如何在Swift中使用多行文字将UILabel居中?

我想通过编程将一个带有多行文本的标签居中。我已将其添加到以下约束中,但它仅显示在一行上!我怎么能让它显示多行而不超过屏幕的边界?

let noResults = UILabel()

noResults.text = self.emptyMessage
noResults.lineBreakMode = .byWordWrapping

noResults.minimumScaleFactor = 0.5
noResults.textAlignment = .center
noResults.font = UIFont(name: "Montserrat-Light", size: 20.0)!
noResults.numberOfLines = 0
noResults.adjustsFontSizeToFitWidth = true

noResults.sizeToFit()


noResults.textColor = UIColor.lightGray
noResults.translatesAutoresizingMaskIntoConstraints = false

self.view.addSubview(noResults)

let yConstraint = NSLayoutConstraint(item: noResults, attribute: .centerY, relatedBy: .equal, toItem: noResults.superview, attribute: .centerY, multiplier: 1, constant: -(self.navigationController?.navigationBar.frame.height)!)
let xConstraint = NSLayoutConstraint(item: noResults, attribute: .centerX, relatedBy: .equal, toItem: noResults.superview, attribute: .centerX, multiplier: 1, constant: 0)


NSLayoutConstraint.activate([yConstraint, xConstraint])