This code work in SWIFT 2.0.
Must Declare a variable for initialize UIActivityIndicatorView
let actInd: UIActivityIndicatorView = UIActivityIndicatorView()
After initialize put this code in your controller.
actInd.center = ImageView.center
actInd.activityIndicatorViewStyle = UIActivityIndicatorViewStyle.WhiteLarge
view.addSubview(actInd)
actInd.startAnimating()
after your download process complete then hide a animation.
self.actInd.stopAnimating()