UICollectionView performs batch update with custom floating animation of the new cell

UICollectionView+animationOnCellInsertion

import UIKit

private func makeRandomData() -> [MyModel] { [ MyModel(color: .random) ] }

private final class MyUICollectionViewFlowLayout: UICollectionViewFlowLayout {
    var insertingIndexPaths = [IndexPath]()
    
    override func prepare(
        forCollectionViewUpdates updateItems: [UICollectionViewUpdateItem]
    ) {
        super.prepare(forCollectionViewUpdates: updateItems)
        
        insertingIndexPaths.removeAll()
        
        updateItems.forEach { update in
            guard let indexPath = update.indexPathAfterUpdate,
                  update.updateAction == .insert else {
                return
            }
            insertingIndexPaths.append(indexPath)
        }
    }
    
    override func finalizeCollectionViewUpdates() {
        super.finalizeCollectionViewUpdates()
        
        insertingIndexPaths.removeAll()
    }
    
    override func initialLayoutAttributesForAppearingItem(
        at itemIndexPath: IndexPath
    ) -> UICollectionViewLayoutAttributes? {
        let attributes = super.initialLayoutAttributesForAppearingItem(at: itemIndexPath)
        if insertingIndexPaths.contains(itemIndexPath) {
            attributes?.alpha = 0.0
            attributes?.transform
                = CGAffineTransform(
                    translationX: 200,
                    y: 0
                )
        }
        return attributes
    }
}

final class ViewController: UIViewController {
    private let collectionView: MyCollectionViewController = {
        let layout = MyUICollectionViewFlowLayout()
        layout.scrollDirection = .horizontal
        return MyCollectionViewController(collectionViewLayout: layout)
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        setupUI()
    }
}

private extension ViewController {
    func setupUI() {
        view.addSubview(collectionView.view)
        collectionView.view.translatesAutoresizingMaskIntoConstraints = false
        
        NSLayoutConstraint.activate([
            collectionView.view.bottomAnchor.constraint(equalTo: view.bottomAnchor),
            collectionView.view.heightAnchor.constraint(equalToConstant: 300),
            collectionView.view.leftAnchor.constraint(equalTo: view.leftAnchor),
            collectionView.view.rightAnchor.constraint(equalTo: view.rightAnchor)
        ])
        
        collectionView.data = makeRandomData()
        collectionView.collectionView.reloadData()
    }
}

private final class MyCollectionViewController: UICollectionViewController {
    var data: [MyModel] = []
    
    override init(collectionViewLayout layout: UICollectionViewLayout) {
        super.init(collectionViewLayout: layout)
        
        collectionView.contentInset = UIEdgeInsets(top: 0, left: 10, bottom: 0, right: 180)
        collectionView.register(MyCell.self, forCellWithReuseIdentifier: MyCell.identifier)
    }
    
    @available(*, unavailable)
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func collectionView(
        _ collectionView: UICollectionView,
        numberOfItemsInSection section: Int
    ) -> Int {
        data.count
    }
    
    override func collectionView(
        _ collectionView: UICollectionView,
        cellForItemAt indexPath: IndexPath
    ) -> UICollectionViewCell {
        guard let cell
                = collectionView.dequeueReusableCell(
                    withReuseIdentifier: MyCell.identifier,
                    for: indexPath
                ) as? MyCell else {
            return UICollectionViewCell()
        }
        cell.configure(with: data[indexPath.row])
        return cell
    }
    
    
    override func collectionView(
        _ collectionView: UICollectionView,
        didSelectItemAt indexPath: IndexPath
    ) {
        guard indexPath.row == data.count - 1 else {
            return
        }
        let oldData = data
        let newData = data + makeRandomData()
        data = newData
        
        UIView.animate(
            withDuration: 1.1,
            delay: 0,
            usingSpringWithDamping: 0.71,
            initialSpringVelocity: 0.3,
            options: [.allowUserInteraction, .layoutSubviews, .curveEaseInOut]
        ) {
            collectionView.performBatchUpdates { [weak self] in
                let diff = newData.difference(from: oldData)
                diff.forEach { change in
                    switch change {
                    case let .remove(offset, _, _):
                        let indexes = [IndexPath(item: offset, section: 0)]
                        self?.collectionView.deleteItems(at: indexes)
                    case let .insert(offset, _, _):
                        let indexes = [IndexPath(item: offset, section: 0)]
                        self?.collectionView.insertItems(at: indexes)
                    }
                }
            } completion: { _ in }
        } completion: { _ in }
    }
}

extension MyCollectionViewController: UICollectionViewDelegateFlowLayout {
    func collectionView(
        _ collectionView: UICollectionView,
        layout collectionViewLayout: UICollectionViewLayout,
        sizeForItemAt indexPath: IndexPath
    ) -> CGSize {
        CGSize(width: 200, height: 200)
    }
}

private struct MyModel: Hashable, Identifiable {
    let id: UUID = UUID()
    let color: UIColor
    
    func hash(into hasher: inout Hasher) {
        hasher.combine(color)
        hasher.combine(id)
    }
}

private final class MyCell: UICollectionViewCell {
    func configure(with model: MyModel) {
        contentView.backgroundColor = model.color
    }
}

private extension UICollectionViewCell {
    static var identifier: String {
        String(describing: self)
    }
}

private extension UIColor {
    static var random: UIColor {
        UIColor(red: .random(in: 0...1),
                green: .random(in: 0...1),
                blue: .random(in: 0...1),
                alpha: 1.0)
    }
}