Multiple CollectionViews in one ViewController - ios

Question

I try to show multiple collection views in one ViewController, but I get crash with error:
Thread 1: Exception: "could not dequeue a view of kind: UICollectionElementKindCell with identifier MainCell - must register a nib or a class for the identifier or connect a prototype cell in a storyboard"
I registered all the cells in Storyboard and this is my code for ViewController:
class ViewController: UIViewController, UICollectionViewDataSource, UICollectionViewDelegate, UICollectionViewDelegateFlowLayout {
#IBOutlet weak var collectionView: UICollectionView!
#IBOutlet weak var horizontalNumbers: UICollectionView!
#IBOutlet weak var verticalNumbers: UICollectionView!
override func viewDidLoad() {
super.viewDidLoad()
collectionView.delegate = self
collectionView.dataSource = self
horizontalNumbers.delegate = self
horizontalNumbers.dataSource = self
verticalNumbers.delegate = self
verticalNumbers.dataSource = self
}
func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
if collectionView == collectionView {
return 81
} else {
return 9
}
}
func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
if collectionView == collectionView {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "MainCell", for: indexPath) as! CollectionViewCell
cell.backgroundColor = .systemGreen
return cell
} else if collectionView == horizontalNumbers {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Horizontal", for: indexPath) as! HorizontalNumbersCell
return cell
} else {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Vertical", for: indexPath) as! VerticalNumbersCell
return cell
}
}
}
I checked everything twice and looked for some examples of code, but don't release why I get crash.

Answer 1

You need to register cell for all three collectionView.Take the collectionView for example.
try
collectionView.register(UINib(nibName: "CollectionViewCell", bundle: nil), forCellWithReuseIdentifier: "MainCell") // if it is loaded in nib, and nib name is CollectionViewCell
or
collectionView.register(CollectionViewCell.self, forCellWithReuseIdentifier: "MainCell") // if it is written just in code
in the viewDidLoad.
Do the same thing for the horizontalNumbers, etc.
Check https://developer.apple.com/documentation/uikit/uicollectionview/1618089-register for more details.