问我在UICollectionViewController的细胞消失了

EN

import UIKit
class HeaderController {

override init(frame: CGRect) {
super.init(frame: frame)

let categoryCollectionController = CategoryCollectionController(collectionViewLayout: UICollectionViewFlowLayout())
let categoryView = categoryCollectionController.view!
categoryView.translatesAutoresizingMaskIntoConstraints = false
addSubview(categoryView)

NSLayoutConstraint.activate([
categoryView.leftAnchor.constraint(equalTo: leftAnchor),
categoryView.rightAnchor.constraint(equalTo: rightAnchor),
categoryView.topAnchor.constraint(equalTo: topAnchor),
categoryView.bottomAnchor.constraint(equalTo: bottomAnchor)
        ])
}
}



class CategoryCollectionController: UICollectionViewController, UICollectionViewDelegateFlowLayout {

    let cellID = "UID"

    override func viewDidLoad() {
        super.viewDidLoad()
        collectionView.backgroundColor = .red
        collectionView.register(CellCategory.self, forCellWithReuseIdentifier: cellID)
        if let layout = collectionViewLayout as? UICollectionViewFlowLayout {
            layout.scrollDirection = .horizontal
        }
    }

    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: cellID, for: indexPath) as! CellCategory
        return cell
    }
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        return CGSize(width: 100, height: 100)
    }
}