iOS 应用中的布局问题 (NSLayoutConstraint)

Question

在 iOS 应用程序中，我遇到了自动布局问题。

以下 2 个屏幕截图显示了问题。

右边的开关（UISwitch 对象）水平位移，应该固定。谁能看到发生了什么？

左边的字符串确实在改变长度，但我认为（根据我设置约束的方式）应该调整字体大小或将字符串分成两行；但开关没有移位。

这里是相关的swift代码：

import UIKit

class My_ViewController: UIViewController {
    let xPanel = UILabel(), yPanel = UILabel(),
    khToggle = UISwitch(), khLabel = UILabel()
    ....

    override func viewDidLoad() {
        super.viewDidLoad()
        layOutUI()
    }


    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        .....
        toggleKeepHide(khToggle)
    }


    func layOutUI() {
        for component in [xPanel,yPanel,khLabel,khToggle] {
            component.translatesAutoresizingMaskIntoConstraints = false
            view.addSubview(component)
        }

        ...........

        khLabel.numberOfLines = 0
        khLabel.adjustsFontSizeToFitWidth = true
        khToggle.addTarget(self,
                                 action: #selector(toggleKeepHide(_:)),
                                 for: .valueChanged)

        view.addConstraints([
            .........
            NSLayoutConstraint(item: khToggle, attribute: .right, relatedBy: .equal,
                               toItem: view, attribute: .right, multiplier: 1.0,    constant: -30.0),
            NSLayoutConstraint(item: khToggle, attribute: .top, relatedBy: .equal,
                               toItem: yPanel, attribute: .bottom, multiplier: 1.0,
                               constant: 50.0),
            NSLayoutConstraint(item: khLabel, attribute: .right, relatedBy: .equal,
                               toItem: khToggle, attribute: .left, multiplier: 1.0,     constant: -23.0),
            NSLayoutConstraint(item: khLabel, attribute: .centerY, relatedBy: .equal,
                               toItem: khToggle, attribute: .centerY, multiplier: 1.0,  constant: 0.0),
            NSLayoutConstraint(item: khLabel, attribute: .left, relatedBy: .equal,
                               toItem: view, attribute: .left, multiplier: 1.0,     constant: 30.0)])
    }


    @objc func toggleKeepHide(_ sender: UISwitch) {
        if sender.isOn {khLabel.text = "Hide this object from the wyxoug list."}
        else {khLabel.text = "Keep this object in the wyxoug list."}
    }
}

Answer 1

标签和切换的水平约束相互竞争。

（如果你进入Xcode的可视化调试器，你会发现有一个警告：UISwitch实例的宽度和水平位置不明确。）

解决方案

您为AutoLayout 提供了绝对值，它无法解析要求。要解决此问题，请通过将标签的抗压性设置为较低的值来为要求引入一些灵活性：

khLabel.setCompressionResistance(.defaultLow, for: .horizontal)

Answer 2

您没有提供足够的信息来重现问题。这是我的视图控制器 viewDidLoad 中代码的缩减（除了标签和开关，我删除了所有内容，修复了你的 left 和 right （你永远不应该使用它们），并改变了两个视图之间的对齐方式为 top 而不是 center):

    khToggle = UISwitch()
    khToggle.translatesAutoresizingMaskIntoConstraints = false
    self.view.addSubview(khToggle)

    khLabel = UILabel()
    khLabel.text = String(repeating: "word ", count: 40)
    khLabel.translatesAutoresizingMaskIntoConstraints = false
    self.view.addSubview(khLabel)


    // Do any additional setup after loading the view.
    khLabel.numberOfLines = 0

    view.addConstraints([
        NSLayoutConstraint(item: khToggle!, attribute: .trailing, relatedBy: .equal,
                               toItem: view, attribute: .trailing, multiplier: 1.0,    constant: -30.0),
        NSLayoutConstraint(item: khToggle!, attribute: .top, relatedBy: .equal,
                           toItem: view, attribute: .top, multiplier: 1.0,
                           constant: 50.0),
        NSLayoutConstraint(item: khLabel!, attribute: .trailing, relatedBy: .equal,
                           toItem: khToggle, attribute: .leading, multiplier: 1.0,     constant: -23.0),
        NSLayoutConstraint(item: khLabel!, attribute: .top, relatedBy: .equal,
                           toItem: khToggle, attribute: .top, multiplier: 1.0,  constant: 0.0),
        NSLayoutConstraint(item: khLabel!, attribute: .leading, relatedBy: .equal,
                           toItem: view, attribute: .leading, multiplier: 1.0,     constant: 30.0)])

结果显示正常；没有约束冲突或歧义，看起来就像人们期望的那样：

iOS 应用中的布局问题 (NSLayoutConstraint)

A layout issue (NSLayoutConstraint) in an iOS app

autolayout

nslayoutconstraint

swift