NSFetchedResultsController XCode 7 issue

Question or problem in the Swift programming language:

Xcode 7 beta 6 and and NSFetchedResultsController gave me headache today. If I compile same(with Swift 2 fixes) code with Xcode 6, program works on device and simulators(iOS 7, iOS8). However if I compile with Xcode 7 beta 6, program crashes on device(iOS 8.4) with following error messages whenever I update Core Data.

I get an error similar to below

Sometimes it crashes with another error like

//NSFetchedResultsController delegates



func controllerWillChangeContent(controller: NSFetchedResultsController) {
    self.tableView.beginUpdates()
}

func controller(controller: NSFetchedResultsController, didChangeSection sectionInfo: NSFetchedResultsSectionInfo, atIndex sectionIndex: Int, forChangeType type: NSFetchedResultsChangeType) {
    switch type {
    case .Insert:
        self.tableView.insertSections(NSIndexSet(index: sectionIndex), withRowAnimation: .Fade)
    case .Delete:
        self.tableView.deleteSections(NSIndexSet(index: sectionIndex), withRowAnimation: .Fade)
    default:
        return
    }
}

func controller(controller: NSFetchedResultsController, didChangeObject anObject: AnyObject, atIndexPath indexPath: NSIndexPath?, forChangeType type: NSFetchedResultsChangeType, newIndexPath: NSIndexPath?) {
    switch type {
    case .Insert:
        print("Insert New: \(newIndexPath) Old: \(indexPath)")
        tableView.insertRowsAtIndexPaths([newIndexPath!], withRowAnimation: .Fade)
    case .Delete:
        print("Delete New: \(newIndexPath) Old: \(indexPath)")
        tableView.deleteRowsAtIndexPaths([indexPath!], withRowAnimation: .Fade)
    case .Update:
        print("Update New: \(newIndexPath) Old: \(indexPath)")
        tableView.reloadRowsAtIndexPaths([indexPath!], withRowAnimation: .Fade)
        //self.configureCell(tableView.cellForRowAtIndexPath(indexPath!)!, atIndexPath: indexPath!)
    case .Move:
        print("Move New: \(newIndexPath) Old: \(indexPath)")
        tableView.deleteRowsAtIndexPaths([indexPath!], withRowAnimation: .Fade)
        tableView.insertRowsAtIndexPaths([newIndexPath!], withRowAnimation: .Fade)
    }
}

func controllerDidChangeContent(controller: NSFetchedResultsController) {
    self.tableView.endUpdates()
}

for the .Update section I also tried to call

 self.configureCell(tableView.cellForRowAtIndexPath(indexPath!)!, atIndexPath: indexPath!)

Configure cell method:

func configureCell(cell: UITableViewCell, atIndexPath indexPath: NSIndexPath) { 
   let object = self.fetchedResultsController.objectAtIndexPath(indexPath) as! Person 
   //etc 
} 

Sort Descriptors

let sortDescriptor = NSSortDescriptor(key: "date", ascending: false)
fetchRequest.sortDescriptors = [sortDescriptor]

Program always crashes. Only way to somehow stop this issue is setting delagete to nil, update object and set delagate back to self.

Is this a bug? If it isn’t, how can I prevent this? Thanks

Some bug reports with same/similar issue

https://forums.developer.apple.com/thread/12184

https://forums.developer.apple.com/thread/4999

iOS 9 – “attempt to delete and reload the same index path”

I ran both XCode6 and XCode7 versions and printed didChangeObject method here is the comparison

XCode6 iOS 8.4

Update New: Optional( {length = 2, path = 0 - 0}) Old: Optional( {length = 2, path = 0 - 0})

XCode 7b6 iOS 8.4

Update New: nil Old: Optional( {length = 2, path = 0 - 0})
Insert New: Optional( {length = 2, path = 0 - 0}) Old: Optional( {length = 2, path = 0 - 0})

2015-09-01 01:15:37.898 TestProg[3230:200562] *** Assertion failure in -[UITableView _endCellAnimationsWithContext:], /SourceCache/UIKit/UIKit-3347.44.2/UITableView.m:1623
2015-09-01 01:15:37.900 TestProg[3230:200562] CoreData: error: Serious application error.  An exception was caught from the delegate of NSFetchedResultsController during a call to -controllerDidChangeContent:.  Invalid update: invalid number of rows in section 0.  The number of rows contained in an existing section after the update (3) must be equal to the number of rows contained in that section before the update (3), plus or minus the number of rows inserted or deleted from that section (1 inserted, 0 deleted) and plus or minus the number of rows moved into or out of that section (0 moved in, 0 moved out). with userInfo (null)

How to solve the problem:

Solution 1:

I have tried several things and I believe this is a bug. As you can see from my log, even though I update existing record, delegate gets Insert Message. Adding conditional check at .Insert fixed my issue. I am not using any move operation in the table. Therefore same kind of conditional operation maybe necessary as well if you are using .Move My Current code is like below

func controller(controller: NSFetchedResultsController, didChangeObject anObject: AnyObject, atIndexPath indexPath: NSIndexPath?, forChangeType type: NSFetchedResultsChangeType, newIndexPath: NSIndexPath?) {
    switch type {
    case .Insert:
        //FIXME: iOS 9 Bug!
        if indexPath != newIndexPath {
            tableView.insertRowsAtIndexPaths([newIndexPath!], withRowAnimation: .Fade)
       }
    case .Delete:
        tableView.deleteRowsAtIndexPaths([indexPath!], withRowAnimation: .Fade)
    case .Update:
       tableView.reloadRowsAtIndexPaths([indexPath!], withRowAnimation: .Fade)
        // self.configureCell(tableView.cellForRowAtIndexPath(indexPath!)!, atIndexPath: indexPath!)

    case .Move:
        tableView.deleteRowsAtIndexPaths([indexPath!], withRowAnimation: .Fade)
        tableView.insertRowsAtIndexPaths([newIndexPath!], withRowAnimation: .Fade)
    }
}

I have tried to update single record, multiple records and I haven’t seen any crashes yet so far. I am using

tableView.reloadRowsAtIndexPaths([indexPath!], withRowAnimation: .Fade)

method but

self.configureCell(tableView.cellForRowAtIndexPath(indexPath!)!, atIndexPath: indexPath!)

also worked during my tests.

Solution 2:

This seems to be happening to me when running on Sim/Device < iOS9 using Xcode 7 beta 6:

2015-09-01 11:39:05.683 Diabetes Pal[15038:245613] *** Assertion failure in 
-[UITableView _endCellAnimationsWithContext:], /SourceCache/UIKit_Sim/UIKit-3347.44.2/UITableView.m:1623
2015-09-01 11:39:14.954 Diabetes Pal[15038:245613] CoreData: error: Serious application error.  
An exception was caught from the delegate of NSFetchedResultsController during a call to 
-controllerDidChangeContent:.  Invalid update: invalid number of rows in section 0.  The number of rows contained in an existing section after the update (4) must be equal to the number of rows contained in that section before the update (4), plus or minus the number of rows inserted or deleted from that section (1 inserted, 0 deleted) and plus or minus the number of rows moved into or out of that section (0 moved in, 0 moved out). with userInfo (null)
Diabetes Pal(15038,0x33291d4) malloc: *** mach_vm_map(size=1048576) failed (error code=3)
*** error: can't allocate region securely
*** set a breakpoint in malloc_error_break to debug

A possible workaround is to not animate the changes (until this is fixed):

//MARK: - fetched results controller delegate

func controllerWillChangeContent(controller: NSFetchedResultsController) {
    let ios9 = NSOperatingSystemVersion(majorVersion: 9, minorVersion: 0, patchVersion: 0)
    if NSProcessInfo().isOperatingSystemAtLeastVersion(ios9) {
        tableView?.beginUpdates()
    }
}

func controller(controller: NSFetchedResultsController, didChangeSection sectionInfo: NSFetchedResultsSectionInfo, atIndex sectionIndex: Int, forChangeType type: NSFetchedResultsChangeType) {        
    let ios9 = NSOperatingSystemVersion(majorVersion: 9, minorVersion: 0, patchVersion: 0)
    if NSProcessInfo().isOperatingSystemAtLeastVersion(ios9) == false {
        return
    } //[... rest of delegate implementation ...]
}

func controller(controller: NSFetchedResultsController, didChangeObject anObject: AnyObject, atIndexPath indexPath: NSIndexPath?, forChangeType type: NSFetchedResultsChangeType, newIndexPath: NSIndexPath?) {

    let ios9 = NSOperatingSystemVersion(majorVersion: 9, minorVersion: 0, patchVersion: 0)
    if NSProcessInfo().isOperatingSystemAtLeastVersion(ios9) == false {
        return
    }//[... rest of delegate implementation ...] 
}

func controllerDidChangeContent(controller: NSFetchedResultsController) {
    let ios9 = NSOperatingSystemVersion(majorVersion: 9, minorVersion: 0, patchVersion: 0)
    if NSProcessInfo().isOperatingSystemAtLeastVersion(ios9) == false {
        tableView?.reloadData()
        return
    }
    tableView?.endUpdates()
}

Solution 3:

I did not see this problem any more when I build upon SDK 9.1. It seems the bug have been fixed. You can try it.

Hope this helps!