heightAnchor.constraint not change height of view - swift

Question

I use this code:
func show(){
view.translatesAutoresizingMaskIntoConstraints = false
view.leftAnchor.constraint(equalTo: view.leftAnchor, constant: 0).isActive = true
view.topAnchor.constraint(equalTo: view.topAnchor, constant: 0).isActive = true
view.heightAnchor.constraint(equalToConstant: view.frame.height - 300).isActive = true
view.rightAnchor.constraint(equalTo: view.rightAnchor, constant: 0).isActive = true
}
func hide(){
view.translatesAutoresizingMaskIntoConstraints = false
view.leftAnchor.constraint(equalTo: view.leftAnchor, constant: 0).isActive = true
view.topAnchor.constraint(equalTo: view.topAnchor, constant: 0).isActive = true
view.heightAnchor.constraint(equalToConstant: view.frame.height + 300).isActive = true
view.rightAnchor.constraint(equalTo: view.rightAnchor, constant: 0).isActive = true
}
show function works fine, but hide function does not work and heightAnchor does not work.

Answer 1

First declare constraints
var heightArchonWhenShow = view.heightAnchor.constraint(equalToConstant: view.frame.height - 300)
var heightArchonWhenHide = view.heightAnchor.constraint(equalToConstant: view.frame.height + 300)
After init your constraints on ViewDidLoad
func setConstraints(){
view.translatesAutoresizingMaskIntoConstraints = false
view.leftAnchor.constraint(equalTo: view.leftAnchor, constant: 0).isActive = true
view.topAnchor.constraint(equalTo: view.topAnchor, constant: 0).isActive = true
view.rightAnchor.constraint(equalTo: view.rightAnchor, constant: 0).isActive = true
heightArchonWhenShow.isActive = true
}
And simple active them , don't overwrite. Like this:
func show(){
heightArchonWhenShow.isActive = true
heightArchonWhenHide.isActive = false
}
func hide(){
heightArchonWhenShow.isActive = false
heightArchonWhenHide.isActive = true
}
If u want u can also animate changes, like that :
func hide(){
heightArchonWhenShow.isActive = false
heightArchonWhenHide.isActive = true
UIView.animate(withDuration: 0.3) {
self.view.layoutIfNeeded()
}
}

Answer 2

I recommend you to setup your constraint in a different function like maybe setup() and store them in some variable that you can modify after, I'll show you an example
var constraint: NSLayoutConstraint?
func setup() {
constraint = view.heightAnchor.constraint(equalToConstant: view.frame.height)
}
func show() {
if constraint != nil {
constraint!.constant = constraint!.constant + 300
}
}
func hide() {
if constraint != nil {
constraint!.constant = constraint!.constant - 300
}
}

Answer 3

You need only 1 var
var heightCon = view.heightAnchor.constraint(equalToConstant: view.frame.height - 300)
heightCon.isActive = true
Then manage it's constant value
func showOrHide(_ te:Bool){
heightCon.constant = te ? view.frame.height - 300 : view.frame.height + 300
UIView.animate(withDuration: 0.3) {
self.view.layoutIfNeeded()
}
}