Diffable Data source with more than one section using core data

WWDC 2019 was really packed with new stuff for iOS and the new data sources for TableViews and CollectionView which is UITableViewDiffableDataSource .

I have successfully integrate the above new data source with Core data , delete and insert new record working without any issue , unfortunately I have an issue with move items from section to another , the issue appears if I'm trying to move the last cell in the section .

Below is my code :

Table View Setup

private func setupTableView() {
       diffableDataSource = UITableViewDiffableDataSource<Int, Reminder>(tableView: remindersTableView) { (tableView, indexPath, reminder) -> UITableViewCell? in
           let cell = tableView.dequeueReusableCell(withIdentifier: "SYReminderCompactCell", for: indexPath) as! SYReminderCompactCell
        var reminderDateString = ""
        let reminderTitle = "\(reminder.emoji ?? "") \(reminder.title  ?? "")"

        if let date = reminder.date {// check if reminder has date or no , if yes check number of todos and if date in today
            let dateFormatter = SYDateFormatterManager.sharedManager.getDateFormaatter()
            dateFormatter.dateStyle = .none
            dateFormatter.timeStyle = .short
            reminderDateString = dateFormatter.string(from: date)
        }

            let toDosList = SYCoreDataManager.sharedManager.fetchAllToDosToOneReminder(reminder: reminder)
                 cell.indexPath = indexPath
                 cell.showMoreDelegate = self
                 cell.initializeToDosCompactView(toDoList: toDosList ?? [],reminderTitleText: reminderTitle,reminderDateText: reminderDateString)
                 cell.changeTextViewStyle(isChecked: reminder.isCompleted)

           return cell
       }

    setupSnapshot(animated: true)
   }

Create a NSDiffableDataSourceSnapshot with the table view data

private func setupSnapshot(animated: Bool) {
    diffableDataSourceSnapshot = NSDiffableDataSourceSnapshot<Int, Reminder>()

    for (i , section) in (fetchedResultsController.sections?.enumerated())! {
        diffableDataSourceSnapshot.appendSections([i])
        let items = section.objects
        diffableDataSourceSnapshot.appendItems(items as! [Reminder])
        diffableDataSource?.apply(self.diffableDataSourceSnapshot, animatingDifferences: animated, completion: nil)
    }

}

NSFetchedResultsControllerDelegate for sections and rows

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

    switch type {
    case .insert:
        if let indexPath = newIndexPath {
            let section = fetchedResultsController.sections![indexPath.section]
            self.diffableDataSourceSnapshot.appendItems(section.objects as! [Reminder], toSection: indexPath.section)
            self.diffableDataSource?.apply(self.diffableDataSourceSnapshot, animatingDifferences: true)

        }
        break
    case .update:
        break
    case .delete:

        if let indexPath = indexPath {
            guard let item = self.diffableDataSource?.itemIdentifier(for: indexPath) else { return }
            self.diffableDataSourceSnapshot.deleteItems([item])
            self.diffableDataSource?.apply(self.diffableDataSourceSnapshot, animatingDifferences: true)
        }
        break
    case .move:
        if let indexPath = indexPath {
            guard let item = self.diffableDataSource?.itemIdentifier(for: indexPath) else { return }
            self.diffableDataSourceSnapshot.appendSections([indexPath.section])
            self.diffableDataSourceSnapshot.deleteItems([item])
            self.diffableDataSource?.apply(self.diffableDataSourceSnapshot, animatingDifferences: true)
        }
        if let newIndexPath = newIndexPath {
            let section = fetchedResultsController.sections![newIndexPath.section]

            // let items = fetchedResultsController.object(at: indexPath)
            print("snapppp" , diffableDataSourceSnapshot.sectionIdentifiers)
            let items = section.objects as! [Reminder]

            self.diffableDataSourceSnapshot.appendItems(items, toSection: newIndexPath.section)
            self.diffableDataSource?.apply(self.diffableDataSourceSnapshot, animatingDifferences: true)
        }
        break
    }
}

func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange sectionInfo: NSFetchedResultsSectionInfo, atSectionIndex sectionIndex: Int, for type: NSFetchedResultsChangeType) {
    switch type {
    case .insert:
        setupSnapshot(animated: false)
        break
    case .update:
        break
    case .delete:
        let section = self.diffableDataSourceSnapshot.sectionIdentifiers[sectionIndex]
        self.diffableDataSourceSnapshot.deleteSections([section])
                self.diffableDataSource?.apply(self.diffableDataSourceSnapshot, animatingDifferences: true)
        //setupSnapshot(animated: false)

        break
    case .move:
        break
    }
}

To work smoothly with Core Data the data source must be declared as
```
UITableViewDiffableDataSource<String,NSManagedObjectID>
```

In setupTableView rename the closure parameter labels with

(tableView, indexPath, objectID) -> UITableViewCell? in

and get the reminder with

let reminder = self.fetchedResultsController.object(at: indexPath)

let reminder = try! self.managedObjectContext.existingObject(with: objectID) as! Reminder

Then replace the entire methods

func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, 
     didChange anObject: Any, 
     at indexPath: IndexPath?, 
     for type: NSFetchedResultsChangeType, 
     newIndexPath: IndexPath?) { ... }

and

func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, 
     didChange sectionInfo: NSFetchedResultsSectionInfo, atSectionIndex sectionIndex: Int, 
     for type: NSFetchedResultsChangeType) { ... }

just with

func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChangeContentWith snapshot: NSDiffableDataSourceSnapshotReference) {       
    self.diffableDataSource.apply(snapshot as NSDiffableDataSourceSnapshot<String, NSManagedObjectID>, animatingDifferences: true)
}

Delete also the method setupSnapshot, it is not needed. After calling performFetch and on any change in the managed object context the framework creates the snapshot properly and calls the delegate method.

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