无法向 UIViewController 中的 UIImageView 添加渐变

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UIViewController，到目前为止，我只能让它在viewDidAppear

override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
if thumbnailImageView.layer.sublayers?.first == nil {
thumbnailImageView.addGradient(firstColor: .clear, secondColor: .black)
}
}

我想UIImageView尽快获得渐变，就像我在UICollectionView中所做的那样.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

你可以用viewDidLayoutSubviews来调用它