Detecting UIScrollView page change

Question

Is there a way to detect or get a notification when user changes the page in a paging-enabled UIScrollView?

Answer 1

How about combining two methods of UIScrollViewDelegate?

In scrollViewDidEndDragging(_:willDecelerate:), if it stops right away, we do the page calculation; if it is decelerating, we let it go and it will be caught by scrollViewDidEndDecelerating(_:).

The code is tested with XCode version 7.1.1, Swift version 2.1

class ViewController: UIViewController, UIScrollViewDelegate {

  // MARK: UIScrollViewDelegate
  func scrollViewDidEndDragging(scrollView: UIScrollView, willDecelerate decelerate: Bool) {
    if decelerate == false {
        let currentPage = scrollView.currentPage
        // Do something with your page update
        print("scrollViewDidEndDragging: \(currentPage)")
    }
  }

  func scrollViewDidEndDecelerating(scrollView: UIScrollView) {
    let currentPage = scrollView.currentPage
    // Do something with your page update
    print("scrollViewDidEndDecelerating: \(currentPage)")
  }

}

extension UIScrollView {
   var currentPage: Int {
      return Int((self.contentOffset.x+ (0.5*self.frame.size.width))/self.frame.width)+1
   }
}