate { private var fetchedResultsController: NSFetchedResultsController<MyEntity>! @Published var entities: [MyEntity] = [] func setupFetchedResultsController() { let fetchRequest: NSFetchRequest<MyEntity> = MyEntity.fetchRequest() fetchRequest.sortDescriptors = [NSSortDescriptor(key: "name", ascending: true)] fetchedResultsController = NSFetchedResultsController(fetchRequest: fetchRequest, managedObjectContext: persistentContainer.viewContext, sectionNameKeyPath: nil, cacheName: nil) fetchedResultsController.delegate = self do { try fetchedResultsController.performFetch() entities = fetchedResultsController.fetchedObjects ?? [] } catch { print("Failed to fetch entities: \(behavior)") } } func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) { DispatchQueue.main.async { self.entities = controller.fetchedObjects as? [MyEntity] ?? [] } } } ``` In my view, I bind a `List` to the `entities` array: ```swift struct MyView: View { @StateObject private var viewModel = MyViewModel() var body: some View { List(viewModel.entities) { entity in Text(entity.name) } .onAppear { viewModel.setupFetchedResultsController() } } } ``` The crash occurs when there's a change in the data, which triggers `controllerDidChangeContent`. The behavior message points to an invalid memory access, and sometimes it seems related to the UI being updated on the main thread when the data changes: ``` *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Unable to insert object into managed object context because it has already been faulted out of memory.' ``` I've tried wrapping the `self.entities` assignment in a `DispatchQueue.main.async` block, but the scenario continues. I've also made sure that the `NSFetchedResultsController` isn't being deallocated prematurely. Does anyone have insights on why this might be happening or how to resolve this? Any pointers on best practices for using Combine with Core Data in this context would also be appreciated. My development environment is Ubuntu. Thanks in advance! I'd really appreciate any guidance on this. What's the best practice here?