collectionView:layout:sizeForItemAt 未调用 swift 4 iOS 11

Question

class HomeController: UICollectionViewController, UICollectionViewDelegateFlowLayout {

    private let cellId = "cellId"

    override func viewDidLoad() {
        super.viewDidLoad()

        collectionView?.register(Cell.self, forCellWithReuseIdentifier: cellId)
        collectionView?.backgroundColor = UIColor.red
    }

    override func numberOfSections(in collectionView: UICollectionView) -> Int {
        return 1
    }

    override func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return 3
    }

    override func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: cellId, for: indexPath) as! Cell
        return cell
    }

    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        return CGSize(width: 150, height: 150)
    }
}

class Cell: UICollectionViewCell {
    override init(frame: CGRect) {
        super.init(frame: frame)

        setup()
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    func setup() {
        backgroundColor = UIColor.black
    }
}

numberOfSections 和 numberOfItemsInSection 被调用（根据断点），但 cellForItemAt 和 sizeForItemAt 从未被调用。

我看不出有什么不对吗？

更新：（我如何在 AppDelegate 中创建 HomeController）

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {

    window = UIWindow(frame: UIScreen.main.bounds)
    window?.makeKeyAndVisible()

    let layout = UICollectionViewLayout()
    let homeController = HomeController(collectionViewLayout: layout)
    window?.rootViewController = UINavigationController(rootViewController: homeController)

    return true
}

Answer 1

您正在使用 UICollectionViewLayout()

你应该use -

 let layout = UICollectionViewFlowLayout()

collectionView:layout:sizeForItemAt 未调用 swift 4 iOS 11

collectionView:layout:sizeForItemAt not called swift 4 iOS 11

ios

uicollectionview

swift4

ios11