scrollToItem коллекция с горизонтальной прокруткой

Question

У меня возникли проблемы с реализацией горизонтального scrollToItem collectionView. У меня есть collectionView (menuBar), который при нажатии на ячейку pageViewView страницы будет горизонтально прокручивать до соответствующей ячейки. При нажатии на панель меню CollectionViewCell приложение вылетает. Не уверен, где ошибка. Заранее спасибо!

// класс контроллера

class CurrentUserPlaceDetailsVC: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {

    var titleText: String?

    let cellId = "cellId"

    // UI elements
    lazy var contentCollectionView: UICollectionView = {
        let cv = UICollectionView()
        cv.backgroundColor = UIColor.red
        cv.layer.zPosition = 0
        cv.translatesAutoresizingMaskIntoConstraints = false
        cv.layer.masksToBounds = true
        return cv
    }()

    override func viewDidLoad() {
        super.viewDidLoad()

        setupMenuBar()
        setupCollectionView()

    }

    func scrollToMenuIndex(_ menuIndex: Int) {
        let indexPath = IndexPath(item: menuIndex, section: 0)
        contentCollectionView.scrollToItem(at: indexPath, at: UICollectionViewScrollPosition(), animated: true)
    }

    lazy var menuBar: MenuBar = {
        let mb = MenuBar()
        mb.currentUserPlaceDetailsVC = self
        return mb
    }()

    private func setupMenuBar() {
        view.addSubview(menuBar)
        view.addConstraintsWithFormat("H:|[v0]|", views: menuBar)
        view.addConstraintsWithFormat("V:|[v0(114)]", views: menuBar)
    }

    func setupCollectionView() {

        let layout: UICollectionViewFlowLayout = UICollectionViewFlowLayout()

        layout.scrollDirection = .horizontal
        layout.minimumLineSpacing = 0
//        layout.sectionInset = UIEdgeInsets(top: 0, left: 10, bottom: 10, right: 10)
        layout.itemSize = CGSize(width: self.view.frame.width, height: self.view.frame.height)

        let contentCollectionView:UICollectionView = UICollectionView(frame: self.view.frame, collectionViewLayout: layout)
        contentCollectionView.dataSource = self
        contentCollectionView.delegate = self

        // register cells
        contentCollectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: "cellId")
        contentCollectionView.backgroundColor = .white
//        contentCollectionView.scrollIndicatorInsets = UIEdgeInsets(top:114, left: 10, bottom: 10, right: 10)
        self.view.addSubview(contentCollectionView)

        _ = contentCollectionView.anchor(view.topAnchor, left: view.leftAnchor, bottom: view.bottomAnchor, right: view.rightAnchor, topConstant: 114, leftConstant: 0, bottomConstant: 0, rightConstant: 0, widthConstant: 0, heightConstant: 0)
        view.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
        contentCollectionView.isPagingEnabled = true
    }

    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        print(scrollView.contentOffset.x)
        menuBar.horizontalBarLeftAnchorConstraint?.constant = scrollView.contentOffset.x / 4
    }

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 4
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let myCell = collectionView.dequeueReusableCell(withReuseIdentifier: "cellId", for: indexPath)
        let colors: [UIColor] = [.blue, .red, .yellow, .green]
        myCell.backgroundColor = colors[indexPath.item]
        return myCell
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        return CGSize(width: view.frame.width, height: view.frame.height)
    }

}

// класс строки меню

class MenuBar: UIView, UICollectionViewDataSource, UICollectionViewDelegate, UICollectionViewDelegateFlowLayout {

    lazy var collectionView: UICollectionView = {
        let layout = UICollectionViewFlowLayout()
        layout.minimumLineSpacing = 0
        layout.headerReferenceSize = .zero
        layout.sectionInset = .zero
        let cv = UICollectionView(frame: .zero, collectionViewLayout: layout)
        cv.backgroundColor = .green
        cv.dataSource = self
        cv.delegate = self
        return cv
    }()

    let cellId = "cellId"

    var currentUserPlaceDetailsVC: CurrentUserPlaceDetailsVC?

    override init(frame: CGRect) {
        super.init(frame: frame)

        collectionView.register(MenuCell.self, forCellWithReuseIdentifier: cellId)

        addSubview(collectionView)
        addConstraintsWithFormat("H:|[v0]|", views: collectionView)
        addConstraintsWithFormat("V:|[v0]|", views: collectionView)

        let selectedIndexPath = IndexPath(item: 0, section: 0)
        collectionView.selectItem(at: selectedIndexPath, animated: false, scrollPosition: UICollectionViewScrollPosition())

        setupHorizontalBar()
    }

    var horizontalBarLeftAnchorConstraint: NSLayoutConstraint?

    func setupHorizontalBar() {
        let horizontalBarView = UIView()
        horizontalBarView.backgroundColor = .white
        horizontalBarView.translatesAutoresizingMaskIntoConstraints = false
        addSubview(horizontalBarView)

        horizontalBarLeftAnchorConstraint = horizontalBarView.leftAnchor.constraint(equalTo: self.leftAnchor)
        horizontalBarLeftAnchorConstraint?.isActive = true

        horizontalBarView.bottomAnchor.constraint(equalTo: self.bottomAnchor).isActive = true
        horizontalBarView.widthAnchor.constraint(equalTo: self.widthAnchor, multiplier: 1/4).isActive = true
        horizontalBarView.heightAnchor.constraint(equalToConstant: 4).isActive = true

    }

    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        print(indexPath.item)
        let x = CGFloat(indexPath.item) * frame.width / 4
        horizontalBarLeftAnchorConstraint?.constant = x

        UIView.animate(withDuration: 0.75, delay: 0, usingSpringWithDamping: 1, initialSpringVelocity: 1, options: .curveEaseOut, animations: {
            self.layoutIfNeeded()
        }, completion: nil)

        currentUserPlaceDetailsVC?.scrollToMenuIndex(indexPath.item)

    }

    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 4
    }

    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellId, for: indexPath) as! MenuCell
        cell.imageView.image = UIImage(named: imageNames[indexPath.item])?.withRenderingMode(.alwaysTemplate)
        cell.tintColor = UIColor.rgb(91, green: 14, blue: 13)

        return cell
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        return CGSize(width: frame.width / 4, height: frame.height)
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, minimumInteritemSpacingForSectionAt section: Int) -> CGFloat {
        return 0
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

}

Answer 1

В своем комментарии вы сказали:

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'UICollectionView must be initialized with a non-nil layout parameter'. I believe there is something wrong in my func scrollToMenuIndex()... when I remove that func the app does not crash.

Это происходит потому, что внутри вашего View Controller ваш collectionView объявлен как ленивый, это означает, что он будет рассчитан по требованию. Проблема в инициализации вашего collectionView (reason: 'UICollectionView must be initialized with a non-nil layout parameter')

В вашем представлении контроллера замените инициализацию UICollectionView на этот код:

lazy var contentCollectionView: UICollectionView = {
    let layout = UICollectionViewFlowLayout()
    let cv = UICollectionView(frame: .zero, collectionViewLayout: layout)
    cv.backgroundColor = UIColor.red
    cv.layer.zPosition = 0
    cv.translatesAutoresizingMaskIntoConstraints = false
    cv.layer.masksToBounds = true
    return cv
}()

PS Как я уже писал в своем комментарии к вашему вопросу, у вас есть справочный цикл. учебный класс MenuBar должен держать слабую ссылку на ваш контроллер представления, чтобы предотвратить это.