UIView animation works one time then it doesn't work

Question

I am trying to do an animation for my view but it just works the first time which is isOpen = true. It works but when I call my function again isOpen = false, nothing changes.

Parent view is self (UIView). Child is label (UILabel).

private func expansionView(isOpen: Bool) {
    if isOpen {
        label.backgroundColor = .white
        NSLayoutConstraint.activate([
             label.centerYAnchor.constraint(equalTo: self.topAnchor),
             label.leadingAnchor.constraint(equalTo: self.leadingAnchor, constant: 15),
         ])
        
        UIView.animate(withDuration: 1, animations: {
            self.layoutIfNeeded()
        }) { (_) in
            
        }
    } else {
        label.backgroundColor = .clear
        NSLayoutConstraint.activate([
             label.centerYAnchor.constraint(equalTo: self.centerYAnchor),
             label.leadingAnchor.constraint(equalTo: self.leadingAnchor , constant: 15),
         ])

        UIView.animate(withDuration: 1, animations: {
            self.layoutIfNeeded()
        }) { (_) in
            print("Animation Completed!!!")
        }
    }
}

Answer 1

You need to have two constraints to make one of them active. You can also animate changing label's background color to clear. And you can simplify your function like below.

// define both vertical constraints
var constraintToCenterYAnchor: NSLayoutConstraint!
var constraintToTopAnchor: NSLayoutConstraint!

// where you init your view..
init() {
    // init your constraints
    constraintToTopAnchor = label.centerYAnchor.constraint(equalTo: topAnchor)
    constraintToCenterYAnchor = label.centerYAnchor.constraint(equalTo: centerYAnchor)

    // set and activate other constraints once.
    label.leadingAnchor.constraint(equalTo: leadingAnchor, constant: 15).isActive = true

    // update background color of the label
    label.backgroundColor = .clear
    label.layer.backgroundColor = UIColor.white.cgColor
}

// simplify your function
private func expansionView(_ isOpen: Bool) {
    constraintToTopAnchor.isActive = isOpen
    constraintToCenterYAnchor.isActive = !isOpen
    
    UIView.animate(withDuration: 1) {
        self.label.layer.opacity = isOpen ? 1.0 : 0.0
        self.layoutIfNeeded()
    }
}