DragDrop7.swift

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.items.remove(at: sourceIndexPath.row)
        self.items.insert(item.dragItem.localObject as! String, at: dIndexPath.row)
        collectionView.deleteItems(at: [sourceIndexPath])
        collectionView.insertItems(at: [dIndexPath])
    })
    coordinator.drop(item.dragItem, toItemAt: dIndexPath)
}