ios - Stackview inside 其他 stackview 宽度问题

Question

我在 IB 中创建了一个 Stackview，它具有垂直方向。此堆栈 View 与父 View 的宽度相等。

例如，现在我以编程方式创建了一个 Stackview

let stackViewHorizontal   = UIStackView()
    stackViewHorizontal.axis  = UILayoutConstraintAxis.horizontal
    stackViewHorizontal.distribution  = UIStackViewDistribution.fillEqually
    stackViewHorizontal.alignment = UIStackViewAlignment.leading
    stackViewHorizontal.spacing = 8
    stackViewHorizontal.translatesAutoresizingMaskIntoConstraints = false
    stackViewHorizontal.leadingAnchor.constraint(equalTo: mainStackView.leadingAnchor,constant:0)
    stackViewHorizontal.trailingAnchor.constraint(equalTo: mainStackView.trailingAnchor,constant:0)

这里的 mainStackView 是一个通过 IB 创建的堆栈 View 。stackviewHorizo​​ntal 是一个以编程方式创建的堆栈 View 。我将 UILabels 放入 stackViewHorizo​​ntal 中。我预计这将扩展到全长，并且每个 UiLabel 将占据屏幕宽度的 50%，因为 stackview 具有水平轴并且分布是 fillEqually。

但我有一个 UiLabel 水平相邻。但不占用整个屏幕宽度

请告知我做错了什么？

Answer 1

激活约束，同时给它一个高度:

    stackViewHorizontal.leadingAnchor.constraint(equalTo: mainStackView.leadingAnchor,constant:0).isActive = true
    stackViewHorizontal.trailingAnchor.constraint(equalTo: mainStackView.trailingAnchor,constant:0).isActive = true

或

    NSLayoutConstraint.activate([
       stackViewHorizontal.leadingAnchor.constraint(equalTo: mainStackView.leadingAnchor,constant:0), 
       stackViewHorizontal.trailingAnchor.constraint(equalTo: mainStackView.trailingAnchor,constant:0) 
    ])

//

    let stackViewHorizontal   = UIStackView()
    stackViewHorizontal.axis  = UILayoutConstraintAxis.horizontal
    stackViewHorizontal.distribution  = UIStackViewDistribution.fillEqually
    stackViewHorizontal.alignment = UIStackViewAlignment.leading
    stackViewHorizontal.spacing = 8
    self.view.addSubview(stackViewHorizontal) //// add it here 
    stackViewHorizontal.translatesAutoresizingMaskIntoConstraints = false
    stackViewHorizontal.leadingAnchor.constraint(equalTo: mainStackView.leadingAnchor, constant: 0).isActive = true
    stackViewHorizontal.trailingAnchor.constraint(equalTo: mainStackView.trailingAnchor, constant: 0).isActive = true