ios - 如何以编程方式在 UIView 的中心添加文本？

Question

我有以下 UIView，如何以编程方式在该 UIView 的中心添加文本？​​

这是 UIView 代码:

    let newView = UIView()
    newView.backgroundColor = .groupTableViewBackground
    self.view.addSubview(newView)
    newView.translatesAutoresizingMaskIntoConstraints = false
    if #available(iOS 11.0, *) {
        let guide = self.view.safeAreaLayoutGuide
        newView.trailingAnchor.constraint(equalTo: guide.trailingAnchor).isActive = true
        newView.leadingAnchor.constraint(equalTo: guide.leadingAnchor).isActive = true
        newView.topAnchor.constraint(equalTo: guide.topAnchor).isActive = true
        newView.heightAnchor.constraint(equalToConstant: 50).isActive = true
    } else {
        NSLayoutConstraint(item: newView,
                           attribute: .top,
                           relatedBy: .equal,
                           toItem: view, attribute: .top,
                           multiplier: 1.0, constant: 0).isActive = true
        NSLayoutConstraint(item: newView,
                           attribute: .leading,
                           relatedBy: .equal, toItem: view,
                           attribute: .leading,
                           multiplier: 1.0,
                           constant: 0).isActive = true
        NSLayoutConstraint(item: newView, attribute: .trailing,
                           relatedBy: .equal,
                           toItem: view,
                           attribute: .trailing,
                           multiplier: 1.0,
                           constant: 0).isActive = true

        newView.heightAnchor.constraint(equalToConstant: 50).isActive = true
    }

这是我尝试以编程方式将文本添加到 UIView 的中心，但我不确定为什么它不起作用？

let lb = UILabel()
lb.centerXAnchor.constraint(equalTo: newView.centerXAnchor).isActive = true
lb.centerYAnchor.constraint(equalTo: newView.centerYAnchor).isActive = true
lb.text="anything"
newView.backgroundColor = UIColor.white

// show on screen
self.view.addSubview(newView)
newView.addSubview(lb)
lb.center = newView.center

更新:

如何在导航 Controller 下的 UIView 下方添加此按钮边框？

Answer 1

当涉及到以编程方式向 View 添加约束时，请注意，您必须将 translatesAutoresizingMaskIntoConstraints 设置为 false (但我感觉您已经知道这一点，并且只是忘了将其添加到标签中)

let lb = UILabel()
lb.textAlignment = .center
lb.numberOfLines = 0

newView.addSubview(lb)

lb.translatesAutoresizingMaskIntoConstraints = false
lb.centerXAnchor.constraint(equalTo: newView.centerXAnchor).isActive = true
lb.centerYAnchor.constraint(equalTo: newView.centerYAnchor).isActive = true

添加边框(假设您想将边框添加到newView):

let border = UIView()
newView.addSubview(border)

border.translatesAutoresizingMaskIntoConstraints = false

border.leadingAnchor.constraint(equalTo: newView.leadingAnchor).isActive = true
border.trailingAnchor.constraint(equalTo: newView.trailingAnchor).isActive = true
border.bottomAnchor.constraint(equalTo: newView.bottomAnchor).isActive = true
border.heightAnchor.constraint(equalToConstant: 1).isActive = true

但是对于边框，在 UIView 上编写扩展可能会更清晰，因此如果您再次需要它，代码可以在其他地方重用