我正在尝试添加一些子层到根视图层。想法是混合一个黄色和红色阴影的视图。
我试过这个：
class ViewController: UIViewController {
@IBOutlet weak var testView: UIView! {
didSet {
testView.backgroundColor = .white
testView.layer.cornerRadius = 10.0
}
}
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .black
testView.layer.shadowColor = UIColor.yellow.cgColor
testView.layer.shadowOpacity = 1.0
testView.layer.shadowRadius = 24.0
let layer1 = CALayer()
layer1.frame = testView.bounds
layer1.shadowColor = UIColor.red.cgColor
layer1.shadowOpacity = 1.0
layer1.shadowRadius = 24.0
testView.layer.addSublayer(layer1)
}
}
但只出现根层（黄色的），而不是红色的子层：
为什么会出现这种情况？谢谢你的帮助
两个问题...
TestView可能不是ViewDidLoad()中的最终大小...您应该在ViewDidLoad之后添加层，或者子类UIView并在LayoutSubViews快速尝试一下：
class SubLayerShadowViewController: UIViewController {
let testView = UIView()
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = .black
testView.translatesAutoresizingMaskIntoConstraints = false
view.addSubview(testView)
let g = view.safeAreaLayoutGuide
NSLayoutConstraint.activate([
testView.widthAnchor.constraint(equalToConstant: 240.0),
testView.heightAnchor.constraint(equalTo: testView.widthAnchor),
testView.centerXAnchor.constraint(equalTo: g.centerXAnchor),
testView.centerYAnchor.constraint(equalTo: g.centerYAnchor),
])
testView.backgroundColor = .white
testView.layer.cornerRadius = 10.0
testView.layer.shadowColor = UIColor.yellow.cgColor
testView.layer.shadowOpacity = 1.0
testView.layer.shadowRadius = 24.0
// move this out of viewDidLoad()
//let layer1 = CALayer()
//layer1.cornerRadius = 10.0
//layer1.frame = testView.bounds
//layer1.shadowColor = UIColor.red.cgColor
//layer1.shadowOpacity = 1.0
//layer1.shadowRadius = 24.0
//testView.layer.addSublayer(layer1)
}
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
let layer1 = CALayer()
layer1.cornerRadius = 10.0
layer1.frame = testView.bounds
layer1.shadowColor = UIColor.red.cgColor
layer1.shadowOpacity = 1.0
layer1.shadowRadius = 24.0
// set this layer's backgroundColor to the view's backgroundColor
layer1.backgroundColor = testView.backgroundColor?.cgColor
testView.layer.addSublayer(layer1)
}
}
