UIViewのサイズを変更して、ラベルをその中に収めます

コードに .numberOfLines を設定したことが表示されない  ラベル内の 0  複数行のラベルを許可します。

それだけを追加すると、ラベルの高さが増し、カスタムビューが拡大できるようになります。ただし...これにより、両方のラベルが最も高いラベルのサイズに拡張され、「短い」ラベルのテキストが垂直方向の中央に配置されます（ビューのフレーム/境界を見やすくするために背景色を追加しました）：

カスタムビューの下部を greaterThanOrEqualTo の各ラベルの下部に制限する場合  ラベルを「上揃え」に保つことができます。

Playgroundページでこのコードを直接実行して、結果を確認できます。

//: A UIKit based Playground for presenting user interface
import UIKit
import PlaygroundSupport
class MyCustomView: UIView {
    public let leftLabel: UILabel = UILabel(frame: .zero)
    public let rightLabel: UILabel = UILabel(frame: .zero)
    override init(frame: CGRect) {
        super.init(frame: frame)
        addSubview(leftLabel)
        addSubview(rightLabel)
        // background colors so we can see the view frames
        backgroundColor = .cyan
        leftLabel.backgroundColor = .yellow
        rightLabel.backgroundColor = .green
        // we want multi-line labels
        leftLabel.numberOfLines = 0
        rightLabel.numberOfLines = 0
        // use auto-layout
        leftLabel.translatesAutoresizingMaskIntoConstraints = false
        rightLabel.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            // constrain to top
            leftLabel.topAnchor.constraint(equalTo: topAnchor),
            // constrain to left
            leftLabel.leadingAnchor.constraint(equalTo: leadingAnchor),
            // constrain width = 40%
            leftLabel.widthAnchor.constraint(equalTo: widthAnchor, multiplier: 0.4),
            // constrain to top
            rightLabel.topAnchor.constraint(equalTo: topAnchor),
            // constrain to right
            rightLabel.trailingAnchor.constraint(equalTo: trailingAnchor),
            // constrain width = 60%
            rightLabel.widthAnchor.constraint(equalTo: widthAnchor, multiplier: 0.6),
            // constrain bottom of view (self) to >= 0 from bottom of leftLabel
            bottomAnchor.constraint(greaterThanOrEqualTo: leftLabel.bottomAnchor, constant: 0.0),
            // constrain bottom of view (self) to >= 0 from bottom of rightLabel
            bottomAnchor.constraint(greaterThanOrEqualTo: rightLabel.bottomAnchor, constant: 0.0),
            ])
        leftLabel.text = "Short string"
        rightLabel.text = "Short string too"
    }
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}
class MyViewController : UIViewController {
    var theButton: UIButton = {
        let b = UIButton()
        b.setTitle("Tap Me", for: .normal)
        b.translatesAutoresizingMaskIntoConstraints = false
        b.backgroundColor = .red
        return b
    }()
    var theStackView: UIStackView = {
        let v = UIStackView()
        v.translatesAutoresizingMaskIntoConstraints = false
        v.axis = .vertical
        v.spacing = 8
        v.distribution = .equalSpacing
        return v
    }()
    var myView = MyCustomView()
    // on button tap, change the text in the label(s)
    @objc func didTap(_ sender: Any?) -> Void {
        myView.leftLabel.text = "Short string with\nA\nB\nC\nD\nE"
        myView.rightLabel.text = "Short string too\nA\nB"
    }
    override func loadView() {
        let view = UIView()
        self.view = view
        view.backgroundColor = .white
        view.addSubview(theButton)
        // constrain button to Top: 32 and centerX
        NSLayoutConstraint.activate([
            theButton.topAnchor.constraint(equalTo: view.topAnchor, constant: 32.0),
            theButton.centerXAnchor.constraint(equalTo: view.centerXAnchor, constant: 0.0),
            ])
        view.addSubview(theStackView)
        // constrain stack view to Top: 100 and Leading/Trailing" 0
        // no Bottom or Height constraint
        NSLayoutConstraint.activate([
            theStackView.topAnchor.constraint(equalTo: view.topAnchor, constant: 100.0),
            theStackView.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 0.0),
            theStackView.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: 0.0),
            ])
        theStackView.addArrangedSubview(myView)
        // add an action for the button tap
        theButton.addTarget(self, action: #selector(didTap(_:)), for: .touchUpInside)
    }
}
// Present the view controller in the Live View window
PlaygroundPage.current.liveView = MyViewController()