Styjun

I'm learning CoreData on mac os. I have a demo program which basically works, except that when I delete a row from my tableView,

fetchedResultsController.fetchedObjects?.count

hasn't updated.

Revelevant properties are defined as follows

 var container: NSPersistentContainer!
 var fetchedResultsController: NSFetchedResultsController<Commit>!
 var count: Int get 
 if fetchedResultsController == nil return 0 
 return fetchedResultsController.fetchedObjects?.count ?? 0
 

The remove method:

 func remove(itemAt index: Int) 
 guard let n = fetchedResultsController.fetchedObjects?.count,
 index < n && index >= 0,
 let commit = fetchedResultsController.fetchedObjects?[index] else return 
 container.viewContext.delete(commit)
 saveContext()
 ddt("remove (count)", caller: self)
 

The count after remove hasn't been updated, however the persistent store is correct. If I remove another row, it still doesn't update, but if I change predicate (even to the nil predicate) it refreshes properly.

On relaunch, all is updated.

My delegate doesn't do anything. The table gets updated in its delegate:

 func tableView(_ tableView: NSTableView, rowActionsForRow row: Int, edge: NSTableView.RowActionEdge) -> [NSTableViewRowAction] 
 // left swipe
 if edge == .trailing 
 let deleteAction = NSTableViewRowAction(style: .destructive, title: "Delete", handler: 
 [unowned self] (rowAction, row) in
 self.dataContainer.remove(itemAt: row)
 tableView.removeRows(at: [row], withAnimation: .slideLeft)
 )
 deleteAction.backgroundColor = NSColor.red
 return [deleteAction]
 
 // Anything other than left does nothing
 return []
 

What have I left out?

(ddt, for those too young to remember, was an insecticide banned many years ago because it tended to propagate up the food chain, killing off birds, among other species. I think it's safe to use on bugs in Swift.)

• 
  

  First of all declare the fetchedResultsController as lazy non-optional property and set the delegate in the closure

  
  
  

  lazy var fetchedResultsController: NSFetchedResultsController<Commit> = 
  
   ...
  
   let controller = NSFetchedResultsController( ...
   controller.delegate = self
  
   ...
   return controller
  ()
  

  
  


• 
  

  Adopt NSFetchedResultsControllerDelegate and implement the delegate methods

  
  
  
  • func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>)
  
  
  • func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?)
  
  
  • func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>)
  
  


• 
  

  To delete a record in a NSTableViewRowAction get the item at indexPath and delete the record in the Core Data stack. You don't need to check the index, the row does exist

  
  
  

  let indexPath = IndexPath(item: row, section: 0)
  let commit = fetchedResultsController.object(at: indexPath)
  container.viewContext.delete(commit)
  saveContext()
  

  
  
  

  The NSFetchedResultsControllerDelegate methods manage the update of the UI