Loader.swift

protocol Loadable {
    var activityIndicator: UIActivityIndicatorView {get}
    func showLoaderView()
    func hideLoaderView()
}

extension Loadable where Self: UIViewController {
    
    func showLoaderView() {
        activityIndicator.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(activityIndicator)
        activityIndicator.startAnimating()
        
        // Layout
        // ...
    }
    
    func hideLoaderView() {
        activityIndicator.stopAnimating()
        loaderBackgroundView.removeFromSuperview()
    }
}