drag and drop collectionViewCell in swift - ios

Question

whenever I drag and drop the cell in other section app gets crashed and when I drag and drop the cell in same section it works good any ideas how to fix it thank a lot in advance. below is the full code.
// error : Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'attempt to insert item 21 into section 1, but there are only 1 sections after the update'
// ViewController
import UIKit
class ViewController: UIViewController {
var deviceName = ""
let cellName = "IconCell". // cell name
var pressActivated = false
#IBOutlet weak var collectionView: UICollectionView!
var nameArrays = [
0: ["twitter", "facebook", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", "", ""],
1: ["twitter", "twitter", "", "twitter", "", "", "", "", "", "", "", "twitter", "", "", "twitter", "twitter", "twitter", "twitter", "twitter", "twitter", "twitter", "twitter", "twitter", "twitter"]
]
let statusBarTappedNotification = Notification(name: Notification.Name(rawValue: "statusBarTappedNotification"))
#IBOutlet weak var pageController: UIPageControl!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
setupView()
}
private func setupView(){
self.collectionView.register(UINib.init(nibName: cellName, bundle: nil), forCellWithReuseIdentifier: cellName)
pageController.numberOfPages = nameArrays.keys.count
pageController.currentPage = 0
collectionView.dragDelegate = self
collectionView.dropDelegate = self
// collectionView.dragInteractionEnabled = true
collectionView.reorderingCadence = .fast
NotificationCenter.default.addObserver(forName: statusBarTappedNotification.name, object: .none, queue: .none) { _ in
print("status bar tapped")
self.pressActivated = false
self.collectionView.reloadData()
}
}
#objc private func longPress(){
print("long Pressed")
pressActivated = true
if pressActivated{
collectionView.dragInteractionEnabled = true
}
collectionView.reloadData()
}
private func copyItems(coordinator: UICollectionViewDropCoordinator, destinationIndexPath: IndexPath, collectionView: UICollectionView)
{
collectionView.performBatchUpdates({
var indexPaths = [IndexPath]()
for (index, item) in coordinator.items.enumerated()
{
let indexPath = IndexPath(row: destinationIndexPath.item + index, section: destinationIndexPath.section)
print(indexPath.section)
print(indexPath.item)
let key = self.nameArrays.keys.sorted()[indexPath.section]
self.nameArrays[key]!.insert(item.dragItem.localObject as! String, at: indexPath.item)
//
indexPaths.append(indexPath)
}
collectionView.insertItems(at: indexPaths)
})
}
private func reorderItems(coordinator: UICollectionViewDropCoordinator, destinationIndexPath: IndexPath, collectionView: UICollectionView)
{
let items = coordinator.items
if items.count == 1, let item = items.first, let sourceIndexPath = item.sourceIndexPath
{
var dIndexPath = destinationIndexPath
if dIndexPath.row >= collectionView.numberOfItems(inSection: 0)
{
dIndexPath.row = collectionView.numberOfItems(inSection: 0) - 1
}
collectionView.performBatchUpdates({
self.nameArrays.removeValue(forKey: sourceIndexPath.item)
collectionView.deleteItems(at: [sourceIndexPath])
collectionView.insertItems(at: [dIndexPath])
print(dIndexPath) // till here it works good
})
coordinator.drop(items.first!.dragItem, toItemAt: dIndexPath)
}
}
}
extension ViewController: UICollectionViewDelegate,UICollectionViewDataSource,UICollectionViewDelegateFlowLayout {
func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
for cell in collectionView.visibleCells {
let indexPath = collectionView.indexPath(for: cell)
if let indexPath = indexPath {
print("\(indexPath)")
self.pageController.currentPage = indexPath.section
}
}
}
func numberOfSections(in collectionView: UICollectionView) -> Int {
return nameArrays.keys.count. // number of sections in collection view
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
let key = nameArrays.keys.sorted()[section]
return nameArrays[key]!.count // number of rows in collection View
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell: IconCell = collectionView.dequeueReusableCell(withReuseIdentifier: cellName, for: indexPath) as! IconCell
// setting data to cells
let holdGesture = UILongPressGestureRecognizer()
holdGesture.addTarget(self, action: #selector(longPress))
holdGesture.minimumPressDuration = 0.5
cell.addGestureRecognizer(holdGesture)
cell.backgroundColor = .clear
let key = nameArrays.keys.sorted()[indexPath.section]
cell.appName.text = nameArrays[key]![indexPath.item]
cell.appIcon.image = UIImage.init(named: nameArrays[key]![indexPath.item])
if pressActivated{
let transformAnim = CAKeyframeAnimation(keyPath:"transform")
transformAnim.values = [NSValue(caTransform3D: CATransform3DMakeRotation(0.04, 0.0, 0.0, 1.0)),NSValue(caTransform3D: CATransform3DMakeRotation(-0.04 , 0, 0, 1))]
transformAnim.autoreverses = true
transformAnim.duration = Double(indexPath.row).truncatingRemainder(dividingBy: 2) == 0 ? 0.115 : 0.105
transformAnim.repeatCount = Float.infinity
cell.layer.add(transformAnim, forKey: "transform")
cell.closeButton.isHidden = false
if cell.appName.text == ""{
cell.closeButton.isHidden = true
}
}
else {
cell.closeButton.isHidden = true
}
return cell
}
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
return CGSize(width: collectionView.bounds.width/4 - 10, height: 80)
}
}
class CustomCollectionViewFlowLayout: UICollectionViewFlowLayout
{
override func targetContentOffset(forProposedContentOffset proposedContentOffset: CGPoint, withScrollingVelocity velocity: CGPoint) -> CGPoint
{
if let collectionViewBounds = self.collectionView?.bounds
{
let halfWidthOfVC = collectionViewBounds.size.width * 0.5
let proposedContentOffsetCenterX = proposedContentOffset.x + halfWidthOfVC
if let attributesForVisibleCells = self.layoutAttributesForElements(in: collectionViewBounds)
{
var candidateAttribute : UICollectionViewLayoutAttributes?
for attributes in attributesForVisibleCells
{
let candAttr : UICollectionViewLayoutAttributes? = candidateAttribute
if candAttr != nil
{
let a = attributes.center.x - proposedContentOffsetCenterX
let b = candAttr!.center.x - proposedContentOffsetCenterX
if abs(a) < abs(b)
{
candidateAttribute = attributes
}
}
else
{
candidateAttribute = attributes
continue
}
}
if candidateAttribute != nil
{
return CGPoint(x: candidateAttribute!.center.x - halfWidthOfVC, y: proposedContentOffset.y);
}
}
}
return CGPoint.zero
}
}
extension ViewController : UICollectionViewDragDelegate
{
func collectionView(_ collectionView: UICollectionView, itemsForBeginning session: UIDragSession, at indexPath: IndexPath) -> [UIDragItem]
{
let key = nameArrays.keys.sorted()[indexPath.section]
let item = self.nameArrays[key]![indexPath.item]
let itemProvider = NSItemProvider(object: item as NSString)
let dragItem = UIDragItem(itemProvider: itemProvider)
dragItem.localObject = item
return [dragItem]
}
func collectionView(_ collectionView: UICollectionView, itemsForAddingTo session: UIDragSession, at indexPath: IndexPath, point: CGPoint) -> [UIDragItem]
{
let key = nameArrays.keys.sorted()[indexPath.section]
let item = self.nameArrays[key]![indexPath.item]
let itemProvider = NSItemProvider(object: item as NSString)
let dragItem = UIDragItem(itemProvider: itemProvider)
dragItem.localObject = item
return [dragItem]
}
func collectionView(_ collectionView: UICollectionView, dragPreviewParametersForItemAt indexPath: IndexPath) -> UIDragPreviewParameters?
{
let previewParameters = UIDragPreviewParameters()
previewParameters.visiblePath = UIBezierPath(rect: CGRect(x: 25, y: 25, width: 120, height: 120))
return previewParameters
}
}
// MARK: - UICollectionViewDropDelegate Methods
extension ViewController : UICollectionViewDropDelegate
{
func collectionView(_ collectionView: UICollectionView, canHandle session: UIDropSession) -> Bool
{
return session.canLoadObjects(ofClass: NSString.self)
}
func collectionView(_ collectionView: UICollectionView, dropSessionDidUpdate session: UIDropSession, withDestinationIndexPath destinationIndexPath: IndexPath?) -> UICollectionViewDropProposal
{
if collectionView.hasActiveDrag
{
return UICollectionViewDropProposal(operation: .move, intent: .insertAtDestinationIndexPath)
}
else
{
return UICollectionViewDropProposal(operation: .forbidden)
}
}
func collectionView(_ collectionView: UICollectionView, performDropWith coordinator: UICollectionViewDropCoordinator)
{
let destinationIndexPath: IndexPath
if let indexPath = coordinator.destinationIndexPath
{
destinationIndexPath = indexPath
}
else
{
// Get last index path of table view.
let section = collectionView.numberOfSections - 1
let row = collectionView.numberOfItems(inSection: section)
destinationIndexPath = IndexPath(row: row, section: section)
}
switch coordinator.proposal.operation
{
case .move:
print("move")
self.reorderItems(coordinator: coordinator, destinationIndexPath:destinationIndexPath, collectionView: collectionView)
break
case .copy:
print("copy")
self.copyItems(coordinator: coordinator, destinationIndexPath: destinationIndexPath, collectionView: collectionView)
default:
return
}
}
}

Answer 1

you must use beginInteractiveMovementForItemAtIndexPath:
and endInteractiveMovement
see Reordering Items Interactively section in UICollectionView reference