let label = UILabel()
label.translatesAutoresizingMaskIntoConstraints = false
label.backgroundColor = UIColor.greenColor()
label.text = "Hello, World"
label.sizeToFit()
view.addSubview(label)
label.leadingAnchor.constraintEqualToAnchor(
view.readableContentGuide.leadingAnchor).active = true
label.topAnchor.constraintEqualToAnchor(
view.readableContentGuide.topAnchor).active = true
label.trailingAnchor.constraintEqualToAnchor(
view.readableContentGuide.trailingAnchor).active = true
label.bottomAnchor.constraintEqualToAnchor(
view.readableContentGuide.bottomAnchor).active = trueThe above examples is from "iOS 9 Swift Programming Cookbook".