changing the multiplier value of a constraint - swift

Question

I have a menu bar which sits at the top of a CollectionViewController with several different titles about 30 pixels high
. Each title has a small bar underneath, indicating which page/item the user is on, similar to the Youtube app.
class MenuBar : UIView {
var menuSectionTitles = ["Title1","Title2", "Title3","Title4"]
var numberOfSectionsInHorizontalBar : CGFloat?
var horizontalBarLeftAnchorConstraint: NSLayoutConstraint?
var horizontalBarWidthAnchorConstraint: NSLayoutConstraint?
override init(frame: CGRect) {
super.init(frame: frame)
setupHorizontalBar()
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
func setupHorizontalBar() {
let horizontalBarView = UIView()
horizontalBarView.backgroundColor = UIColor.rgb(10, green: 150, blue: 255)
horizontalBarView.translatesAutoresizingMaskIntoConstraints = false
addSubview(horizontalBarView)
horizontalBarLeftAnchorConstraint = horizontalBarView.leftAnchor.constraint(equalTo: self.leftAnchor)
horizontalBarLeftAnchorConstraint?.isActive = true
horizontalBarView.bottomAnchor.constraint(equalTo: self.bottomAnchor).isActive = true
// Set the multiplier/width of the horizontal bar to indicate which page the user is on
horizontalBarWidthAnchorConstraint = horizontalBarView.widthAnchor.constraint(equalTo: widthAnchor, multiplier: 1 / 4)
horizontalBarWidthAnchorConstraint?.isActive = true
horizontalBarView.heightAnchor.constraint(equalToConstant: 3).isActive = true
}
}
The multiplier value for horizontalBarWidthAnchorConstraint is hard coded in at a value of 1/4
I want to reuse the view multiple times across different view controllers, therefore have attempted to change the multiplier of the horizontalBarWidthAnchorConstraint like so:
class ViewController: UICollectionViewController {
lazy var menuBar : MenuBar = {
let mb = OptionsBar()
mb.menuOptions = ["Title1", "Title2", "Title3"]
mb.translatesAutoresizingMaskIntoConstraints = false
mb.horizontalBarWidthAnchorConstraint?.constant = 1/3
return mb
}()
}
But this method does not work. I can not find a way to change the multiplier value from inside the ViewController.

Answer 1

In the code here you are changing the constant of the constraint, not the multiplier. Is that correct?
Also note, the multiplier of a constraint is read only. You cannot change it. If you want to change the multiplier of a constraint applying to a view then the only to do it is to add a new constraint with the new multiplier and remove the old constraint.
The only part of a constraint that is read/write is the constant property.