UICollectionView displays empty and doesn't show any cells - swift

Question

I am just testing the code to see if it can load the collection view. But id doesn't show anything. Please look at the code below and let me know where I am wrong.
import UIKit
private let reuseIdentifier = "Cell"
class FeedController: UICollectionViewController {
//MARK: - Lifecycle
override func viewDidLoad() {
super.viewDidLoad()
configureUI()
collectionView.dataSource = self
collectionView.delegate = self
self.collectionView.reloadData()
}
//MARK: - Helpers
func configureUI() {
collectionView.backgroundColor = .white
collectionView.register(UICollectionViewCell.self, forCellWithReuseIdentifier: reuseIdentifier)
}
}
//MARK:- UICollectionViewDataSource
extension FeedController {
override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return 5
}
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: reuseIdentifier, for: indexPath)
cell.backgroundColor = .systemRed
return cell
}
}
extension FeedController: UICollectionViewDelegateFlowLayout {
func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
return CGSize(width: view.frame.width, height: 200)
}
}

Answer 1

Set a breakpoint somewhere in viewDidLoad to test if it even calls any code of this class when running the app.
Normally you get an error when you set the dataSource and delegate in a UICollectionViewController, because these are already set by the controller. Because of this, move the extension lines to the main class and remove the extension.

Answer 2

You need to initialize FeedController using public init(collectionViewLayout layout: UICollectionViewLayout) UICollectionViewController initializer, else you have no layout assigned to the UICollectionView.
Wherever you are doing FeedController() you should do FeedController(collectionViewLayout: UICollectionViewFlowLayout()) or some custom UICollectionViewLayout.