Swift: Drag and drop cells within the same UICollectionViewController

Question

I am building an app which enables user to drag a UIView onto another. Currently I have the implementation as a UIScrollView but that does not give me the best experience as to achieve an experience like Apple's drag and drop requires handling of many cases ( including edge cases).

I am curious if this can be done using a UICollectionView. I am looking to drag cells onto another cells after which the cells contents merge and the source cell is removed.

Any idea/ suggestion would be appreciated. I am not sure if adding what I have is neccessary but if needed I can certainly add the code which I have.

Answer 1

Yes it's possible with UICollectionView.

Assign below delegates to UICollectionView:

UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout, UICollectionViewDragDelegate, UICollectionViewDropDelegate 

Write below DataSource methods:

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return YourDataSource.count
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: PDFViewCollectionViewCell.reuseIdentifier, for: indexPath) as! PDFViewCollectionViewCell
        return cell
    }

then write delegate methods for dragging:

func collectionView(_ collectionView: UICollectionView, itemsForBeginning session: UIDragSession, at indexPath: IndexPath) -> [UIDragItem] {
        let item = "\(indexPath.item)"
        let itemProvider = NSItemProvider(object: NSString(string: "\(indexPath.item)"))
        let dragItem = UIDragItem(itemProvider: itemProvider)
        dragItem.localObject = item
        print("DRAG ITEM IN BEGIN: \(item)")
        return [dragItem]
    }

 func collectionView(_ collectionView: UICollectionView, performDropWith coordinator: UICollectionViewDropCoordinator) {
        let destinationIndexPath: IndexPath

        if let indexPath = coordinator.destinationIndexPath {
            destinationIndexPath = indexPath
        } else {
            let section = collectionView.numberOfSections - 1
            let row = collectionView.numberOfItems(inSection: section)
            destinationIndexPath = IndexPath(row: row, section: section)
        }


        if let item = coordinator.items.first,
           let sourceIndexPath = item.sourceIndexPath {
            collectionView.performBatchUpdates {
                let objNeedToInsert = YourDataSource[Int(item.dragItem.localObject as! String)!]
                self.YourDataSource.remove(at: sourceIndexPath.item)
                self.YourDataSource.insert(objNeedToInsert, at: destinationIndexPath.item)
                collectionView.deleteItems(at: [sourceIndexPath])
                collectionView.insertItems(at: [destinationIndexPath])

            }
            coordinator.drop(item.dragItem, toItemAt: destinationIndexPath)
        }
}

func collectionView(_ collectionView: UICollectionView, dropSessionDidUpdate session: UIDropSession, withDestinationIndexPath destinationIndexPath: IndexPath?) -> UICollectionViewDropProposal {
        if collectionView.hasActiveDrag {
            return UICollectionViewDropProposal(operation: .move, intent: .insertAtDestinationIndexPath)
        }
        return UICollectionViewDropProposal(operation: .forbidden)
    }

Best of Luck... Happy Coding :)