ios - use activity indicator in many VC without duplicating code swift

Question

I have two ViewControllers (A and B) in swift IOS. Both A and B loads data from internet (separately). I want to display activityIndicator while loading. I know I can do it the bad way by declaring it once in each VC as follows

ViewController A

var activityIndicator: UIActivityIndicatorView = UIActivityIndicatorView()

func activityIndicatorBegin() {
    activityIndicator = UIActivityIndicatorView(frame: CGRectMake(0,0,50,50))
    activityIndicator.center = self.view.center
    activityIndicator.hidesWhenStopped = true
    activityIndicator.activityIndicatorViewStyle = UIActivityIndicatorViewStyle.Gray
    view.addSubview(activityIndicator)
    activityIndicator.startAnimating()
    disableUserInteraction()

    greyView = UIView()
    greyView.frame = CGRectMake(0, 0, self.view.bounds.width, self.view.bounds.height)
    greyView.backgroundColor = UIColor.blackColor()
    greyView.alpha = 0.5
    self.view.addSubview(greyView)
}

func activityIndicatorEnd() {
    self.activityIndicator.stopAnimating()
    enableUserInteraction()
    self.greyView.removeFromSuperview()
}

and do the exact same for ViewController B and call the activityIndicatorBegin and activityIndicatorEnd functions that is declared in B view controller. However, I want to make the code cleaner. How could it be done? I am trying to make code cleaner these days.

Thanks,

--UPDATE--

I would imageing something like the following code would work. But it doesnt because I cant declare variables in extensions

    var activityIndicator: UIActivityIndicatorView = UIActivityIndicatorView()

extension UIViewController {
    func activityIndicatorBegin() {
    activityIndicator = UIActivityIndicatorView(frame: CGRectMake(0,0,50,50))
    activityIndicator.center = self.view.center
    activityIndicator.hidesWhenStopped = true
    activityIndicator.activityIndicatorViewStyle = UIActivityIndicatorViewStyle.Gray
    view.addSubview(activityIndicator)
    activityIndicator.startAnimating()
    disableUserInteraction()

    greyView = UIView()
    greyView.frame = CGRectMake(0, 0, self.view.bounds.width, self.view.bounds.height)
    greyView.backgroundColor = UIColor.blackColor()
    greyView.alpha = 0.5
    self.view.addSubview(greyView)
}

func activityIndicatorEnd() {
    self.activityIndicator.stopAnimating()
    enableUserInteraction()
    self.greyView.removeFromSuperview()
    }
}

Answer 1

SWIFT 4

extension UIView{

    func activityStartAnimating(activityColor: UIColor, backgroundColor: UIColor) {
        let backgroundView = UIView()
        backgroundView.frame = CGRect.init(x: 0, y: 0, width: self.bounds.width, height: self.bounds.height)
        backgroundView.backgroundColor = backgroundColor
        backgroundView.tag = 475647
        
        var activityIndicator: UIActivityIndicatorView = UIActivityIndicatorView()
        activityIndicator = UIActivityIndicatorView(frame: CGRect.init(x: 0, y: 0, width: 50, height: 50))
        activityIndicator.center = self.center
        activityIndicator.hidesWhenStopped = true
        activityIndicator.activityIndicatorViewStyle = UIActivityIndicatorViewStyle.gray
        activityIndicator.color = activityColor
        activityIndicator.startAnimating()
        self.isUserInteractionEnabled = false
        
        backgroundView.addSubview(activityIndicator)

        self.addSubview(backgroundView)
    }

    func activityStopAnimating() {
        if let background = viewWithTag(475647){
            background.removeFromSuperview()
        }
        self.isUserInteractionEnabled = true
    }
}

USAGE:

self.view.activityStartAnimating(activityColor: UIColor.white, backgroundColor: UIColor.black.withAlphaComponent(0.5))


self.view.activityStopAnimating()