title: Event scrolling (scrollViewDidScroll) never called - Swift 3
body: <p>I would like to detect when the user scroll, I used a UIScrollView, I implemented the UIScrollViewDelegate in my ViewController and tried scrollViewDidScroll, scrollViewDidEndScrollingAnimation and all the others but these events are never called.</p>
  
  <pre><code>import UIKit
  class ViewController: UIViewController, UIScrollViewDelegate {     
  
      @IBOutlet weak var scrollView: UIScrollView!    
  
      override func viewDidLoad() {        
          super.viewDidLoad()    
  
          let xOrigin = self.view.frame.width
  
          let view1 = View1(frame: CGRect(x: 0, y: 0, width:self.view.frame.width, height: self.view.frame.height))
          let view2 = View2(frame: CGRect(x: xOrigin, y: 0, width: self.view.frame.width, height: self.view.frame.height))
          let view3 = View3(frame: CGRect(x: xOrigin * 2, y: 0, width: self.view.frame.width, height: self.view.frame.height))
  
          scrollView.addSubview(view1)
          scrollView.addSubview(view2)
          scrollView.addSubview(view3)
  
          self.scrollView.contentSize = CGSize(width: self.view.frame.width * 3, height: self.view.frame.height)
  
          // hide the scrol bar.
          scrollView?.showsHorizontalScrollIndicator = false
      }
  
      override func didReceiveMemoryWarning() {
          super.didReceiveMemoryWarning()
          // Dispose of any resources that can be recreated.
      }
  
  
      func scrollViewDidScroll(_ scrollView: UIScrollView) {
          print("end scroll")
      }
  
  
      func scrollViewDidEndScrollingAnimation(_ scrollView: UIScrollView) {
          print("end scroll")
      }
  }
  </code></pre>