显示模态视图控制器时的黑色背景

当我看到我的视图呈现为黑色背景色时,我有一个问题。这是我的代码:

class Loader: UIViewController, NVActivityIndicatorViewable {

override func viewDidLoad() {
    super.viewDidLoad()
    self.modalPresentationStyle = .currentContext
    self.view.backgroundColor = .clear
    self.view.isOpaque = false
    let width = UIScreen.main.bounds.width
    let height = UIScreen.main.bounds.height
    let frame = CGRect(x: width / 2, y: height / 2, width: 100, height: 100)
    let activityIndicatorView = NVActivityIndicatorView(frame: frame, type: NVActivityIndicatorType.lineScale, color: GlobalVariables.stacksBlue, padding: 20)
    self.view.addSubview(activityIndicatorView)
    activityIndicatorView.startAnimating()
    activityIndicatorView.translatesAutoresizingMaskIntoConstraints = false
    activityIndicatorView.centerXAnchor.constraint(equalTo: view.centerXAnchor).isActive = true
    activityIndicatorView.centerYAnchor.constraint(equalTo: view.centerYAnchor).isActive = true
}

其中的扩展名是call函数:

extension UIViewController {
func showLoader() {
    let loader = Loader()
    self.modalPresentationStyle = .currentContext
    self.present(loader, animated: false, completion: nil)
}
func hideLoader() {
    self.dismiss(animated: false, completion: nil)
}

}