对于加载视图围绕圆形视图旋转的部分，可以使用UIBezierPath，并根据其路径创建一个CAKeyframeAnimation，看看这个实现，希望能有所帮助。

class LoadingViewController: UIViewController {

    var circlePath: UIBezierPath!
    lazy var loader = makeLoader()
    lazy var centerView = makeCenterView()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        setup()
    }
    
    func makeLoader() -> UIButton {
        let padding: CGFloat = 100
        let width = self.view.frame.width - (2 * padding)
        let b = UIButton(frame: CGRect(x: padding, y: 200, width: width, height: 50))
        b.addTarget(self, action: #selector(didTap), for: .touchUpInside)
        b.backgroundColor = .blue
        return b
    }
    
    func makeCenterView() -> UIView {
        let width: CGFloat = 20
        let height: CGFloat = 20
        let x = self.view.center.x - width/2
        let y = self.view.center.y - height/2
        
        let view = UIView(frame: CGRect(x: x, y: y, width: width, height: height))
        view.backgroundColor = .green
        return view
    }

    func setup() {
        //create a UIBezierPath with a center that is at the center of the green view and a radius that has a length as the distance between the green view and the blue view.
        let arcCenterX = centerView.center.x
        let arcCenterY = centerView.center.y
        let arcCenter = CGPoint(x: arcCenterX, y: arcCenterY)
        let radius = arcCenterY - loader.center.y
        let startAngle = -CGFloat.pi/2
        let endAngle = CGFloat.pi*(1.5)
        
        let arcPath = UIBezierPath(arcCenter: arcCenter, radius:  radius, startAngle: startAngle, endAngle: endAngle, clockwise: true)
        self.circlePath = arcPath
        
        self.view.addSubview(loader)
        self.view.addSubview(centerView)
    }
    
    @objc func didTap() {
        //create a CAKeyframeAnimation with a path that matches the UIBezierPath above.
        let loadAnimation = CAKeyframeAnimation(keyPath: "position")
        loadAnimation.path = self.circlePath.cgPath
        loadAnimation.calculationMode = .paced
        loadAnimation.duration = 2.0
        loadAnimation.rotationMode = .rotateAuto
        
        loadAnimation.repeatCount = Float(CGFloat.greatestFiniteMagnitude)
        loader.layer.add(loadAnimation, forKey: "circleAnimation")
    }

}