delete UITableViewCell with animation (error/crash) - ios

Question

I'd like to delete a UITableViewCell & a CoreData Object from a UITableView with an animation. I wrote this code for doing it:
func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
let mySelectedCell:UITableViewCell = tableView.cellForRowAtIndexPath(indexPath)!
//1
let appDelegate = UIApplication.sharedApplication().delegate as AppDelegate
let managedContext = appDelegate.managedObjectContext!
//2
let fetchRequest = NSFetchRequest(entityName:"Person")
//3
mySelectedCell.backgroundColor = green
mySelectedCell.detailTextLabel?.text = "Done"
mySelectedCell.accessoryType = UITableViewCellAccessoryType.Checkmark
let person = people[indexPath.row]
managedContext.deleteObject(person)
self.tableView.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Right)
}
I don't know why but the app is crashing if I select a cell, which I want to delete.
2015-03-29 18:00:10.776 MyApp[3001:79507] *** Assertion failure in -[UITableView _endCellAnimationsWithContext:], /SourceCache/UIKit_Sim/UIKit-3318.93/UITableView.m:1582
Crashing line: self.tableView.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Right)
Does someone knows what I've done wrong?
Update:
tableView.beginUpdates()
var numberItems:Int = people.count
self.tableView.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Right)
numberItems -= [indexPath].count // something like [indexPath].count
tableView.endUpdates()
func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
application.applicationIconBadgeNumber = people.count
return people.count
}
New error:
2015-03-29 19:14:15.972 MyApp[3389:89566] *** Assertion failure in -[UITableView _endCellAnimationsWithContext:], /SourceCache/UIKit_Sim/UIKit-3318.93/UITableView.m:1582
in this line of code: tableView.endUpdates()

Answer 1

If the table view displays Core Data objects using a fetched results controller then the only thing you have
to do to delete an object is to delete the object from the managed object context:
let context = self.fetchedResultsController.managedObjectContext
context.deleteObject(self.fetchedResultsController.objectAtIndexPath(indexPath) as NSManagedObject)
and of course save the context to make the change permanent.
Updating the table view is then done "automatically" by the
fetched results controller delegate methods
func controllerWillChangeContent(controller: NSFetchedResultsController)
func controller(controller: NSFetchedResultsController, didChangeSection sectionInfo: NSFetchedResultsSectionInfo, atIndex sectionIndex: Int, forChangeType type: NSFetchedResultsChangeType)
func controller(controller: NSFetchedResultsController, didChangeObject anObject: AnyObject, atIndexPath indexPath: NSIndexPath?, forChangeType type: NSFetchedResultsChangeType, newIndexPath: NSIndexPath?)
func controllerDidChangeContent(controller: NSFetchedResultsController)
You'll find a typical implementation of these methods in the
NSFetchedResultsControllerDelegate documentation, if you haven't
implemented them already.
Also you should not have a "copy" of the fetched objects in your
people array. The fetched results controller is directly used
in the table view data source methods, for example:
override func numberOfSectionsInTableView(tableView: UITableView) -> Int {
return self.fetchedResultsController.sections?.count ?? 0
}
override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
let sectionInfo = self.fetchedResultsController.sections![section] as NSFetchedResultsSectionInfo
return sectionInfo.numberOfObjects
}
override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
let cell = tableView.dequeueReusableCellWithIdentifier("Cell", forIndexPath: indexPath) as UITableViewCell
self.configureCell(cell, atIndexPath: indexPath)
return cell
}
If you create a fresh "Master-Detail + Core Data Application" in Xcode
then you'll get all the necessary template code that you need.

Answer 2

You have to put yout method deleteRowsAtIndexPaths inside this two methods in the following way :
var path = [NSIndexPath]()
// This is only a example with the index [0..numberOfItemsToDelete-1]
for (var i = 0; i < numberOfItemsToDelete; i++) {
path.append(NSIndexPath(forRow: i, inSection: 0))
}
tableView.beginUpdates()
self.tableView.deleteRowsAtIndexPaths(path, withRowAnimation: .Right)
self.numberOfItems -= theNumberYouDeletedAbove // something like [indexPath].count
tableView.endUpdates()
And of course you have to update the numberOfRowsInSection method because it will throw a run-time error , you can do something like this :
override func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
return numberOfItems
}
Where numberOfItems match the size of the array you use to display the items.
I hope this help you.

Answer 3

FIRST, remove this line which try to duplicate and involve managedContext job an cause crash.
self.tableView.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Right)
SECOND, Now you should able to delete without crash and without animation.
THIRD, Let the NSFetchedResultsController delete and trigger animation in its way with "didChange" handler.
func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>,
didChange anObject: Any,
at indexPath: IndexPath?,
for type: NSFetchedResultsChangeType,
newIndexPath: IndexPath?)
{
print(indexPath)
if type == .delete{
tableView.deleteRows(at: [indexPath!], with: .automatic)
}
}
func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
tableView.endUpdates()
//0.4 sec delay before refreshing the table
DispatchQueue.main.asyncAfter(wallDeadline: .now() + 0.4) {
self.refresh()
}
}
func refresh(){
tableView.reloadData()
}
If you can not delete at SECOND step;
Check, if you've implemented:
NSFetchedResultsControllerDelegate
in the class definition and set the delegate in the class also e.g.
yourResultsController.delegate = self