UIScrollView's origin changes after popping back to the UIViewController

Question

I have a UIViewController subclass as a scene in the storyboard that contains a UIScrollView containing various subviews. One of the subviews is a

Answer 1

I used a combination of the different solutions posted everywhere on SO, and came up with this subclass:

// Keeps track of the recent content offset to be able to restore the
// scroll position when a modal viewcontroller is dismissed
class ScrollViewWithPersistentScrollPosition: UIScrollView {

    // The recent content offset for restoration.
    private var recentContentOffset: CGPoint = CGPoint(x: 0, y: 0)

    override func willMove(toWindow newWindow: UIWindow?) {
        if newWindow != nil {
            // save the scroll offset.
            self.recentContentOffset = self.contentOffset
        }
        super.willMove(toWindow: newWindow)
    }

    override func didMoveToWindow() {
        if self.window != nil {
            // restore the offset.
            DispatchQueue.main.async(execute: {
                // restore it
                self.contentOffset = self.recentContentOffset
            })
        }
        super.didMoveToWindow()
    }
 }

Tested on iOS 11.2 / Xcode 9.2.