Why won't my swift collection view show anything - swift

Question

I want to make a simple collection view just showing some pictures but the cells wont show
import UIKit
final class HomePageViewController: UICollectionViewController {
// MARK: - Properties
override func loadView() {
super.loadView()
let collectionView = UICollectionView(frame: .zero, collectionViewLayout: UICollectionViewFlowLayout())
collectionView.translatesAutoresizingMaskIntoConstraints = false
self.view.addSubview(collectionView)
NSLayoutConstraint.activate([
collectionView.topAnchor.constraint(equalTo: self.view.topAnchor),
collectionView.bottomAnchor.constraint(equalTo: self.view.bottomAnchor),
collectionView.leadingAnchor.constraint(equalTo: self.view.leadingAnchor),
collectionView.trailingAnchor.constraint(equalTo: self.view.trailingAnchor),
])
self.collectionView = collectionView
}
override func viewDidLoad() {
super.viewDidLoad()
self.collectionView.backgroundColor = .white
self.collectionView.dataSource = self
self.collectionView.delegate = self
self.collectionView.register(HomePageCell.self, forCellWithReuseIdentifier: "HomePageCell")
}
// MARK: - Private
override func numberOfSections(in collectionView: UICollectionView) -> Int {
return 1
}
override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
return 10
}
override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "HomePageCell", for: indexPath) as! HomePageCell
cell.Picture.image = UIImage(named: "songpic-1")
return cell
}
}
extension HomePageViewController: UICollectionViewDelegateFlowLayout {
func collectionView(_ collectionView: UICollectionView,
layout collectionViewLayout: UICollectionViewLayout,
sizeForItemAt indexPath: IndexPath) -> CGSize {
return CGSize(width: collectionView.bounds.size.width - 16, height: 200)
}
func collectionView(_ collectionView: UICollectionView,
layout collectionViewLayout: UICollectionViewLayout,
minimumLineSpacingForSectionAt section: Int) -> CGFloat {
return 8
}
func collectionView(_ collectionView: UICollectionView,
layout collectionViewLayout: UICollectionViewLayout,
minimumInteritemSpacingForSectionAt section: Int) -> CGFloat {
return 0
}
func collectionView(_ collectionView: UICollectionView,
layout collectionViewLayout: UICollectionViewLayout,
insetForSectionAt section: Int) -> UIEdgeInsets {
return UIEdgeInsets.init(top: 8, left: 8, bottom: 8, right: 8)
}
}
import UIKit
class HomePageCell: UICollectionViewCell {
#IBOutlet weak var Picture: UIImageView!
override init(frame: CGRect) {
super.init(frame: frame)
let Picture = UIImageView(frame: .zero)
Picture.translatesAutoresizingMaskIntoConstraints = false
self.contentView.addSubview(Picture)
NSLayoutConstraint.activate([
Picture.topAnchor.constraint(equalTo: self.contentView.topAnchor),
Picture.bottomAnchor.constraint(equalTo: self.contentView.bottomAnchor),
Picture.leadingAnchor.constraint(equalTo: self.contentView.leadingAnchor),
Picture.trailingAnchor.constraint(equalTo: self.contentView.trailingAnchor),
])
self.contentView.backgroundColor = .lightGray
}
required init?(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
fatalError("Interface Builder is not supported!")
}
override func awakeFromNib() {
super.awakeFromNib()
// Initialization code
}
override func prepareForReuse() {
super.prepareForReuse()
}
}

Answer 1

You can delete/comment your loadView() implementation and things should work just fine. You will still get a UICollectionView to work with.
The loadView() implementation is supposed to provide a UIView instance that's to be assigned to UIViewController.view property. In your implementation however, we are using it via self.view directly without assigning it first.
From UIViewController.loadView() docs -
You can override this method in order to create your views manually. If you choose to do so, assign the root view of your view hierarchy to the view property. The views you create should be unique instances and should not be shared with any other view controller object. Your custom implementation of this method should not call super.
What to do if this still doesn't show up?
Check using View Hierarchy Debugger that at run time your collectionView has non-zero width & height values. If any of the width OR height is zero, you will run into this issue.