Gesture Recognizer Programmatically

override func viewDidLoad() {
    super.viewDidLoad()

    let tap = UITapGestureRecognizer(target: self, action: #selector(doubleTapped))
    tap.numberOfTapsRequired = 2
    view.addGestureRecognizer(tap)
}

@objc func doubleTapped() {
    // do something here
}