Open Radar

 
Summary:

When a NSManagedObjectContext is saved with both inserts and updates/deletes and an NSFetchedResultsController merges those changes, the NSFetchedResultsControllerDelegate methods are called twice, once for inserts and again for updates/deletes.

This causes a situation where - controllerDidChangeContent: is sent while the fetched results controller is in an intermediate state, having only processed a portion of the changes in the change notification.

I've tested this in both the iPhone Simulator 4.3.2 and on an iPhone running iOS 4.3.5, with identical results.


Steps to Reproduce:

Attached is the CoreDataBooks sample project, updated with a toolbar button that triggers the behavior. Console messages are logged when each delegate method is called.

The steps to reproduce are:

1. Query results using an NSFetchedResultsController
2. Insert a record and update or delete another record in a separate context.
3. Save the context
4. The NSFetchedResultsController will process the change notification and call the delegate methods twice, once for the insert and again for the update/delete.


Expected Results:

- controllerWillChangeContent:
process all inserts, updates, moves, and deletes
- controllerDidChangeContent:

The documentation for NSFetchedResultsControllerDelegate is not explicit that this is the intended behavior, but it does hint at it:

"Rather than responding to changes individually (as illustrated in “Typical Use”), you could just implement controllerDidChangeContent: **(which is sent to the delegate when all pending changes have been processed)** to reload the table view."

I expect the console log from the attached sample app to look like this:

2011-09-29 11:02:51.573 CoreDataBooks[10229:b603] --> content will change
2011-09-29 11:02:51.574 CoreDataBooks[10229:b603] did change object
2011-09-29 11:02:51.575 CoreDataBooks[10229:b603] insert object
2011-09-29 11:02:51.579 CoreDataBooks[10229:b603] did change object
2011-09-29 11:02:51.581 CoreDataBooks[10229:b603] delete object
2011-09-29 11:02:51.584 CoreDataBooks[10229:b603] did change object
2011-09-29 11:02:51.585 CoreDataBooks[10229:b603] update object
2011-09-29 11:02:51.586 CoreDataBooks[10229:b603] --> content did change
2011-09-29 11:02:51.587 CoreDataBooks[10229:b603] fetched objects count: 11


Actual Results:

– controllerWillChangeContent:
process all inserts
– controllerDidChangeContent:

process updates and deletes:
– controllerWillChangeContent:
process all updates, moves, and deletes
– controllerDidChangeContent:

The actual console log from the attached sample app looks like this:

2011-09-29 11:02:51.573 CoreDataBooks[10229:b603] --> content will change
2011-09-29 11:02:51.574 CoreDataBooks[10229:b603] did change object
2011-09-29 11:02:51.575 CoreDataBooks[10229:b603] insert object
2011-09-29 11:02:51.575 CoreDataBooks[10229:b603] --> content did change
2011-09-29 11:02:51.576 CoreDataBooks[10229:b603] fetched objects count: 12
2011-09-29 11:02:51.578 CoreDataBooks[10229:b603] --> content will change
2011-09-29 11:02:51.579 CoreDataBooks[10229:b603] did change object
2011-09-29 11:02:51.581 CoreDataBooks[10229:b603] delete object
2011-09-29 11:02:51.584 CoreDataBooks[10229:b603] did change object
2011-09-29 11:02:51.585 CoreDataBooks[10229:b603] update object
2011-09-29 11:02:51.586 CoreDataBooks[10229:b603] --> content did change
2011-09-29 11:02:51.587 CoreDataBooks[10229:b603] fetched objects count: 11


Notes:

This definitely looks like a bug to me, but if it's the intended behavior, then the documentation should be updated to clearly describe this behavior.


Attachment: http://yaychris.com/radar/10207615/CoreDataBooks.zip



07-Oct-2011 05:15 PM Apple Developer Bug Reporting Team :
Please test this issue with the iOS 5 GM seed (Build #: 9A334) and reply back with your results.

iOS GM seed 9A334
https://developer.apple.com/devcenter/ios/index.action#
Date Posted: October 4th, 2011



10-Oct-2011 10:39 AM Chris Jones:
Built against the iOS 5 SDK in Xcode 4.2 4D199 and tested on the Simulator running 9A334 and experienced the same issue described in this report.