ios - UIStackView 无法满足的自动布局约束

Question

我在 Storyboard中定义了一个 UIStackView，第一个按钮的高度设置为 70，其他按钮的高度设置为 45。我收到此自动布局错误:

 [LayoutConstraints] Unable to simultaneously satisfy constraints.
Probably at least one of the constraints in the following list is one you don't want. 
Try this: 
    (1) look at each constraint and try to figure out which you don't expect; 
    (2) find the code that added the unwanted constraint or constraints and fix it. 
 (
"<NSLayoutConstraint:0x280f614f0 UIButton:0x10641a120.height == 45   (active)>",
"<NSLayoutConstraint:0x280f60e60 UIButton:0x106418f80.height == 70   (active)>",
"<NSLayoutConstraint:0x280f604b0 'UISV-alignment' UIButton:0x10641a120.bottom == UIButton:0x106418f80.bottom   (active)>",
"<NSLayoutConstraint:0x280f63cf0 'UISV-alignment' UIButton:0x10641a120.top == UIButton:0x106418f80.top   (active)>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x280f60e60 UIButton:0x106418f80.height == 70   (active)>

我知道 UIStackView 无法接受不同高度的 UIButton，这是否正确？让 UIStackView 接受其元素的不同高度或宽度的方法是什么？

Answer 1

堆栈 View 约束中的某些内容导致了问题。

这是一个有效的布局:

使用堆栈 View 属性:

通过代码添加第三个按钮之前的结果:

通过代码添加第三个按钮(高度限制为 60)后的结果:

没有自动布局警告或错误。

代码(连接到按钮 1)添加/删除 Button 3 作为堆栈 View 的排列 subview :

class TestViewController: UIViewController {

    @IBOutlet var theStackView: UIStackView!

    var thirdButton: UIButton = {
        let b = UIButton()
        b.translatesAutoresizingMaskIntoConstraints = false
        b.setTitle("Button 3", for: .normal)
        b.backgroundColor = .red
        return b
    }()

    @IBAction func doAddThird(_ sender: Any) {

        if theStackView.arrangedSubviews.count == 2 {

            theStackView.addArrangedSubview(thirdButton)

        } else {

            if let v = theStackView.arrangedSubviews.last {
                v.removeFromSuperview()
            }

        }

    }

    override func viewDidLoad() {
        super.viewDidLoad()

        // finish initializing the third button
        if let v = theStackView.arrangedSubviews.first as? UIButton {
            thirdButton.titleLabel?.font = v.titleLabel?.font
        }

        NSLayoutConstraint.activate([
            thirdButton.heightAnchor.constraint(equalToConstant: 60),
            ])

    }   
}