App crashes after updating CoreData model that is being displayed in a UITableView

Question

I have a strange bug that is extremely rare but causes the app to crash. I can\'t reproduce it but I finally found a crash report documenting this. (I posted the stack trac

Answer 1

indexPath is the index BEFORE the deletes and inserts are applied; newIndexPath is the index AFTER the deletes and inserts are applied.

For updates you don't care where it was BEFORE the inserts and delete - only after - so use newIndexPath not indexPath. This will fix crashes that can happen when you an update and insert (or update and delete) at the same time.

For move the delegate is saying where it moved from BEFORE the inserts and where it should be inserted AFTER the inserts and deletes. This can be challenging when you have a move and insert (or move and delete). I fixed this by saving all the changes from controller:didChangeObject:atIndexPath:forChangeType:newIndexPath: into three different indexPath arrays: insert, delete and update. When you get a move add an entry for it in both the insert array and in the delete array. In controllerDidChangeContent: sort the delete array descending and the insert array ascending. Then apply the changes - first delete, then insert, then update. This will fix crashes that can happens when you have a move and insert (or move and delete) at the same time.

It is the same principle for sections. Save the sections changes in arrays, and then apply the changes in order: deletes (descending), sectionDelete (descending), sectionInserts (ascending), inserts(ascending), updates (any order). Sections can't move or be updated.