Keep autolayout constraints active status on device rotation

Question

I noticed that when I update my autolayout constraints programmatically, all changes are reverted when I rotate the screen.

Reproduce the issue:

• Basic S

Answer 1

You can do the necessary switch with the constraints created via IB for size classes. The trick is to keep the collapsed state in a variable and update constraints as on your button's event as also on trait collection change event.

var collapsed: Bool {
    didSet {
        view.setNeedsUpdateConstraints()
    }
}

@IBAction func onButtonClick(sender: UISwitch) {
    view.layoutIfNeeded()
    collapsed = !collapsed        
    UIView.animate(withDuration: 0.3) {
        view.layoutIfNeeded()
    }
}

override func traitCollectionDidChange(_ previousTraitCollection: UITraitCollection?) {
    super.traitCollectionDidChange(previousTraitCollection)
    view.setNeedsUpdateConstraints()
}

override func updateViewConstraints() {
    constraint1.isActive = !collapsed
    constraint2.isActive = collapsed
    super.updateViewConstraints()
}