Adding a subviews than can change each constraint

A few observations:

1. As Geoff Hackworth pointed out, you are creating only one subview (one that was instantiated once with a closure). You really want to have a method that creates a new subview every time.

2. In the else block, you are setting the top anchor of every subsequent view to be the top anchor of the preceding view. You presumably wanted to set the next view’s top anchor to be relative to the preceding view’s bottom anchor.

3. As a minor detail, you are not setting the bottom anchor of the last view. Generally we want our constraints to be fully defined, so I would suggest adding a bottomAnchor for the last subview. This is especially true in self-sizing cells, that need an unambiguous set of vertical constraints.

So, perhaps:

func createView() -> UIView {
    let view = UIView()
    view.backgroundColor = .red
    view.translatesAutoresizingMaskIntoConstraints = false
    return view
}

func addSubviews() {
    var topAnchor: NSLayoutYAxisAnchor = view.safeAreaLayoutGuide.topAnchor
    var subview: UIView!
    for index in 1...11 {
        subview = createView()
        view.addSubview(subview)
        subview.activateAnchors(top: topAnchor, xCenter: view.centerXAnchor, paddingTop: 10, width: 50, height: 50)
        topAnchor = subview.bottomAnchor
    }
    view.activateAnchors(bottom: subview.bottomAnchor, paddingBottom: 10)
}

And, if you forgive me, I tweaked the UIView extension:

extension UIView{
    func activateAnchors(
        top: NSLayoutYAxisAnchor? = nil,
        bottom: NSLayoutYAxisAnchor? = nil,
        leading: NSLayoutXAxisAnchor? = nil,
        trailing: NSLayoutXAxisAnchor? = nil,
        xCenter: NSLayoutXAxisAnchor? = nil,
        yCenter: NSLayoutYAxisAnchor? = nil,
        paddingTop: CGFloat = 0,
        paddingBottom: CGFloat = 0,
        paddingLeft: CGFloat = 0,
        paddingRight: CGFloat = 0,
        width: CGFloat? = nil,
        height: CGFloat? = nil
    ) {
        if let top {
            topAnchor.constraint(equalTo: top, constant: paddingTop).isActive = true
        }
        if let bottom {
            bottomAnchor.constraint(equalTo: bottom, constant: paddingBottom).isActive = true
        }
        if let leading {
            leadingAnchor.constraint(equalTo: leading, constant: paddingLeft).isActive = true
        }
        if let trailing {
            trailingAnchor.constraint(equalTo: trailing, constant: paddingRight).isActive = true
        }
        if let xCenter {
            centerXAnchor.constraint(equalTo: xCenter).isActive = true
        }
        if let yCenter {
            centerYAnchor.constraint(equalTo: yCenter).isActive = true
        }
        if let width {
            widthAnchor.constraint(equalToConstant: width).isActive = true
        }
        if let height {
            heightAnchor.constraint(equalToConstant: height).isActive = true
        }
    }
}

In the above, I have also:

1. Simplified the for loop so we do not need the if-else based upon the counter.

2. I have given the UIView extension default values for its parameters, so you do not need to supply parameters of nil at the call point.

Needless to say, we often would consider a UIStackView:

func addSubviews() {
    let subviews = (1...11).map { _ in createView() } 

    let stackView = UIStackView(arrangedSubviews: subviews)
    stackView.translatesAutoresizingMaskIntoConstraints = false
    stackView.alignment = .center
    stackView.axis = .vertical
    stackView.spacing = 10
    view.addSubview(stackView)

    stackView.activateAnchors(top: view.topAnchor, bottom: view.bottomAnchor, xCenter: view.centerXAnchor, paddingTop: 10, paddingBottom: -10)
    subviews.forEach { $0.activateAnchors(width: 50, height: 50) }
}

That having been said, stack views within cells don’t always work perfectly, so you might have to resort to the prior technique.