UITextView that starts scrolling when text reached N lines - ios

Question

I'm start implementing text input to a chat app and wondering that is standard behavior of a UITextView with scroll enabled absolutely does not meet expectations.
I want just it is done in chats like WhatsApp. When text reached N, 5 for example lines, scroll bar appear and text container starts scrolling. I wrote code like this, but it doesn't work.
As i think needs to count rows in text container and make content insets, or something like this.
func textViewDidChange(_ textView: UITextView) {
let fixedWidth = myTextView.frame.size.width
myTextView.sizeThatFits(CGSize(width: fixedWidth, height: CGFloat.greatestFiniteMagnitude))
let newSize = myTextView.sizeThatFits(CGSize(width: fixedWidth, height: CGFloat.greatestFiniteMagnitude))
var newFrame = myTextView.frame
let oldFrame = myTextView.frame
newFrame.size = CGSize(width: max(newSize.width, fixedWidth), height: newSize.height)
myTextView.frame = newFrame
let shift = oldFrame.height - newFrame.height
textView.contentInset = UIEdgeInsets(top: 0, left: 0, bottom: shift, right: 0)
textView.scrollIndicatorInsets = textView.contentInset
textView.scrollRangeToVisible(textView.selectedRange)
}
And myTextView is specified as:
let myTextView : UITextView = {
let textView = UITextView()
textView.translatesAutoresizingMaskIntoConstraints = false
textView.isScrollEnabled = false
textView.textContainer.maximumNumberOfLines = 5
textView.textContainer.lineBreakMode = .byWordWrapping
textView.inputAccessoryView = UIView()
return textView
}()

Answer 1

Not based on number of lines, but on a user defined height. You'll find your answer here:
https://stackoverflow.com/a/51235517/10115072

Answer 2

If you want this behaviour to happen is simple:
Create a UIView having UITextView inside
Create a height constraint in UIView priority 1000 of less than or equal your MAX_HEIGHT and also greater than or equal you MIN_HEIGHT
Create a height constraint in you TextView priority 999 equal to your MIN_HEIGHT
Then add this code to your controller
Code:
class YourViewController: KUIViewController {
#IBOutlet weak var textView: UITextView!
override func viewDidLoad() {
super.viewDidLoad()
textView.delegate = self
textView.isScrollEnabled = true
}
}
extension YourViewController: UITextViewDelegate {
func textViewDidChange(_ textView: UITextView) {
let size = CGSize(width: view.frame.width, height: .infinity)
let estimatedSize = textView.sizeThatFits(size)
textView.constraints.forEach { (constraint) in
if constraint.firstAttribute == .height {
constraint.constant = estimatedSize.height
}
}
}
}
This has the same behaviour as WhatsApp textView