Spinner indicator to put over loading views

UIViewControllerExtension.swift

extension UIViewController {
    func displaySpinner(onView : UIView) -> UIView {
        let spinnerView = UIView.init(frame: onView.bounds)
        spinnerView.backgroundColor = UIColor.white //UIColor.black.withAlphaComponent(0.5)
        let ai = UIActivityIndicatorView(style: .gray)
        ai.startAnimating()
        ai.center = spinnerView.center
        
        DispatchQueue.main.async {
            spinnerView.addSubview(ai)
            onView.addSubview(spinnerView)
        }
        
        return spinnerView
    }
    
    func removeSpinner(spinner :UIView) {
        DispatchQueue.main.async {
            spinner.removeFromSuperview()
        }
    }
}