在嵌套的UIStackView中添加多个排列的子视图时，它会中断布局，为什么？

Question

在使用UIStackView时遇到一个奇怪的问题，该问题不允许我在嵌套的UIStackView中添加额外安排的子视图：

 override func viewDidLoad() {
        super.viewDidLoad()

        view.backgroundColor = .white

        let subViews = [UIColor.gray, UIColor.darkGray, UIColor.lightGray].map { (color) -> UIView in
            let v = UIView()
            v.backgroundColor = color
            return v
        }

        let redView = UIStackView(arrangedSubviews: subViews)
        redView.distribution = .fillEqually
        redView.heightAnchor.constraint(lessThanOrEqualToConstant: 100).isActive = true


        let blueView = UIView()
        blueView.backgroundColor = .blue


        let buttons = [UIColor.gray, UIColor.darkGray, UIColor.lightGray].map { (color) -> UIView in
            let v = UIView()
            v.backgroundColor = color
            return v
        }

        let buttonsView = UIStackView(arrangedSubviews: buttons)
        buttonsView.distribution = .fillEqually
        buttonsView.heightAnchor.constraint(lessThanOrEqualToConstant: 100).isActive = true


        let stackView = UIStackView(arrangedSubviews: [redView, blueView, buttonsView])

        view.addSubview(stackView)
        stackView.axis = .vertical
        stackView.fillSuperview()

    }

结果是，我得到了完全拉伸的蓝色视图，而不是预期的行为：

但是当我在底部堆栈视图中保留一个子视图时，它会按预期显示

   let buttons = [UIColor.gray].map { (color) -> UIView in
        let v = UIView()
        v.backgroundColor = color
        return v
    }

    let buttonsView = UIStackView(arrangedSubviews: buttons)
    buttonsView.distribution = .fillEqually
    buttonsView.heightAnchor.constraint(lessThanOrEqualToConstant: 100).isActive = true


    let stackView = UIStackView(arrangedSubviews: [redView, blueView, buttonsView])

为什么？代码有什么问题？感谢您提供任何帮助或提示，我也尝试在顶部和底部堆栈视图上translatesAutoresizingMaskIntoConstraints = false，但没有任何运气

Answer 1

在底部stackview上需要设置 buttonView.heightAnchor.constraint(equalToConstant: 100).isActive = true

代替

buttonView.heightAnchor.constraint(lessThanOrEqualToConstant: 100).isActive = true