ViewController.swift

final class ViewController: UIViewController {
    @IBOutlet weak var scrollView: UIScrollView!
    private var keyboardObserver: KeyboardObserver?
    
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        keyboardObserver = KeyboardObserver(changeHandler: { [weak self] (info) in
            guard let self = self else { return }
            switch info.event {
            case .willShow:
                self.scrollView.contentInset.bottom = info.endFrame.height
            case .willHide:
                self.scrollView.contentInset.bottom = 0
            default:
                break
            }
        })
    }
    
    override func viewDidDisappear(_ animated: Bool) {
        super.viewDidDisappear(animated)
        keyboardObserver = nil
    }
}