用不同的字体大小对齐UIButton和UILabel文本。

Question

我有一个 UIButton 和a UILabel 显示在行内。它们有不同大小的字体，但我想把它们对齐，使它们显示在同一行。

目前 UILabel 是略高于基线的 UIButton.

我希望避免手动设置内容偏移，因为我希望尽可能地正确缩放。我担心手动计算可能会对改变字体大小等产生意想不到的副作用。

我已经创建了一个游乐场，应该显示这2个元素。

//: A UIKit based Playground for presenting user interface

import UIKit
import PlaygroundSupport

class MyViewController : UIViewController {

  lazy var nameButton = configure(UIButton(type: .system), using: {
    $0.translatesAutoresizingMaskIntoConstraints = false
    $0.titleLabel?.font = .systemFont(ofSize: 18)
    $0.setTitleColor(.darkGray, for: .normal)
    $0.contentHorizontalAlignment = .leading
    $0.setContentHuggingPriority(UILayoutPriority.defaultHigh, for: .horizontal)
    $0.backgroundColor = .lightGray
    $0.setTitle("This is a button", for: .normal)
  })

  lazy var publishedDateLabel = configure(UILabel(frame: .zero), using: {
    $0.translatesAutoresizingMaskIntoConstraints = false
    $0.font = .systemFont(ofSize: 14)
    $0.textColor = .darkGray
    $0.setContentHuggingPriority(UILayoutPriority.defaultLow, for: .horizontal)
    $0.backgroundColor = .lightGray
    $0.text = "and this is a label"
  })

  override func loadView() {
    let view = UIView()
    view.backgroundColor = .white

    [nameButton, publishedDateLabel].forEach(view.addSubview(_:))

    NSLayoutConstraint.activate([
      nameButton.centerYAnchor.constraint(equalTo: view.centerYAnchor),
      nameButton.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 8),

      publishedDateLabel.centerYAnchor.constraint(equalTo: view.centerYAnchor),
      publishedDateLabel.leadingAnchor.constraint(equalTo: nameButton.trailingAnchor),
      publishedDateLabel.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -8)
    ])

    self.view = view
  }

  // setup helper method
  func configure<T>(_ value: T, using closure: (inout T) throws -> Void) rethrows -> T {
    var value = value
    try closure(&value)
    return value
  }
}
// Present the view controller in the Live View window
PlaygroundPage.current.liveView = MyViewController()

我试着让标签和按钮具有相同的高度，通过添加 publishedDateLabel.heightAnchor.constraint(equalTo: nameButton.heightAnchor)

然而这并没有改变对齐方式。

我还尝试使用 publishedDateLabel.lastBaselineAnchor.constraint(equalTo: nameButton.lastBaselineAnchor) 来对准锚点，但是这样就对准了元素的顶部。

如何将按钮中的文字底部与标签中的文字底部对齐？

Answer 1

只需注释出 heightAnchor 使用 lastBaselineAnchor:

NSLayoutConstraint.activate([
      nameButton.centerYAnchor.constraint(equalTo: view.centerYAnchor),
      nameButton.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 8),

      publishedDateLabel.lastBaselineAnchor.constraint(equalTo: nameButton.lastBaselineAnchor),
      publishedDateLabel.leadingAnchor.constraint(equalTo: nameButton.trailingAnchor),
      publishedDateLabel.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -8)
    ])