如何在自定义视图中以编程方式添加UIActivityIndicator？

import UIKit

let activityIndicator = UIActivityIndicatorView(style: .gray)
activityIndicator.center = CGPoint(x: customView.bounds.width / 2, y: customView.bounds.height / 2)

customView.addSubview(activityIndicator)

activityIndicator.startAnimating() // 开始动画
activityIndicator.stopAnimating() // 停止动画

import UIKit

class CustomView: UIView {
    private let activityIndicator = UIActivityIndicatorView(style: .gray)
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        setupActivityIndicator()
    }
    
    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        setupActivityIndicator()
    }
    
    private func setupActivityIndicator() {
        activityIndicator.center = CGPoint(x: bounds.width / 2, y: bounds.height / 2)
        addSubview(activityIndicator)
    }
    
    func startLoading() {
        activityIndicator.startAnimating()
    }
    
    func stopLoading() {
        activityIndicator.stopAnimating()
    }
}