ios - subview 未添加某些 UICollectionViewCells 和闪烁(以编程方式)

Question

我正在尝试使用 Collection View 制作自定义图像 slider 。我希望它可以重复使用。所以我制作了单独的自定义类，其中所有 collectionView 的东西。然后从 UIViewController 调用该类，如下面的代码所示。而我的 UIColletonViewCell 只包含 imageView。
问题是在第二个单元格中。 imageView 没有被添加，在第三个单元格上，它也会闪烁。我试图调试这些问题，但不能。
ImageSlider 类和 UICollectionViewCell 类在末端，带有 Collection View 的东西:

class ImageSlider: UIView {
    var imgArr = [UIImage(named: "one.jpg"), UIImage(named: "3.jpg"), UIImage(named: "two.jpg"), UIImage(named: "4.jpg")]
    var sliderCollection : UICollectionView = {
        let widthRatio : Float = 16.0
        let heightRatio : Float = 9.0
        let collecionWidth = UIScreen.main.bounds.width - 30
        let layout = UICollectionViewFlowLayout()
        let collectionView = UICollectionView(frame: CGRect(x: 15, y: 100, width: collecionWidth, height: CGFloat((Float(collecionWidth)*heightRatio)/widthRatio)), collectionViewLayout: layout)
        layout.scrollDirection = .horizontal
        layout.minimumLineSpacing = 0
        layout.minimumInteritemSpacing = 0
        collectionView.backgroundColor = .systemOrange
        collectionView.isPagingEnabled = true
//        collectionView.isScrollEnabled = true
        collectionView.register(ImageSliderCell.self, forCellWithReuseIdentifier: "ImageSliderCell")
        return collectionView
    }()
    
    
}

extension ImageSlider: UICollectionViewDelegate, UICollectionViewDataSource, UICollectionViewDelegateFlowLayout {
    func collectionView(_ collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        return imgArr.count
    }
    
    func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "ImageSliderCell", for: indexPath) as! ImageSliderCell
        
        cell.imgView.image = imgArr[indexPath.item]
//        cell.imgView.contentMode = .scaleAspectFit
        print("cell frame : ", "(\(cell.frame.width), \(cell.frame.height)")
        print("imgView frame : ", "(\(cell.imgView.frame.width), \(cell.imgView.frame.height)")
        return cell
    }
    
    func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
        return CGSize(width: collectionView.frame.width, height: collectionView.frame.height)
    }
    
}

class ImageSliderCell: UICollectionViewCell {
    var imgView = UIImageView()
    
//    override func awakeFromNib() {
//        self.addSubview(imgView)
//    }
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        imgView.frame = frame
        self.addSubview(imgView)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

这是 ViewController，我在其中调用 ImageSlider() 类。

class ImageSliderVC: UIViewController, UICollectionViewDelegate {
    
    let imageSlider = ImageSlider()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        self.view.addSubview(imageSlider.sliderCollection)
        imageSlider.sliderCollection.delegate = imageSlider
        imageSlider.sliderCollection.dataSource = imageSlider
        imageSlider.sliderCollection.reloadData()
    }
}

Answer 1

看起来它在没有约束的情况下无法工作，因为 UICollectionViewCell 可以用零帧创建，并将其转换为单元格内的 imageView。您需要向 imageView 添加约束以使其可见。

extension UIView {
    
    func centerX(inView view: UIView, constant: CGFloat = 0) {
        translatesAutoresizingMaskIntoConstraints = false
        centerXAnchor.constraint(equalTo: view.centerXAnchor, constant: constant).isActive = true
    }
    
    func centerY(inView view: UIView, constant: CGFloat = 0) {
        translatesAutoresizingMaskIntoConstraints = false
        centerYAnchor.constraint(equalTo: view.centerYAnchor, constant: constant).isActive = true
    }
    
    func setDimensions(height: CGFloat, width: CGFloat) {
        translatesAutoresizingMaskIntoConstraints = false
        heightAnchor.constraint(equalToConstant: height).isActive = true
        widthAnchor.constraint(equalToConstant: width).isActive = true
    }
    
    func setHeight(_ height: CGFloat) {
        translatesAutoresizingMaskIntoConstraints = false
        heightAnchor.constraint(equalToConstant: height).isActive = true
    }
}

class ImageSliderCell: UICollectionViewCell {
    var imgView = UIImageView()
    
    
    override init(frame: CGRect) {
        super.init(frame: frame)
  
        self.addSubview(imgView)
        // not sure about the right size of image ...
        imgView.setDimensions(height: 100.0, width: 100.0)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}