晚上好，
我一直试图弄清楚当我按下按钮时如何淡化屏幕，以便为子视图提供更清晰的外观。我研究了 zPositions，我认为在我的代码中实现这个功能会有所帮助。当我运行我的代码时，整个屏幕都会消失。我希望在背景褪色时出现一个圆形进度环。我将展示一张图片和我的代码。先感谢您。
@objc func handlePost() {
let center = view.center
let trackLayer = CAShapeLayer()
let circularPath = UIBezierPath(arcCenter: center, radius: 100, startAngle: -CGFloat.pi / 2, endAngle: 2 * CGFloat.pi, clockwise: true)
blackScreen=UIView(frame: self.view.bounds)
blackScreen.backgroundColor=UIColor(white: 0, alpha: 0.8)
blackScreen.isHidden=true
self.navigationController?.view.addSubview(blackScreen)
blackScreen.layer.zPosition=50
blackScreen.isHidden=false
self.view.backgroundColor = UIColor.white
trackLayer.path = circularPath.cgPath
trackLayer.strokeColor = UIColor.lightGray.cgColor
trackLayer.lineWidth = 10
trackLayer.fillColor = UIColor.clear.cgColor
trackLayer.lineCap = kCALineCapRound
// The zPosition is supposed to bring this layer to the front.
trackLayer.zPosition = 100
shapeLayer.path = circularPath.cgPath
shapeLayer.strokeColor = GREEN_Theme.cgColor
shapeLayer.lineWidth = 10
shapeLayer.fillColor = UIColor.clear.cgColor
shapeLayer.lineCap = kCALineCapRound
shapeLayer.strokeEnd = 0
// The zPosition is supposed to bring this layer to the front.
shapeLayer.zPosition = 100
let basicAnimation = CABasicAnimation(keyPath: "strokeEnd")
basicAnimation.toValue = 1
basicAnimation.duration = 2
basicAnimation.fillMode = kCAFillModeForwards
basicAnimation.isRemovedOnCompletion = false
shapeLayer.add(basicAnimation, forKey: "dataSearch")
shapeLayer.removeAnimation(forKey: "finished")
view.layer.addSublayer(trackLayer)
view.layer.addSublayer(shapeLayer)
}