即使在提供布局之后,UICollectionViewDelegateFlowLayout也出现错误

'UICollectionView must be initialized with a non-nil layout parameter'

使用此ViewController

import UIKit

class SelectDesignController: UICollectionViewController, UICollectionViewDelegateFlowLayout {
    private let designCellId = "designCellId"

    override func viewDidLoad() {
        super.viewDidLoad()
        configureNavBar()
        configureUI()
        collectionView.backgroundColor = #colorLiteral(red: 0.8515156507, green: 0.9521961808, blue: 0.9503603578, alpha: 1)
        collectionView.register(DesignCategoryCell.self, forCellWithReuseIdentifier: designCellId)
    }
    @objc func handleDismiss() {
        dismiss(animated: true, completion: nil)
    }

    func configureNavBar() {
        navigationItem.leftBarButtonItem = UIBarButtonItem(image: UIImage.fontAwesomeIcon(name: .chevronLeft, style: .solid, textColor: .white, size: CGSize(width: 40, height: 40)).withRenderingMode(.alwaysOriginal), style: .plain, target: self, action: #selector(handleDismiss))
    }
    func configureUI (){
        view.backgroundColor = #colorLiteral(red: 0.8515156507, green: 0.9521961808, blue: 0.9503603578, alpha: 1)
    }
    override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: designCellId, for: indexPath) as! DesignCategoryCell
        return cell
    }
    override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 1
    }
    /** PROVIDING a LAYOUT HERE **/
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        return CGSize(width: view.frame.width, height: view.frame.height)
    }

}

我包括 SelectDesignController

let controller = SelectDesignController()
let nav = UINavigationController(rootViewController: controller)
configureNav(nav: nav, title: "Designs")
present(nav, animated: true, completion: nil)

知道吗,我错过了什么?