scrollToItem horizontal scrolling collectionView crash - swift

Question

I am having an issue with implementing a horizontal scrollToItem collectionView. I have a collectionView (menuBar) that on tap of a cell the page collectionView will horizontally scroll to the appropriate cell. On tap of the menuBar collectionViewCell the app crashes. Not sure where the error is. Thanks in advance!
// controller class
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)
}
}
// menu bar class
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

In your comment you said:
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.
That happens, because you inside your View Controller your collectionView declared as lazy, that means it will be calculated on-demand.
The problem is in initializing your collectionView (reason: 'UICollectionView must be initialized with a non-nil layout parameter')
In your view controller replace UICollectionView initialization with this code:
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
}()
P.S. As I wrote in my comment to your question, you have reference cycle. class MenuBar should hold weak reference to your view controller to prevent this.