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我试图用Swift 3以编程方式构建窗体，并且出于某种原因在运行应用程序时没有应用正确的约束。iOS Swift 3/XCode 8右约束没有应用
我有什么是UIScollView含有UITextField，你可以从下面的滚动型预览看到的是红色和文本字段是白色的。
// View Controller Properties
var scrollView: UIScrollView!
var firstName: UITextField!
// Inside viewDidLoad()
self.scrollView = UIScrollView()
self.scrollView.translatesAutoresizingMaskIntoConstraints = false
self.scrollView.backgroundColor = UIColor.red
self.scrollView.contentInset = UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 0)
self.view.addSubview(self.scrollView)
let top = NSLayoutConstraint(item: self.scrollView, attribute: .top, relatedBy: .equal, toItem: self.view, attribute: .top, multiplier: 1, constant: 0)
let left = NSLayoutConstraint(item: self.scrollView, attribute: .left, relatedBy: .equal, toItem: self.view, attribute: .left, multiplier: 1, constant: 0)
let right = NSLayoutConstraint(item: self.scrollView, attribute: .right, relatedBy: .equal, toItem: self.view, attribute: .right, multiplier: 1, constant: 0)
let bottom = NSLayoutConstraint(item: self.scrollView, attribute: .bottom, relatedBy: .equal, toItem: self.view, attribute: .bottom, multiplier: 1, constant: 0)
self.view.addConstraints([top, left, right, bottom])
self.firstName = UITextField()
self.firstName.translatesAutoresizingMaskIntoConstraints = false
self.firstName.backgroundColor = UIColor.white
self.firstName.placeholder = "First Name"
self.scrollView.addSubview(self.firstName)
let top = NSLayoutConstraint(item: self.firstName, attribute: .top, relatedBy: .equal, toItem: self.scrollView, attribute: .top, multiplier: 1, constant: 20)
let left = NSLayoutConstraint(item: self.firstName, attribute: .left, relatedBy: .equal, toItem: self.scrollView, attribute: .left, multiplier: 1, constant: 20)
let right = NSLayoutConstraint(item: self.firstName, attribute: .right, relatedBy: .equal, toItem: self.scrollView, attribute: .right, multiplier: 1, constant: 0)
let height = NSLayoutConstraint(item: self.firstName, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 40)
self.scrollView.addConstraints([top, right, left, height])
我尝试使用.trailing和.trailingMargin代替，但没有什么工作。任何建议将不胜感激。
