Line up CenterYAnchor of UIButton to UIPageControl Swift

Question

I have some code where I'm adding in a "close" UIButton to the UIPageController.view, and that works great.

WORKING CODE:

class func closeButton(_ pageController: UIPageViewController) -> UIButton {

    let button = UIButton()

    button.setTitleColor(UIColor.white, for: UIControlState())
    button.setTitle("Close", for: UIControlState())
    button.titleLabel!.font = UIFont.systemFont(ofSize: 15)
    button.contentHorizontalAlignment = UIControlContentHorizontalAlignment.left
    button.translatesAutoresizingMaskIntoConstraints = false

    pageController.view.addSubview(button)

    button.widthAnchor.constraint(equalToConstant: 50).isActive = true
    button.heightAnchor.constraint(equalToConstant: 36).isActive = true
    button.trailingAnchor.constraint(equalTo: pageController.view.trailingAnchor).isActive = true
    button.bottomAnchor.constraint(equalTo: pageController.view.bottomAnchor).isActive = true

    return button
}

But then I tested my code on the iPhone X Simulator, and the UIPageControl is much higher from the bottom than the other iPhones. So now that close button I just added is in the bottom rounded corner and the UIPageControl is much higher.

So then I tried referencing the the UIPageControl with:

let pageControl: UIPageControl = UIPageControl.appearance()

And then replace the button.bottomAnchor.constraint... with:

button.centerYAnchor.constraint(equalTo: pageControl.centerYAnchor).isActive = true

But this causes an error to be thrown. I tried printing the UIPageControl.frame and it is 0,0,0,0. So I'm assuming that has something to do with it.

Is there a way to make a constraint against the UIPageControl?

Answer 1

If you are using a custom view try to update your constraint in layoutSubviews() method, or in viewDidLayoutSubviews() method of your view controller:

func layoutSubviews() {
    super.layoutSubviews()
    button.centerYAnchor.constraint(equalTo: pageControl.centerYAnchor).isActive = true
}