Updating layout anchors not working as expected - ios

Question

I have created a view with height 100 using NSLayout anchors. When I'm trying to update that on button click, it's not working.
I have tried below code, but it's not working.
class ViewController: UIViewController {
#IBOutlet weak var button: UIButton!
let viewAnimate = UIView()
var isHidden = false
override func viewDidLoad() {
super.viewDidLoad()
view.addSubview(viewAnimate)
}
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
viewAnimate.translatesAutoresizingMaskIntoConstraints = false
viewAnimate.leadingAnchor.constraint(equalTo: self.view.leadingAnchor, constant: 8).isActive = true
viewAnimate.trailingAnchor.constraint(equalTo: self.view.trailingAnchor, constant: -8).isActive = true
viewAnimate.topAnchor.constraint(equalTo: self.view.topAnchor, constant: 100).isActive = true
viewAnimate.heightAnchor.constraint(equalToConstant: 100).isActive = true
viewAnimate.backgroundColor = UIColor.red
}
#IBAction func show() {
if !isHidden {
viewAnimate.topAnchor.constraint(equalTo: self.view.topAnchor, constant: 200).isActive = true
button.setTitle("Show", for: .normal)
} else {
button.setTitle("Hide", for: .normal)
viewAnimate.topAnchor.constraint(equalTo: self.view.topAnchor, constant: 100).isActive = true
}
UIView.animate(withDuration: 1) {
self.viewAnimate.layoutIfNeeded()
}
isHidden = !isHidden
}
}
View should change the height based on height constraint

Answer 1

Your current code creates conflicts as every line like viewAnimate.topAnchor.constraint(equalTo: adds a new constraint , create a var
var topCon:NSLayoutConstraint!
topCon = viewAnimate.topAnchor.constraint(equalTo: self.view.topAnchor, constant: 100)
topCon.isActive = true
#IBAction func show() {
if !isHidden {
topCon.constant = 200
button.setTitle("Show", for: .normal)
} else {
button.setTitle("Hide", for: .normal)
topCon.constant = 100
}
UIView.animate(withDuration: 1) {
self.view.layoutIfNeeded()
}
isHidden = !isHidden
}