无法在UIViewController中向UIImageView添加渐变

Question

在UICollectionViewCell中，我向UIImageView添加了这样的渐变：

    override func layoutSubviews() {
        super.layoutSubviews()

        if thumbnailImageView.layer.sublayers?.first == nil {
            thumbnailImageView.addGradient(firstColor: .clear, secondColor: .black)
        }
    }

我想做同样的事，但在UIViewController中，到目前为止，我只能使它在viewDidAppear上工作

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)

    if thumbnailImageView.layer.sublayers?.first == nil {
        thumbnailImageView.addGradient(firstColor: .clear, secondColor: .black)
    }
}

我希望UIImageView像我在UICollectionView中所做的那样尽快具有渐变。你知道我该怎么做吗？

extension UIView{

    func addGradient(firstColor: UIColor, secondColor: UIColor){
        clipsToBounds = true
        let gradientLayer = CAGradientLayer()
        gradientLayer.colors = [firstColor.cgColor, secondColor.cgColor]
        gradientLayer.frame = self.bounds
        gradientLayer.startPoint = CGPoint(x: 0, y: 0)
        gradientLayer.endPoint = CGPoint(x: 0, y: 1)
        self.layer.insertSublayer(gradientLayer, at: 0)
    }
}

Answer 1

您可以在viewDidLayoutSubviews中调用它>