Generic types collection view with default selection [ Copy and paste it into your playground ]

CCCollectionView.swift

//: A UIKit based Playground for presenting user interface
  
import UIKit
import PlaygroundSupport

// ******************************************
//
// MARK: - Config injection
//
// ******************************************
struct CCCollectionViewConfig {
    var itemSize: CGSize?
    var minimumInteritemSpacing: CGFloat?
    var minimumLineSpacing: CGFloat?
    var allowsDefaultSelection: Bool = true
}

// ******************************************
//
// MARK: - Generic CCCollectionView
//
// ******************************************
final class CCCollectionView<T, Cell: UICollectionViewCell>: UICollectionView, UICollectionViewDataSource, UICollectionViewDelegate {

    typealias SelectHandler = (T, IndexPath?) -> Void
    
    typealias CellConfigure = (Cell, T) -> Void
    
    var contents: [T] = [] {
        didSet {
            DispatchQueue.main.async {
                self.reloadData()
                self.selectedIndexPath = IndexPath(item: (self.config.allowsDefaultSelection) ? 0 : -1, section: 0)
            }
        }
    }
    
    var configure: CellConfigure
    
    var selectHandler: SelectHandler
    
    var selectedIndexPath: IndexPath
    
    private var config: CCCollectionViewConfig
            
    private let identifier = "identifier"
        
    init(contents: [T], config: CCCollectionViewConfig, configure: @escaping CellConfigure, selectHandler: @escaping SelectHandler) {
        
        self.config = config
        self.contents = contents
        self.configure = configure
        self.selectHandler = selectHandler
        self.selectedIndexPath = IndexPath(item: (config.allowsDefaultSelection) ? 0 : -1, section: 0)
                
        let layout = UICollectionViewFlowLayout()
        
        if let size = config.itemSize {
            layout.itemSize = size
        }
        
        layout.minimumInteritemSpacing = config.minimumInteritemSpacing ?? 0
        layout.minimumLineSpacing = config.minimumLineSpacing ?? 0
        layout.scrollDirection = .vertical
        layout.sectionInset = UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 0)
        
        super.init(frame: .zero, collectionViewLayout: layout)
        
        setup()
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    private func setup() {
        register(Cell.self, forCellWithReuseIdentifier: identifier)
    
        super.delegate = self
        super.dataSource = self
                
        allowsMultipleSelection = false
        isScrollEnabled = false
        backgroundColor = .clear
    }
    
    // ******************************************
    //
    // MARK: - UICollectionViewDataSource, UICollectionViewDelegate
    //
    // ******************************************
    
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return contents.count
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: identifier, for: indexPath) as! Cell
        cell.isSelected = (selectedIndexPath == indexPath)
        let content = contents[indexPath.row]
        configure(cell, content)
        return cell
    }

    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
                
        let content = contents[indexPath.row]
        selectHandler(content, indexPath)
        
        /// If selected item is equal to current selected item, ignore it
        if selectedIndexPath == indexPath {
            return
        }
        
        /// Handle selected cell
        let selectedCell = collectionView.cellForItem(at: indexPath)
        selectedCell?.isSelected = true
        
        /// Handle deselected cell
        let deselectItem = collectionView.cellForItem(at: selectedIndexPath)
        deselectItem?.isSelected = false
    
        selectedIndexPath = indexPath
    }
}

// ******************************************
//
// MARK: - CollectionViewCell
//
// ******************************************
final class CCCollectionViewCell: UICollectionViewCell {
    
    var title: String = "" {
        didSet {
            titleLabel.text = title
        }
    }
    
    private let titleLabel: UILabel = {
        let label = UILabel()
        return label
    }()
    
    
    var _isSelected: Bool = false
    override var isSelected: Bool {
        get {
            return _isSelected
        }
        set(newValue) {
            _isSelected = newValue
            updateSelection()
        }
    }
    
    private func updateSelection() -> Void {
        contentView.layer.borderColor = isSelected ? UIColor.red.cgColor : UIColor.green.cgColor
    }
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        contentView.addSubview(titleLabel)
        contentView.layer.cornerRadius = 2.0
        contentView.layer.borderWidth = 2.0
    }
    
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}


// ******************************************
//
// MARK: - MyViewController
//
// ******************************************
class MyViewController : UIViewController {
    
    private let fakeContents = Array(repeating: "123123", count: 40)
    
    /// Collection View Config
    private lazy var config: CCCollectionViewConfig = {
        return CCCollectionViewConfig(itemSize: CGSize(width: 100, height: 30),
                                      minimumInteritemSpacing: 4.0,
                                      minimumLineSpacing: 4.0)
    }()
    
    /// Collection View
    private lazy var collectionView: CCCollectionView<String, CCCollectionViewCell> = {
        let cv = CCCollectionView<String, CCCollectionViewCell>(contents: fakeContents, config: config, configure: { (cell: CCCollectionViewCell, content) in
            cell.title = content
        }) { [weak self] (content, indexPath) in
            guard let self = self else { return }
            guard let row = indexPath?.row else { return }
        }
        return cv
    }()
    
    override func loadView() {
        let view = UIView()
        view.backgroundColor = .white
        self.view = view
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        collectionView.frame = UIScreen.main.bounds
        view.addSubview(collectionView)
        
    }
}
// Present the view controller in the Live View window
PlaygroundPage.current.liveView = MyViewController()