Loading an "overlay" when running long tasks in iOS

The above answers add a loading view but it doesn't block click events on the screen also it does not provides overlay for rest of screen. You can achieve it as follows:

let alert = UIAlertController(title: nil, message: "Please wait...", preferredStyle: .Alert)alert.view.tintColor = UIColor.blackColor()let loadingIndicator: UIActivityIndicatorView = UIActivityIndicatorView(frame: CGRectMake(10, 5, 50, 50)) as UIActivityIndicatorViewloadingIndicator.hidesWhenStopped = trueloadingIndicator.activityIndicatorViewStyle = UIActivityIndicatorViewStyle.GrayloadingIndicator.startAnimating();alert.view.addSubview(loadingIndicator)presentViewController(alert, animated: true, completion: nil)

Swift 3.0

let alert = UIAlertController(title: nil, message: "Please wait...", preferredStyle: .alert)let loadingIndicator = UIActivityIndicatorView(frame: CGRect(x: 10, y: 5, width: 50, height: 50))loadingIndicator.hidesWhenStopped = trueloadingIndicator.activityIndicatorViewStyle = UIActivityIndicatorViewStyle.grayloadingIndicator.startAnimating();alert.view.addSubview(loadingIndicator)present(alert, animated: true, completion: nil)

Swift 4.0 and newer

let alert = UIAlertController(title: nil, message: "Please wait...", preferredStyle: .alert)let loadingIndicator = UIActivityIndicatorView(frame: CGRect(x: 10, y: 5, width: 50, height: 50))loadingIndicator.hidesWhenStopped = trueloadingIndicator.style = UIActivityIndicatorView.Style.grayloadingIndicator.startAnimating();alert.view.addSubview(loadingIndicator)present(alert, animated: true, completion: nil)

and you can hide it as follows:

dismiss(animated: false, completion: nil)

It will be shown as follows:

Just create yourself an overlay view, which you add to your parent view and remove it once your task is done, e.g. to add it:

var overlay : UIView? // This should be a class variable[ ... ]overlay = UIView(frame: view.frame)overlay!.backgroundColor = UIColor.blackColor()overlay!.alpha = 0.8view.addSubview(overlay!)

For removal:

overlay?.removeFromSuperview()

Blur background + Activity Indicator, Swift 5 example

extension UIView {    func showBlurLoader() {        let blurLoader = BlurLoader(frame: frame)        self.addSubview(blurLoader)    }    func removeBluerLoader() {        if let blurLoader = subviews.first(where: { $0 is BlurLoader }) {            blurLoader.removeFromSuperview()        }    }}class BlurLoader: UIView {    var blurEffectView: UIVisualEffectView?    override init(frame: CGRect) {        let blurEffect = UIBlurEffect(style: .dark)        let blurEffectView = UIVisualEffectView(effect: blurEffect)        blurEffectView.frame = frame        blurEffectView.autoresizingMask = [.flexibleWidth, .flexibleHeight]        self.blurEffectView = blurEffectView        super.init(frame: frame)        addSubview(blurEffectView)        addLoader()    }    required init?(coder aDecoder: NSCoder) {        fatalError("init(coder:) has not been implemented")    }    private func addLoader() {        guard let blurEffectView = blurEffectView else { return }        let activityIndicator = UIActivityIndicatorView(style: .whiteLarge)        activityIndicator.frame = CGRect(x: 0, y: 0, width: 50, height: 50)        blurEffectView.contentView.addSubview(activityIndicator)        activityIndicator.center = blurEffectView.contentView.center        activityIndicator.startAnimating()    }}