UIScrollView as UIControl

Question

I am implementing a UIControl using UIScrollView. I wish to send .valueChanged event when user scrolls the scroll view with finger, not otherwise. To do this, I need to compare the currentValue I compute when the scrolling happens, and if it is different than previous value, I send a .valueChanged event via sendActionsForControlEvents API. My questions:

(a) What is the most reliable way in all cases to know that user dragged the scroll view(scrolling can also happen in my code using automated API) -- scrollView.isDragging or scrollView.isTracking, or both?

(b) What is the way to notice change in currentValue (without storing previous value)? I am doing this using Swift 4 but it doesn't seems to give old value:

 private(set) public var currentValue = Int(0) {
    willSet (newValue) {
        NSLog("Old value \(currentValue), new \(newValue)")
    }
 }

Answer 1

From the comments using delegates I believe the solid solution should look something similar to:

class MyClass: NSObject, UIScrollViewDelegate {

    private var isUserDragging: Bool = false

    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        if isUserDragging {
            // Should trigger only when scroll view visible frame changes and user is dragging
            print("User is dragging")
        }
    }

    func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
        isUserDragging = true // Should only be called when user starts dragging
    }

    func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
        if decelerate == false {
            isUserDragging = false // Disable user dragging only if no deceleration will be performed
        }
    }

    func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
        isUserDragging = false // When deceleration is done user is not dragging anymore
    }

}

Now you should be able to get your event within scrollViewDidScroll.