Collection Update

About —[email protected] —https://github.com/onmyway133 —https://github.com/hyperoslo

Content —TableView / CollectionView —Drag and Drop —Let's play some games ! —Diff

NSCollectionView !

Newsloop

Drag and Drop Demo !

index vs offset Array(0..<10).enumerated().forEach { (offset, element) in } - https://en.wikipedia.org/wiki/Zero-based_numbering - offset from the starting position

NSInternalInconsistencyException Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Invalid update: invalid number of items in section 0. The number of items contained in an existing section after the update (213) must be equal to the number of items contained in that section before the update (154), plus or minus the number of items inserted or deleted from that section (40 inserted, 0 deleted) and plus or minus the number of items moved into or out of that section (0 moved in, 0 moved out).'

Game of IndexPath —https://github.com/onmyway133/ CollectionUpdateExample —10 quizzes items = ["a", "b", "c", "d", "e", "f"]

1) insert 3 items at the end items.append(contentsOf: ["g", "h", "i"]) // a, b, c, d, e, f, g, h, i let indexPaths = Array(6...8).map { IndexPath(item: $0, section: 0) } collectionView.insertItems(at: indexPaths)

2) delete 3 items at the end items.removeLast() items.removeLast() items.removeLast() // a, b, c let indexPaths = Array(3...5).map { IndexPath(item: $0, section: 0) } collectionView.deleteItems(at: indexPaths)

3) update item at index 2 items[2] = " ! " // a, b, ! , d, e, f let indexPath = IndexPath(item: 2, section: 0) collectionView.reloadItems(at: [indexPath])

4) move item "c" to the end items.remove(at: 2) items.append("c") // a, b, d, e, f, c collectionView.moveItem( at: IndexPath(item: 2, section: 0), to: IndexPath(item: 5, section :0) )

5) delete 3 items at the beginning, then insert 3 items at the end items.removeFirst() items.removeFirst() items.removeFirst() items.append(contentsOf: ["g", "h", "i"]) // d, e, f, g, h, i collectionView.performBatchUpdates({ let deleteIndexPaths = Array(0...2).map { IndexPath(item: $0, section: 0) } collectionView.deleteItems(at: deleteIndexPaths) let insertIndexPaths = Array(3...5).map { IndexPath(item: $0, section: 0) } collectionView.insertItems(at: insertIndexPaths) }, completion: nil)

6) insert 3 items at the end, then delete 3 items beginning items.append(contentsOf: ["g", "h", "i"]) items.removeFirst() items.removeFirst() items.removeFirst() // d, e, f, g, h, i collectionView.performBatchUpdates({ let insertIndexPaths = Array(6...8).map { IndexPath(item: $0, section: 0) } collectionView.insertItems(at: insertIndexPaths) let deleteIndexPaths = Array(0...2).map { IndexPath(item: $0, section: 0) } collectionView.deleteItems(at: deleteIndexPaths) }, completion: nil)

! Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'attempt to insert item 6 into section 0, but there are only 6 items in section 0 after the update'

performBatchUpdates Deletes are processed before inserts in batch operations

6) insert 3 items at the end, then delete 3 items beginning ! items.append(contentsOf: ["g", "h", "i"]) items.removeFirst() items.removeFirst() items.removeFirst() // d, e, f, g, h, i collectionView.performBatchUpdates({ let deleteIndexPaths = Array(0...2).map { IndexPath(item: $0, section: 0) } collectionView.deleteItems(at: deleteIndexPaths) let insertIndexPaths = Array(3...5).map { IndexPath(item: $0, section: 0) } collectionView.insertItems(at: insertIndexPaths) }, completion: nil)

Operations insertItems(at indexPaths: [IndexPath]) deleteItems(at indexPaths: [IndexPath]) reloadItems(at indexPaths: [IndexPath]) moveItem(at indexPath: IndexPath, to newIndexPath: IndexPath) performBatchUpdates(_ updates, completion) insertSections(_ sections: IndexSet) deleteSections(_ sections: IndexSet) reloadSections(_ sections: IndexSet) moveSection(_ section: Int, toSection newSection: Int)

Ordering of Operations and Index Paths —https://developer.apple.com/library/content/ documentation/UserExperience/Conceptual/ TableView_iPhone/ManageInsertDeleteRow/ ManageInsertDeleteRow.html

Wagner–Fischer algorithm —https://en.wikipedia.org/wiki/ Wagner%E2%80%93Fischer_algorithm —https://en.wikipedia.org/wiki/ Dynamic_programming Computes the edit distance between two strings of characters.

"kit" -> "kat"

Deletions "k" -> "" ! 1 deletion "ki" -> "" ! 2 deletions "kit" -> "" ! 3 deletions

Insertions "" -> "k" ! 1 insertion "" -> "ka" ! 2 insertions "" -> "kat" ! 3 insertions

If equal, take value from the top left

horizonally: insertion vertically: deletion diagonally: substitution If not equal, check minimum value from left, top, top left. Then increase by one

"k" -> "kat" ! 2 insertions

It equals again, take value from top left. Bottom right value gives edit distance (number of steps) "kit" -> "kat" ! Substitute "i" with "a"

insertions: insertItems deletions: deleteItems substitutions: reloadItems move: deletion + insertion moveItem

Edit steps —delete, insert, move, substitute —https://github.com/onmyway133/DeepDiff

Complexity —O(mn) —10k items ! Performance —Collection size —Equatable —Hashable

Alternatives —Heckel http://documents.scribd.com/docs/ 10ro9oowpo1h81pgh1as.pdf —Wu https://publications.mpi-cbg.de/ Wu19906334.pdf —Myers http://www.xmailserver.org/diff2.pdf

Q & A Thanks for listening. Hope you have a great time