ios – 以编程方式使用布局锚创建子视图

我已经使用布局锚点以编程方式创建了一个UIView.现在我想在这个视图中添加一个UILabel.到目前为止,这是我的代码：

let centerView = UIView()
centerView.translatesAutoresizingMaskIntoConstraints = false
centerView.backgroundColor = UIColor.white
view.addSubview(centerView)
centerView.leftAnchor.constraint(equalTo: view.leftAnchor,constraint: 20).isActive = true
centerView.rightAnchor.constraint(equalTo: view.rightAnchor,constraint: -20).isActive = true

let label = UILabel()
label.translatesAutoresizingMaskIntoConstraints = false
label.text = "Testing" 
label.textColor = UIColor.black
centerView.addSubview(label)
label.leftAnchor.constraint(equalTo: centerView.leftAnchor).isActive = true

我认为这个标签会在参考centerView时显示,但它是在参考UIWindow时显示的.这是当前的视图层次结构：

UIWindow --> UIView (centerView) --> UILabel (label)

我需要在centerView中添加多个标签,根据我的理解,这个链会变长,而我想要几个标签都在centerView下面

UIWindow

            |

     UIView (centerView)

     /      |      \
  Label 1  Label 2  Label 3

我怎样才能实现这种层次结构？

解决方法

你正确地做了,你没有提供足够的约束.我在Swift Playground中尝试了您的代码并添加了一些额外的约束,它显示标签相对于centerView按预期放置：

let view = UIView(frame: CGRect(x: 0,y: 0,width: 300,height: 500))

let centerView = UIView()
centerView.translatesAutoresizingMaskIntoConstraints = false
centerView.backgroundColor = UIColor.white
view.addSubview(centerView)
centerView.leftAnchor.constraint(equalTo: view.leftAnchor,constant: 20).isActive = true
centerView.rightAnchor.constraint(equalTo: view.rightAnchor,constant: -20).isActive = true
centerView.topAnchor.constraint(equalTo: view.topAnchor,constant: 20).isActive = true
centerView.bottomAnchor.constraint(equalTo: view.bottomAnchor,constant: -20).isActive = true

let label = UILabel()
label.translatesAutoresizingMaskIntoConstraints = false
label.text = "Testing"
label.textColor = UIColor.black
label.backgroundColor = UIColor.yellow
centerView.addSubview(label)
label.leftAnchor.constraint(equalTo: centerView.leftAnchor).isActive = true
label.topAnchor.constraint(equalTo: centerView.topAnchor).isActive = true

view.layoutIfNeeded()

这是在游乐场运行：