ios - 无法将渐变添加到 UIViewController 中的 UIImageView

Question

在 UICollectionViewCell 中，我向 UIImageView 添加渐变，如下所示:

    override func layoutSubviews() {
        super.layoutSubviews()

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

我想做同样的事情，但是在 UIViewController 中，到目前为止我只能让它在 viewDidAppear 上工作

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

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

我想让 UIImageView 像我在 UICollectionView 中那样显示渐变。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

可以在viewDidLayoutSubviews中调用