Align the collectionviewcells center - ios

Question

I current have a collectionview attached to a array of strings. I want to align these cells center regardless of the number of things in the array. I am not sure how to do it, and where to do it.
import UIKit
class MyButtonCell: UICollectionViewCell{
#IBOutlet weak var buttonOne: UIButton!
#IBOutlet weak var targetButton: UIButton!
var callback: (() -> ())?
override init(frame: CGRect) {
super.init(frame: frame)
commonInit()
}
required init?(coder: NSCoder) {
super.init(coder: coder)
commonInit()
}
func commonInit() -> Void {
contentView.layer.borderWidth = 1
contentView.layer.borderColor = UIColor.black.cgColor
}
#IBAction func buttonTapped(_ sender: UIButton) {
callback?()
}
}
class StevenViewController: UIViewController, UICollectionViewDelegate, UICollectionViewDataSource {
let buttonTitles: [String] = [
"4", "6", "7", "8"
]
var targetButtonTitles: [String] = [
"", "", "", ""
]
var current:String = ""
#IBOutlet var collectionView: UICollectionView!
#IBOutlet var targetCollection: UICollectionView!
override func viewDidLoad() {
super.viewDidLoad()
targetCollection.delegate = self
targetCollection.dataSource = self
collectionView.delegate = self
collectionView.dataSource = self
collectionView.tag = 1
targetCollection.tag = 2
}
func centerItemsInCollectionView(cellWidth: Double, numberOfItems: Double, spaceBetweenCell: Double, collectionView: UICollectionView) -> UIEdgeInsets {
let totalWidth = cellWidth * numberOfItems
let totalSpacingWidth = spaceBetweenCell * (numberOfItems - 1)
let leftInset = (collectionView.frame.width - CGFloat(totalWidth + totalSpacingWidth)) / 2
let rightInset = leftInset
return UIEdgeInsets(top: 0, left: leftInset, bottom: 0, right: rightInset)
}
func numberOfSections(in collectionView: UICollectionView) -> Int {
return 1
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
if collectionView.tag == 1 {
return buttonTitles.count
} else {
return targetButtonTitles.count
}
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
// set the button title (and any other properties)
if collectionView.tag == 1 {
// Setup here your cell
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "myCellID", for: indexPath) as! MyButtonCell
cell.callback = {
print("Button was tapped at \(indexPath)")
self.targetButtonTitles[indexPath.item] = self.buttonTitles[indexPath.item]
//print(self.targetButtonTitles)
self.current = self.buttonTitles[indexPath.item]
print(self.current)
//collectionView.reloadData()
// do what you want when the button is tapped
}
cell.buttonOne.setTitle(buttonTitles[indexPath.item], for: [])
return cell
} else {
// Setup here your targetCell
let targetCell = targetCollection.dequeueReusableCell(withReuseIdentifier: "myCellID", for: indexPath) as! MyButtonCell
targetCell.callback = {
if self.current != ""{
self.targetButtonTitles[indexPath.item] = self.current
print(self.targetButtonTitles)
targetCell.targetButton.setTitle(self.targetButtonTitles[indexPath.item], for: [])
self.current = ""
}else{
self.targetButtonTitles[indexPath.item] = ""
targetCell.targetButton.setTitle(self.targetButtonTitles[indexPath.item], for: [])
}
}
return targetCell
}
}
}
As you can see, right now they are just starting from the left. So, How should I align them in the middle.