Drag and reorder - UICollectionview with sections

Question

Is that possible to do drag and reorder from one section to another section from collectionview - iOS 9.

Every time am dragging from 1st section to drop at 4th secti

Answer 1

Details

• Xcode 10.2 (10E125), Swift 5

Links

Coding for iOS 11: How to drag & drop into collections & tables

Full Sample

ViewController

import UIKit

enum CellModel {
    case simple(text: String)
    case availableToDrop
}

class ViewController: UIViewController {

    private lazy var cellIdentifier = "cellIdentifier"
    private lazy var supplementaryViewIdentifier = "supplementaryViewIdentifier"
    private lazy var sections = 10
    private lazy var itemsInSection = 2
    private lazy var numberOfElementsInRow = 3

    private lazy var data: [[CellModel]] = {
        var count = 0
        return (0 ..< sections).map { _ in
            return (0 ..< itemsInSection).map { _ -> CellModel in
                count += 1
                return .simple(text: "cell \(count)")
            }
        }
    }()

    override func viewDidLoad() {
        super.viewDidLoad()

        let collectionViewFlowLayout = UICollectionViewFlowLayout()
        collectionViewFlowLayout.minimumLineSpacing = 5
        collectionViewFlowLayout.minimumInteritemSpacing = 5
        let _numberOfElementsInRow = CGFloat(numberOfElementsInRow)
        let allWidthBetwenCells = _numberOfElementsInRow == 0 ? 0 : collectionViewFlowLayout.minimumInteritemSpacing*(_numberOfElementsInRow-1)
        let width = (view.frame.width - allWidthBetwenCells)/_numberOfElementsInRow
        collectionViewFlowLayout.itemSize = CGSize(width: width, height: width)
        collectionViewFlowLayout.headerReferenceSize = CGSize(width: 0, height: 40)

        let collectionView = UICollectionView(frame: .zero, collectionViewLayout: collectionViewFlowLayout)
        collectionView.backgroundColor = .white
        view.addSubview(collectionView)
        collectionView.translatesAutoresizingMaskIntoConstraints = false
        collectionView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor).isActive = true
        collectionView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor).isActive = true
        collectionView.leftAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leftAnchor).isActive = true
        collectionView.rightAnchor.constraint(equalTo: view.safeAreaLayoutGuide.rightAnchor).isActive = true

        collectionView.register(CollectionViewCell.self, forCellWithReuseIdentifier: cellIdentifier)
        collectionView.register(SupplementaryView.self,
                                forSupplementaryViewOfKind: UICollectionView.elementKindSectionHeader,
                                withReuseIdentifier: supplementaryViewIdentifier)

        collectionView.dragInteractionEnabled = true
        collectionView.reorderingCadence = .fast
        collectionView.dropDelegate = self
        collectionView.dragDelegate = self

        collectionView.delegate = self
        collectionView.dataSource = self
    }
}

extension ViewController: UICollectionViewDelegate { }
extension ViewController: UICollectionViewDataSource {

    func numberOfSections(in collectionView: UICollectionView) -> Int { return data.count }
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return data[section].count
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        switch data[indexPath.section][indexPath.item] {
            case .simple(let text):
                let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellIdentifier, for: indexPath) as! CollectionViewCell
                cell.label?.text = text
                cell.backgroundColor = .gray
                return cell
            case .availableToDrop:
                let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellIdentifier, for: indexPath) as! CollectionViewCell
                cell.backgroundColor = UIColor.green.withAlphaComponent(0.3)
                return cell
        }
    }

    func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
        let headerView = collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: supplementaryViewIdentifier, for: indexPath as IndexPath) as! SupplementaryView
        return headerView
    }
}

extension ViewController: UICollectionViewDragDelegate {

    func collectionView(_ collectionView: UICollectionView, itemsForBeginning session: UIDragSession, at indexPath: IndexPath) -> [UIDragItem] {
        let itemProvider = NSItemProvider(object: "\(indexPath)" as NSString)
        let dragItem = UIDragItem(itemProvider: itemProvider)
        dragItem.localObject = data[indexPath.section][indexPath.row]
        return [dragItem]
    }

    func collectionView(_ collectionView: UICollectionView, itemsForAddingTo session: UIDragSession, at indexPath: IndexPath, point: CGPoint) -> [UIDragItem] {
        let itemProvider = NSItemProvider(object: "\(indexPath)" as NSString)
        let dragItem = UIDragItem(itemProvider: itemProvider)
        dragItem.localObject = data[indexPath.section][indexPath.row]
        return [dragItem]
    }


    func collectionView(_ collectionView: UICollectionView, dragSessionWillBegin session: UIDragSession) {
        var itemsToInsert = [IndexPath]()
        (0 ..< data.count).forEach {
            itemsToInsert.append(IndexPath(item: data[$0].count, section: $0))
            data[$0].append(.availableToDrop)
        }
        collectionView.insertItems(at: itemsToInsert)
    }

    func collectionView(_ collectionView: UICollectionView, dragSessionDidEnd session: UIDragSession) {
        var removeItems = [IndexPath]()
        for section in 0..<data.count {
            for item in  0..<data[section].count {
                switch data[section][item] {
                    case .availableToDrop: removeItems.append(IndexPath(item: item, section: section))
                    case .simple: break
                }
            }
        }
        removeItems.forEach { data[$0.section].remove(at: $0.item) }
        collectionView.deleteItems(at: removeItems)
    }
}

extension ViewController: UICollectionViewDropDelegate {
    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)
        }

        switch coordinator.proposal.operation {
            case .move:
                reorderItems(coordinator: coordinator, destinationIndexPath:destinationIndexPath, collectionView: collectionView)
            case .copy:
                copyItems(coordinator: coordinator, destinationIndexPath: destinationIndexPath, collectionView: collectionView)
            default: return
        }
    }

    func collectionView(_ collectionView: UICollectionView, canHandle session: UIDropSession) -> Bool { return true }
    func collectionView(_ collectionView: UICollectionView, dropSessionDidUpdate session: UIDropSession, withDestinationIndexPath destinationIndexPath: IndexPath?) -> UICollectionViewDropProposal {
        if collectionView.hasActiveDrag, let destinationIndexPath = destinationIndexPath {
            switch data[destinationIndexPath.section][destinationIndexPath.row] {
                case .simple:
                    return UICollectionViewDropProposal(operation: .move, intent: .insertAtDestinationIndexPath)
                case .availableToDrop:
                    return UICollectionViewDropProposal(operation: .move, intent: .insertIntoDestinationIndexPath)
            }
        } else { return UICollectionViewDropProposal(operation: .forbidden) }
    }

    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,
            let localObject = item.dragItem.localObject as? CellModel {

            collectionView.performBatchUpdates ({
                data[sourceIndexPath.section].remove(at: sourceIndexPath.item)
                data[destinationIndexPath.section].insert(localObject, at: destinationIndexPath.item)
                collectionView.deleteItems(at: [sourceIndexPath])
                collectionView.insertItems(at: [destinationIndexPath])
            })
        }
    }

    private func copyItems(coordinator: UICollectionViewDropCoordinator, destinationIndexPath: IndexPath, collectionView: UICollectionView) {
        collectionView.performBatchUpdates({
            var indexPaths = [IndexPath]()
            for (index, item) in coordinator.items.enumerated() {
                if let localObject = item.dragItem.localObject as? CellModel {
                    let indexPath = IndexPath(row: destinationIndexPath.row + index, section: destinationIndexPath.section)
                    data[indexPath.section].insert(localObject, at: indexPath.row)
                    indexPaths.append(indexPath)
                }
            }
            collectionView.insertItems(at: indexPaths)
        })
    }
}

Cells

import UIKit

class CollectionViewCell: UICollectionViewCell {
    weak var label: UILabel?

    override init(frame: CGRect) {
        super.init(frame: frame)
        clipsToBounds = true
        let label = UILabel(frame: .zero)
        label.contentMode = .scaleAspectFill
        addSubview(label)
        label.translatesAutoresizingMaskIntoConstraints = false
        label.topAnchor.constraint(equalTo: topAnchor).isActive = true
        label.bottomAnchor.constraint(equalTo: bottomAnchor).isActive = true
        label.leftAnchor.constraint(equalTo: leftAnchor).isActive = true
        label.rightAnchor.constraint(equalTo: rightAnchor).isActive = true
        label.textAlignment = .center
        label.textColor = .white
        self.label = label
        layer.borderWidth = 1
        layer.borderColor = UIColor.white.cgColor
        backgroundColor = .white
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }

    override func prepareForReuse() {
        super.prepareForReuse()
        label?.text = nil
        backgroundColor = .white
    }
}

import UIKit

class SupplementaryView: UICollectionReusableView {

    weak var label: UILabel?
    override init(frame: CGRect) {
        super.init(frame: frame)
        backgroundColor = UIColor.blue.withAlphaComponent(0.7)
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }
}

Result

Answer 2

The idea of @Vasily Bodnarchuk is brilliant,

to move item to the end of each section, by adding an item when dragging

Code Optimization to @Vasily Bodnarchuk's solution.

Use

func collectionView(_ collectionView: UICollectionView, performDropWith coordinator: UICollectionViewDropCoordinator) {
        if let destinationIndexPath = coordinator.destinationIndexPath, case UIDropOperation.move = coordinator.proposal.operation{
            reorderItems(coordinator: coordinator, destinationIndexPath:destinationIndexPath, collectionView: collectionView)
        }
    }

instead of

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)
        }

        switch coordinator.proposal.operation {
            case .move:
                reorderItems(coordinator: coordinator, destinationIndexPath:destinationIndexPath, collectionView: collectionView)
            case .copy:
                copyItems(coordinator: coordinator, destinationIndexPath: destinationIndexPath, collectionView: collectionView)
            default: return
        }
    }

The else won't happen.

because of the forbidden situation

No destinationIndexPath , then forbidden

func collectionView(_ collectionView: UICollectionView, dropSessionDidUpdate session: UIDropSession, withDestinationIndexPath destinationIndexPath: IndexPath?) -> UICollectionViewDropProposal {
        if collectionView.hasActiveDrag, let destinationIndexPath = destinationIndexPath {
            switch data[destinationIndexPath.section][destinationIndexPath.row] {
                case .simple:
                    return UICollectionViewDropProposal(operation: .move, intent: .insertAtDestinationIndexPath)
                case .availableToDrop:
                    return UICollectionViewDropProposal(operation: .move, intent: .insertIntoDestinationIndexPath)
            }
        } else { return UICollectionViewDropProposal(operation: .forbidden) }
    }

---

And in the solution scene:

private func copyItems(coordinator: UICollectionViewDropCoordinator, destinationIndexPath: IndexPath, collectionView: UICollectionView)

could be removed

---

The final simplified version of @Vasily Bodnarchuk's in Swift 5:

Controller Part:

import UIKit

enum CellModel {
    case simple(text: String)
    case availableToDropAtEnd
}

class SecondController: UIViewController {

    private lazy var cellIdentifier = "cellIdentifier"
    private lazy var supplementaryViewIdentifier = "supplementaryViewIdentifier"
    private lazy var sections = 10
    private lazy var itemsInSection = 2
    private lazy var numberOfElementsInRow = 3

    private lazy var data: [[CellModel]] = {
        var count = 0
        return (0 ..< sections).map { _ in
            return (0 ..< itemsInSection).map { _ -> CellModel in
                count += 1
                return .simple(text: "cell \(count)")
            }
        }
    }()

    override func viewDidLoad() {
        super.viewDidLoad()

        let collectionViewFlowLayout = UICollectionViewFlowLayout()
        collectionViewFlowLayout.minimumLineSpacing = 5
        collectionViewFlowLayout.minimumInteritemSpacing = 5
        let _numberOfElementsInRow = CGFloat(numberOfElementsInRow)
        let allWidthBetwenCells = _numberOfElementsInRow == 0 ? 0 : collectionViewFlowLayout.minimumInteritemSpacing*(_numberOfElementsInRow-1)
        let width = (view.frame.width - allWidthBetwenCells)/_numberOfElementsInRow
        collectionViewFlowLayout.itemSize = CGSize(width: width, height: width)
        collectionViewFlowLayout.headerReferenceSize = CGSize(width: 0, height: 40)

        let collectionView = UICollectionView(frame: .zero, collectionViewLayout: collectionViewFlowLayout)
        collectionView.backgroundColor = .white
        view.addSubview(collectionView)
        collectionView.translatesAutoresizingMaskIntoConstraints = false
        collectionView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor).isActive = true
        collectionView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor).isActive = true
        collectionView.leftAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leftAnchor).isActive = true
        collectionView.rightAnchor.constraint(equalTo: view.safeAreaLayoutGuide.rightAnchor).isActive = true

        collectionView.register(CollectionViewCell.self, forCellWithReuseIdentifier: cellIdentifier)
        collectionView.register(SupplementaryView.self,
                                forSupplementaryViewOfKind: UICollectionView.elementKindSectionHeader,
                                withReuseIdentifier: supplementaryViewIdentifier)

        collectionView.dragInteractionEnabled = true
        collectionView.reorderingCadence = .fast
        collectionView.dropDelegate = self
        collectionView.dragDelegate = self

        collectionView.delegate = self
        collectionView.dataSource = self
    }
}



extension SecondController: UICollectionViewDelegate { }


extension SecondController: UICollectionViewDataSource {

    func numberOfSections(in collectionView: UICollectionView) -> Int {
        return data.count
    }
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return data[section].count
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellIdentifier, for: indexPath) as! CollectionViewCell
        switch data[indexPath.section][indexPath.item] {
            case .simple(let text):
                cell.label?.text = text
                cell.backgroundColor = .gray
            case .availableToDropAtEnd:
                cell.backgroundColor = UIColor.green.withAlphaComponent(0.3)
        }
        return cell
    }

    func collectionView(_ collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, at indexPath: IndexPath) -> UICollectionReusableView {
        return collectionView.dequeueReusableSupplementaryView(ofKind: kind, withReuseIdentifier: supplementaryViewIdentifier, for: indexPath)
    }
}




extension SecondController: UICollectionViewDragDelegate {

    func collectionView(_ collectionView: UICollectionView, itemsForBeginning session: UIDragSession, at indexPath: IndexPath) -> [UIDragItem] {
        let itemProvider = NSItemProvider(object: "\(indexPath)" as NSString)
        let dragItem = UIDragItem(itemProvider: itemProvider)
        dragItem.localObject = data[indexPath.section][indexPath.row]
        return [dragItem]
    }

    func collectionView(_ collectionView: UICollectionView, itemsForAddingTo session: UIDragSession, at indexPath: IndexPath, point: CGPoint) -> [UIDragItem] {
        let itemProvider = NSItemProvider(object: "\(indexPath)" as NSString)
        let dragItem = UIDragItem(itemProvider: itemProvider)
        dragItem.localObject = data[indexPath.section][indexPath.row]
        return [dragItem]
    }


    func collectionView(_ collectionView: UICollectionView, dragSessionWillBegin session: UIDragSession) {
        var itemsToInsert = [IndexPath]()
        (0 ..< data.count).forEach {
            itemsToInsert.append(IndexPath(item: data[$0].count, section: $0))
            data[$0].append(.availableToDropAtEnd)
        }
        collectionView.insertItems(at: itemsToInsert)
    }

    func collectionView(_ collectionView: UICollectionView, dragSessionDidEnd session: UIDragSession) {
        var removeItems = [IndexPath]()
        for section in 0..<data.count {
            for item in  0..<data[section].count {
                switch data[section][item] {
                    case .availableToDropAtEnd:
                        removeItems.append(IndexPath(item: item, section: section))
                    case .simple:
                        break
                }
            }
        }
        removeItems.forEach { data[$0.section].remove(at: $0.item) }
        collectionView.deleteItems(at: removeItems)
    }
    
    
}




extension SecondController: UICollectionViewDropDelegate {
    func collectionView(_ collectionView: UICollectionView, performDropWith coordinator: UICollectionViewDropCoordinator) {
        if let destinationIndexPath = coordinator.destinationIndexPath, case UIDropOperation.move = coordinator.proposal.operation{
            reorderItems(coordinator: coordinator, destinationIndexPath:destinationIndexPath, collectionView: collectionView)
        }
    }

    func collectionView(_ collectionView: UICollectionView, canHandle session: UIDropSession) -> Bool {
        return true
    }
    
    
    
    
    func collectionView(_ collectionView: UICollectionView, dropSessionDidUpdate session: UIDropSession, withDestinationIndexPath destinationIndexPath: IndexPath?) -> UICollectionViewDropProposal {
        if collectionView.hasActiveDrag, let destinationIndexPath = destinationIndexPath {
           switch data[destinationIndexPath.section][destinationIndexPath.row] {
               case .simple:
                  return UICollectionViewDropProposal(operation: .move, intent: .insertAtDestinationIndexPath)
               case .availableToDropAtEnd:
                  return UICollectionViewDropProposal(operation: .move, intent: .insertIntoDestinationIndexPath)
           }
         } 
         else { return UICollectionViewDropProposal(operation: .forbidden) }
     }

    
    
    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,
            let localObject = item.dragItem.localObject as? CellModel {

            collectionView.performBatchUpdates ({
                data[sourceIndexPath.section].remove(at: sourceIndexPath.item)
                data[destinationIndexPath.section].insert(localObject, at: destinationIndexPath.item)
                collectionView.deleteItems(at: [sourceIndexPath])
                collectionView.insertItems(at: [destinationIndexPath])
            })
        }
    }

   
}

Cell Part:

import UIKit

class CollectionViewCell: UICollectionViewCell {
    weak var label: UILabel?

    override init(frame: CGRect) {
        super.init(frame: frame)
        clipsToBounds = true
        let label = UILabel(frame: .zero)
        label.contentMode = .scaleAspectFill
        addSubview(label)
        label.translatesAutoresizingMaskIntoConstraints = false
        label.topAnchor.constraint(equalTo: topAnchor).isActive = true
        label.bottomAnchor.constraint(equalTo: bottomAnchor).isActive = true
        label.leftAnchor.constraint(equalTo: leftAnchor).isActive = true
        label.rightAnchor.constraint(equalTo: rightAnchor).isActive = true
        label.textAlignment = .center
        label.textColor = .white
        self.label = label
        layer.borderWidth = 1
        layer.borderColor = UIColor.white.cgColor
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }

    override func prepareForReuse() {
        super.prepareForReuse()
        label?.text = nil
    }
}



class SupplementaryView: UICollectionReusableView {
    
      override init(frame: CGRect) {
          super.init(frame: frame)
          backgroundColor = UIColor.blue.withAlphaComponent(0.7)
      }

      required init?(coder aDecoder: NSCoder) {
          super.init(coder: aDecoder)
      }
}