How to change the layout margins programmatically

Question

I have very easy setup in viewDidLoad, just add a view and pin it to superview's margins by 'anchors' style:

let myView = UIView(frame: .zero)
myView.translatesAutoresizingMaskIntoConstraints = false
view.addSubview(myView)
myView.backgroundColor = UIColor.red
myView.leadingAnchor.constraint(equalTo: view.layoutMarginsGuide.leadingAnchor).isActive = true
myView.trailingAnchor.constraint(equalTo: view.layoutMarginsGuide.trailingAnchor).isActive = true
myView.bottomAnchor.constraint(equalTo: view.layoutMarginsGuide.bottomAnchor).isActive = true
myView.topAnchor.constraint(equalTo: view.layoutMarginsGuide.topAnchor).isActive = true
view.layoutMargins = .zero

The problem is that there is still a margin when running this in simulator. Why layoutMargins zeroing is ignored?

Answer 1

You need add this in your UIViewController viewWillLayoutSubviews() method

override func viewWillLayoutSubviews() {
    super.viewWillLayoutSubviews()
    view.layoutMargins = .zero
    view.layoutMarginsDidChange()
}

but if you need .zero of margins you can as I said in my comments use view.leadingAnchor as well

Answer 2

Try this.

if #available(iOS 11, *) {
   viewRespectsSystemMinimumLayoutMargins = false
   view.layoutMargins = UIEdgeInsets(top: 0, left: 8, bottom: 0, right: 0)
}

Apple document for reference.