如何在堆栈视图中居中对齐视图，而不是拉伸任何视图或分布？

Question

我正在构建一个自定义的经度/纬度选择器。视图如下：

textfield ° textfield ′ textfield ″ N|S

组件都在堆栈视图中。我希望文本字段的宽度能够自动适应内容。这是我正在使用的代码（实际的布局代码并不多。大部分是样板）：

class DMSLongLatInputView : UIView {
    private var degreeTextField: DMSLongLatTextField!
    private var minuteTextField: DMSLongLatTextField!
    private var secondTextField: DMSLongLatTextField!
    var signSelector: UISegmentedControl!
    let fontSize: CGFloat = 22
    override init(frame: CGRect) {
        super.init(frame: frame)
        commonInit()
    }
    
    required init?(coder: NSCoder) {
        super.init(coder: coder)
        commonInit()
    }
    
    private func commonInit() {
        degreeTextField = DMSLongLatTextField()
        minuteTextField = DMSLongLatTextField()
        secondTextField = DMSLongLatTextField()
        signSelector = UISegmentedControl(items: ["N", "S"])
        signSelector.selectedSegmentIndex = 0
        signSelector.setTitleTextAttributes([.font: UIFont.systemFont(ofSize: fontSize)], for: .normal)
        [degreeTextField, minuteTextField, secondTextField].forEach { (tf) in
            tf?.font = UIFont.monospacedDigitSystemFont(ofSize: fontSize, weight: .regular)
        }
        let degreeLabel = UILabel()
        degreeLabel.text = "°"
        let minuteLabel = UILabel()
        minuteLabel.text = "′"
        let secondLabel = UILabel()
        secondLabel.text = "″"
        [degreeLabel, minuteLabel, secondLabel].forEach {
            l in l.font = UIFont.systemFont(ofSize: fontSize)
        }
        let stackView = UIStackView(arrangedSubviews:
            [degreeTextField,
             degreeLabel,
             minuteTextField,
             minuteLabel,
             secondTextField,
             secondLabel,
             signSelector
        ])
        stackView.arrangedSubviews.forEach { (v) in
            // I was hoping that this would make the widths of the stack view's subviews automatically
            // fit the content
            v.setContentCompressionResistancePriority(.required, for: .horizontal)
            v.setContentHuggingPriority(.required, for: .horizontal)
        }
        stackView.axis = .horizontal
        stackView.alignment = .center
        stackView.distribution = .fill
        addSubview(stackView)
        stackView.topAnchor.constraint(equalTo: self.topAnchor).isActive = true
        stackView.bottomAnchor.constraint(equalTo: self.bottomAnchor).isActive = true
        stackView.leadingAnchor.constraint(equalTo: self.leadingAnchor).isActive = true
        stackView.trailingAnchor.constraint(equalTo: self.trailingAnchor).isActive = true
        
        stackView.translatesAutoresizingMaskIntoConstraints = false
        backgroundColor = .clear
    }
}

fileprivate class DMSLongLatTextField: UITextField, UITextFieldDelegate {
    override init(frame: CGRect) {
        super.init(frame: frame)
        commonInit()
    }
    
    required init?(coder: NSCoder) {
        super.init(coder: coder)
        commonInit()
    }
    
    private func commonInit() {
        backgroundColor = .tertiarySystemFill
        placeholder = "00"
        borderStyle = .none
        textAlignment = .right
    }
}

这会产生：

即使我将内容拥抱优先级设置为.required，第一个文本字段也被拉长了很多。我希望第一个文本字段的宽度只有两位数，因为这就是它的占位符的宽度。

我怀疑这是因为我使用了错误的distribution，但我尝试了所有其他 4 个发行版，但都没有得到我想要的结果。例如，.equalSpacing 和 spacing = 0 给出了这个结果（从调试器中的 UI 层次结构检查器中可以看出）：

显然间距不是0！我希望所有子视图尽可能靠近，并保持中心对齐。我该怎么做？

Answer 1

您正在堆栈视图上设置前导和尾随...换句话说，您是在告诉自动布局：

“用子视图填充屏幕的宽度。”

将您的约束更改为：

    stackView.topAnchor.constraint(equalTo: self.topAnchor).isActive = true
    stackView.bottomAnchor.constraint(equalTo: self.bottomAnchor).isActive = true

    //stackView.leadingAnchor.constraint(equalTo: self.leadingAnchor).isActive = true
    //stackView.trailingAnchor.constraint(equalTo: self.trailingAnchor).isActive = true
    
    stackView.centerXAnchor.constraint(equalTo: self.centerXAnchor).isActive = true

这应该水平居中您的堆栈视图及其子视图。