scrollViewDidScroll not getting called (I set the delegate!)

Situation: I am creating an imageGallery which is a viewController that I am presenting modally. I have created it all programatically, I haven't touched the storyboard. The viewController has a scrollView that contains ImageViews, which each hold an image. I have set scrollView.isPagingEnabled = true and it works as expected, I can scroll through the images fine.

Issue: I am trying to do some work when the scrollView has scrolled. I have set the delegate (which seems to be the main issue people have had when I searched for an answer) but scrollViewDidScroll never gets called. I'm completely at a loss for what is happening.I've tried quite a lot of different things, but have now run out of ideas

@objc public class ImageGallery: UIViewController, UIScrollViewDelegate {

// MARK:- VARIABLES

/// An array of imageItems
@objc public var galleryItems = [ImageGalleryItem]()

/// The index of the image the gallery should start at
@objc public var startingIndex: NSNumber?

/// The UIImage to display if there is an error
@objc public var errorImage: UIImage?

/// The UIImage to display if the ImageGalleryItem doesn't have an image
@objc public var defaultImage: UIImage?

var scrollView: UIScrollView!

// MARK:- INITS

/// Initialiser for ImageGallery passing an array of ImageGalleryItems
///
/// - Parameter ImageGalleryItems: an array of ImageGalleryItems
@objc public init() {

    self.defaultImage = UIImage(named: "default", in: getResourceBundle(), compatibleWith: nil)!
    self.errorImage = UIImage(named: "error", in: getResourceBundle(), compatibleWith: nil)!
    super.init(nibName:nil, bundle:nil)
}


@objc public required init?(coder aDecoder: NSCoder) {
    super.init(coder: aDecoder);
}


// MARK:- VIEW LIFECYCLES
override public func viewDidLoad() {

    super.viewDidLoad()

    configureScrollView()

    self.scrollView.delegate = self
    configureImageViews()
    configurePresentationDefaults()
}


func configureScrollView() {

    self.scrollView = UIScrollView(frame: view.frame)

    self.scrollView.isPagingEnabled = true
    self.scrollView.contentOffset = CGPoint(x: CGFloat(truncating: startingIndex ?? 0) * UIScreen.main.bounds.width, y: 0)

    let imagesCount = galleryItems.count
        let contentWidth = CGFloat(imagesCount) * UIScreen.main.bounds.width
        self.scrollView.contentSize = CGSize(width: contentWidth, height: UIScreen.main.bounds.height)


    if let toolbar = configureToolBar() {

        view.addSubview(self.scrollView)
        view.addSubview(toolbar)
        view.bringSubviewToFront(toolbar)
    }
}

private func scrollViewDidScroll(_ scrollView: UIScrollView) {
    print("delegate")
}

Update

I was missing an !

private func scrollViewDidScroll(_ scrollView: UIScrollView!) {
    print("delegate")
}

Did the trick.

Function signature should not be private to match with delegate implementation:

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    print("delegate")
}

Solved the issue.