NumbersCollectionView.swift

import SwiftUI

struct NumbersCollectionView : UIViewRepresentable {
    @Binding var numbers: [Int]
    
    func makeUIView(context: Context) -> UICollectionView {
        let layout = UICollectionViewFlowLayout()
        let collectionView = UICollectionView(frame: .zero, collectionViewLayout: layout)
        collectionView.backgroundColor = .white
        
        collectionView.register(NumberCell.self, forCellWithReuseIdentifier: "Cell")
        
        let dataSource = UICollectionViewDiffableDataSource<Int, Int>(collectionView: collectionView) { (collectionView, indexPath, id) -> UICollectionViewCell? in
            let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath) as! NumberCell
            
            cell.number = id
            
            return cell
        }
        
        context.coordinator.dataSource = dataSource
        collectionView.dataSource = dataSource
        
        return collectionView
    }
    
    func updateUIView(_ uiView: UICollectionView, context: Context) {
        let snapshot = NSDiffableDataSourceSnapshot<Int, Int>()
        snapshot.appendSections([0])
        snapshot.appendItems(numbers)
        
        context.coordinator.dataSource.apply(snapshot, animatingDifferences: true)
    }
    
    func makeCoordinator() -> Coordinator {
        return Coordinator()
    }
    
    final class Coordinator: NSObject {
        var dataSource: UICollectionViewDiffableDataSource<Int, Int>!
    }
}

private final class NumberCell: UICollectionViewCell {
    var number: Int? {
        didSet {
            numberLabel.text = number.map(String.init)
        }
    }
    
    private let numberLabel = UILabel()
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        
        contentView.addSubview(numberLabel)
        
        contentView.backgroundColor = .systemYellow
        
        numberLabel.translatesAutoresizingMaskIntoConstraints = false
        
        NSLayoutConstraint.activate([
            numberLabel.centerXAnchor.constraint(equalTo: contentView.centerXAnchor),
            numberLabel.centerYAnchor.constraint(equalTo: contentView.centerYAnchor)
        ])
    }
    
    override func layoutSubviews() {
        super.layoutSubviews()
        
        contentView.layer.cornerRadius = contentView.frame.width / 2.0
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}