如何在Swift 2.0中滑动删除核心数据表视图

Question

I have a table view within a VC. It is populated from a core data object using the following code:

// Variables
var allFruits: NSArray
var managedObjectContext: NSManagedObjectContext
let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate

func loadFruits(){
    // Try to load all of the Fruits from the core data.
    let fetchRequest = NSFetchRequest()

    let entityDescription = NSEntityDescription.entityForName("Fruit", inManagedObjectContext: self.managedObjectContext)

    fetchRequest.entity = entityDescription
    do{
        self.allFruits = try self.managedObjectContext.executeFetchRequest(fetchRequest)

        if self.allFruits.count == 0{
            print("No saved Fruits")
        }
    }
    catch
    {
        let fetchError = error as NSError
        print(fetchError)
    }
}   

Then the table view is populated with this specific fruit data. I have got this method for deletion of the Fruits from the table

func tableView(tableView: UITableView, commitEditingStyle editingStyle: UITableViewCellEditingStyle, forRowAtIndexPath indexPath: NSIndexPath) {
    if (editingStyle == UITableViewCellEditingStyle.Delete) {
         // handle delete (by removing the data from your array and updating the tableview)
         managedObjectContext.deleteObject(allFruits[indexPath.row] as! NSManagedObject)

         // Attempt to save the object
         do{
             try appDelegate.managedObjectContext.save()
         }
             catch let error{
             print("Could not save Deletion \(error)")
         }

         // Remove the deleted item from the table view
         self.tableView.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Fade)

         // Reload the fruits
         self.loadFruits()

         // Reload the table view
         tableView.reloadData()
    }
}

This instead just crashes the app every time I try to delete the Fruits.

'NSInternalInconsistencyException', reason: 'Invalid update: invalid number of rows in section 0. The number of rows contained in an existing section after the update (5) must be equal to the number of rows contained in that section before the update (5), plus or minus the number of rows inserted or deleted from that section (0 inserted, 1 deleted) and plus or minus the number of rows moved into or out of that section (0 moved in, 0 moved out).'

I am suspecting that there is some issue with the fact that I am using an NSArray as opposed to an NSMutableArray .

How can I fix this issue?

Thanks in advance.

Answer 1

First of all use a Swift array rather than a Foundation array

var allFruits = [NSManagedObject]()

This avoids a lot of type casting.

To keep Core Data and the table view in sync you have to delete the object in Core Data and in the model. The solution to completely reload both the model and the view is very expensive and not needed at all.

func tableView(tableView: UITableView, commitEditingStyle editingStyle: UITableViewCellEditingStyle, forRowAtIndexPath indexPath: NSIndexPath) {
  if editingStyle == .Delete {

    let objectToDelete = allFruits[indexPath.row]
    allFruits.removeAtIndex(indexPath.row)
    managedObjectContext.deleteObject(objectToDelete)

    //Attempt to save the object
    do{
      try appDelegate.managedObjectContext.save()
      tableView.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Fade)
    }
    catch let error{
      print("Could not save Deletion \(error)")
    }
  }
}

deleteRowsAtIndexPaths includes updating the UI so reloading the table view is not needed.

If the model of the table view is NSManagedObject it's recommended to use NSFetchedResultsController

Answer 2

You should update data source before delete. Like this:

     //Reload the fruits
     self.loadFruits()

     //Remove the deleted item from the table view
     self.tableView.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Fade)

And if you're sure there's no other changes,it's no need to reload data because this costs a lot.

Answer 3

I fixed my code by simply changing this method:

func tableView(tableView: UITableView, commitEditingStyle editingStyle: UITableViewCellEditingStyle, forRowAtIndexPath indexPath: NSIndexPath) {
        if (editingStyle == UITableViewCellEditingStyle.Delete) {


             // handle delete (by removing the data from your array and updating the tableview)
             managedObjectContext.deleteObject(allFruits[indexPath.row] as! NSManagedObject)

             //Attempt to save the object
             do{
             try appDelegate.managedObjectContext.save()
             }
             catch let error{
             print("Could not save Deletion \(error)")
             }

             //Reload the fruits
             self.loadFruits()

             //Reload the table view
             tableView.reloadData()


        }
    }

This successfully deletes the object from the core data as well as updating the table view.

Answer 4

Updated for Swift 3 Xcode 8 iOS 10

The following code snippet adds a 'swipe to delete' to your Table Row, and also saves the changes to CoreData.

override func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCellEditingStyle, forRowAt indexPath: IndexPath) {
    let context = (UIApplication.shared.delegate as! AppDelegate).persistentContainer.viewContext

    if editingStyle == .delete {
         context.delete(tasks[indexPath.row] as NSManagedObject)
        //objects.remove(at: indexPath.row)
        tableView.deleteRows(at: [indexPath], with: .fade)

        //Save the object
        do{
            try (UIApplication.shared.delegate as! AppDelegate).saveContext()
        }
        catch let error{
            print("Cannot Save: Reason: \(error)")
        }

        //Reload your Table Data
        getData()

        //Reload the table view
        tableView.reloadData()

    } else if editingStyle == .insert {
        // Create a new instance of the appropriate class, insert it into the array, and add a new row to the table view.
    }
}