ios - 定位约束没有任何影响

Question

我正在尝试在 viewDidLoad 函数中对标签进行编码。标 checkout 现了，但我现在使用的代码不影响定位。我正在尝试对 viewDidLoad 函数中的所有内容进行编码。你可以看到下面的截图。

override func viewDidLoad() {
    super.viewDidLoad()

    let backbutton = UILabel()
    backbutton.backgroundColor = UIColor.orange
    backbutton.translatesAutoresizingMaskIntoConstraints = false
    backbutton.widthAnchor.constraint(equalToConstant: 300).isActive = true
    backbutton.heightAnchor.constraint(equalToConstant: 300).isActive = true
    backbutton.centerXAnchor.constraint(equalTo: backbutton.centerXAnchor, constant: 100).isActive = true
    backbutton.centerYAnchor.constraint(equalTo: backbutton.centerYAnchor, constant: 300).isActive = true
    view.addSubview(backbutton)
}

Answer 1

这就是如何将 label 对齐到 view 的 center 中，

let backbutton = UILabel()
view.addSubview(backbutton)

backbutton.backgroundColor = UIColor.orange
backbutton.translatesAutoresizingMaskIntoConstraints = false
backbutton.widthAnchor.constraint(equalToConstant: 300).isActive = true
backbutton.heightAnchor.constraint(equalToConstant: 300).isActive = true
backbutton.centerXAnchor.constraint(equalTo: view.centerXAnchor, constant: 0).isActive = true
backbutton.centerYAnchor.constraint(equalTo: view.centerYAnchor, constant: 0).isActive = true

当您以编程方式设置约束时，确保将view添加到super/parent view在应用 constraints 之前。其次，在下面几行中，您要告诉 backButton 标签将其中心与其自身对齐(即，backbutton.centerXAnchor.constraint(equalTo: backbutton.centerXAnchor)。

backbutton.centerXAnchor.constraint(equalTo: backbutton.centerXAnchor, constant: 100).isActive = true
backbutton.centerYAnchor.constraint(equalTo: backbutton.centerYAnchor, constant: 300).isActive = true

因为你想将其垂直和水平居中对齐到它的父 View 所以你应该设置center constraints 等于 parent view 如下，

backbutton.centerXAnchor.constraint(equalTo: view.centerXAnchor, constant: 0).isActive = true
backbutton.centerYAnchor.constraint(equalTo: view.centerYAnchor, constant: 0).isActive = true