[iOS/Swift] Animate adjusting scroll view top inset via UIViewController.additionalSafeAreaInsets

ViewController.swift

class ViewController: UIViewController {

  @IBOutlet weak var textView: UITextView!
  
  override func viewDidLoad() {
    super.viewDidLoad()
    
    textView.contentInsetAdjustmentBehavior = .always
    textView.delegate = self
  }
  
  var lastContentOffset: CGPoint?
  
  var shouldAddInsets = false
  @IBAction func buttonDidTap(_ sender: Any) {
    lastContentOffset = self.textView.contentOffset
    additionalSafeAreaInsets.top = self.shouldAddInsets ? 100 : 0
    shouldAddInsets.toggle()
  }
}

extension ViewController: UITextViewDelegate {
  func scrollViewDidChangeAdjustedContentInset(_ scrollView: UIScrollView) {
    if let lastContentOffset {
      scrollView.setContentOffset(lastContentOffset, animated: false)
      UIView.animate(withDuration: 0.2) {
        scrollView.contentOffset.y = -scrollView.adjustedContentInset.top
      }
    }
  }
}