在Swift中为navigationBar上的UIView设置动画

class CustomView: UIView {
    func animate() {
        UIView.animate(withDuration: 0.5, animations: {
            self.alpha = 0.0
        }) { (finished) in
            UIView.animate(withDuration: 0.5, animations: {
                self.alpha = 1.0
            })
        }
    }
}

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        let customView = CustomView(frame: CGRect(x: 0, y: 0, width: 100, height: 100))
        customView.backgroundColor = .red
        
        if let navigationBar = self.navigationController?.navigationBar {
            navigationBar.addSubview(customView)
        }
        
        customView.animate()
    }
}