Unexpected behaviour of autolayout when isScrollEnabled of TextView is set to false - swift

Question

I'm trying to make growing textview and make it scrollable at some content size. What i'm doing is:
func textViewDidChange(_ textView: UITextView) {
if textView.contentSize.height > 100 && !textView.isScrollEnabled {
let frame = textView.frame
textView.isScrollEnabled = true
let heightConstraint: NSLayoutConstraint = .init(item: textView, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: frame.height)
heightConstraint.identifier = "height"
textView.addConstraint(heightConstraint)
}
if textView.contentSize.height < 100 && textView.isScrollEnabled {
textView.isScrollEnabled = false
let heightConstraint = textView.constraints.first { constraint in
constraint.identifier == "height"
}
textView.removeConstraint(heightConstraint!)
}
print(textView.contentSize.height, textView.frame.height)
}
if content size is greater than 100 i enable the scroll and add constraint for height
if content size is less than 100 i disable the scroll and remove the constraint (i expect that textview to fit to its content, as it usually does when scroll is disabled)
i have no problems with enabling the scroll, but when contentsize becomes less than 100, the second if statement fires and the textview for some reason takes the whole screen space. when i call textViewDidChange again (by deleting or adding smth to textview) both ifs fire and everything works as it should be.
what i tried to do is to call textview.sizeToFit() and view.layoutIfNeeded() but had no success. what am i doing wrong here?

Answer 1

I think you're doing a lot more than you need to do.
A better approach would be to create the Height constraint, equal to a constant value of 100, and then activate/de-activate it as needed.
Try it like this:
class ViewController: UIViewController, UITextViewDelegate {
let myTextView = UITextView()
var tvHeightConstraint: NSLayoutConstraint!
override func viewDidLoad() {
super.viewDidLoad()
myTextView.translatesAutoresizingMaskIntoConstraints = false
myTextView.font = .systemFont(ofSize: 18.0)
myTextView.backgroundColor = .yellow
view.addSubview(myTextView)
let g = view.safeAreaLayoutGuide
tvHeightConstraint = myTextView.heightAnchor.constraint(equalToConstant: 100.0)
NSLayoutConstraint.activate([
myTextView.topAnchor.constraint(equalTo: g.topAnchor, constant: 40.0),
myTextView.leadingAnchor.constraint(equalTo: g.leadingAnchor, constant: 40.0),
myTextView.trailingAnchor.constraint(equalTo: g.trailingAnchor, constant: -40.0),
])
myTextView.isScrollEnabled = false
myTextView.delegate = self
}
func textViewDidChange(_ textView: UITextView) {
textView.isScrollEnabled = (textView.contentSize.height > 100)
tvHeightConstraint.isActive = textView.isScrollEnabled
}
}