Scrolling to a collectionView to a specie Index - ios

Question

I have a collectionView with a number of cells and when I load it I want to select a specific cell, show it as selected and scroll the collection view to the that selected cell's location without having to do the scrolling myself.
I can show the cell as selected but the scrolling doesn't seem to work from the provided function.
This is my attempt to doing it.
class RepsCellView: UICollectionViewCell, UICollectionViewDataSource, UICollectionViewDelegate, UICollectionViewDelegateFlowLayout {
lazy var repsValuesCollectionView: UICollectionView = {
let layout = UICollectionViewFlowLayout()
layout.scrollDirection = .horizontal
let collectionView = UICollectionView(frame: .zero, collectionViewLayout: layout)
collectionView.backgroundColor = UIColor.black
collectionView.showsHorizontalScrollIndicator = false
collectionView.translatesAutoresizingMaskIntoConstraints = false
return collectionView
}()
override init(frame: CGRect) {
super.init(frame: frame)
setupViews()
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
func setupViews() {
addSubview(repsValuesCollectionView)
//...
// Cell
let selectedIndex = IndexPath(item: 19, section: 0)
repsValuesCollectionView.selectItem(at: selectedIndex, animated: true, scrollPosition: [.centeredHorizontally, .centeredVertically])
}
// CollectionView DataSource Functions
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return 100
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath)
return cell
}
}
Thanks in advance.

Answer 1

what ViewController event method are you using to run your code?
Anyway I could scroll it placing your code in the ViewController event method viewDidAppear method.
class CollectionViewController: UICollectionViewController {
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
let cellToSelect = IndexPath(item: 99, section: 0)
self.collectionView?.scrollToItem(at: cellToSelect, at: [.centeredHorizontally, .centeredVertically], animated: true)
}
override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return 1
}
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath) as! RepsCellView
cell.setupViews() // added this line
return cell
}
}