将尝试通过打破约束来恢复（但不确定为什么我的约束是错误的）

Question

我正在制作一个基于 this article 的自定义列表单元格（集合视图列表单元格）。我在单元格中手动添加视图的高度，但我在 Xcode 的控制台中看到下面的警告，并且不确定要修复哪个部分。

[LayoutConstraints] Unable to simultaneously satisfy constraints.
    Probably at least one of the constraints in the following list is one you don't want. 
translatesAutoresizingMaskIntoConstraints) 
    (
        "<NSAutoresizingMaskLayoutConstraint:0x281209220 h=--& v=--& liveTest.LiveChannelContentView:0x128c13430.height == 44   (active)>",
        "<NSLayoutConstraint:0x2812371b0 UIView:0x128c136b0.height == 60   (active)>",
        "<NSLayoutConstraint:0x2812372a0 V:|-(0)-[UIView:0x128c136b0]   (active, names: '|':liveTest.LiveChannelContentView:0x128c13430 )>",
        "<NSLayoutConstraint:0x2812372f0 UIView:0x128c136b0.bottom == liveTest.LiveChannelContentView:0x128c13430.bottom   (active)>"
    )
    
    Will attempt to recover by breaking constraint 
    <NSLayoutConstraint:0x2812371b0 UIView:0x128c136b0.height == 60   (active)>

下面的代码是我收到此错误消息的地方。

class LiveChannelContentView: UIView, UIContentView {
    
    let contentsView = UIView()
    
    lazy var titleLabel: UILabel = {
        let label = UILabel()
        label.text = ""
        return label
    }()
    
    lazy var statusLabel: UILabel = {
        let label = UILabel()
        label.text = ""
        return label
    }()
    
    lazy var symbolImageView: UIImageView = {
        let imageView = UIImageView()
        imageView.contentMode = .scaleAspectFit
        return imageView
    }()
    
    var liveEvent: LiveEvent?
    
    init(configuration: LiveChannelContentConfiguration) {
          // Custom initializer implementation here.
        super.init(frame: .zero)
        
        print("this is the view height: \(self.bounds.height)") // -> I get 0.0 in here
        setupAllViews()
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    func setupAllViews() {
        addSubview(contentsView)
        contentsView.addSubview(symbolImageView)
        contentsView.addSubview(indicator)
        contentsView.addSubview(titleLabel)
        contentsView.addSubview(statusLabel)

        contentsView.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            contentsView.leadingAnchor.constraint(equalTo: layoutMarginsGuide.leadingAnchor),
            contentsView.trailingAnchor.constraint(equalTo: layoutMarginsGuide.trailingAnchor),
            contentsView.topAnchor.constraint(equalTo: layoutMarginsGuide.topAnchor),
            contentsView.bottomAnchor.constraint(equalTo: layoutMarginsGuide.bottomAnchor),
            contentsView.heightAnchor.constraint(equalToConstant: 60)
        ])
        
        contentsView.backgroundColor = .yellow
        
        symbolImageView.centerY(leading: contentsView.leadingAnchor, trailing: nil, parent: contentsView, paddingLeft: 0, paddingRight: 0, size: CGSize(width: 50, height: 50))
        indicator.centerY(leading: contentsView.leadingAnchor, trailing: nil, parent: contentsView, paddingLeft: 0, paddingRight: 0, size: CGSize(width: 50, height: 50))
        
        titleLabel.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            titleLabel.leadingAnchor.constraint(equalTo: symbolImageView.trailingAnchor, constant: 8),
            titleLabel.topAnchor.constraint(equalTo: symbolImageView.topAnchor),
            titleLabel.trailingAnchor.constraint(equalTo: contentsView.trailingAnchor)
        ])
        
        statusLabel.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
            statusLabel.leadingAnchor.constraint(equalTo: titleLabel.leadingAnchor),
            statusLabel.topAnchor.constraint(equalTo: titleLabel.bottomAnchor),
            statusLabel.trailingAnchor.constraint(equalTo: titleLabel.trailingAnchor)
        ])
        
        print("this is the view after setup: \(self.bounds.height)") // I also get 0.0 in here
    }
}

因此，为了阐明 LiveChannelContentView 的位置，我只是将黄色背景添加到视图中。有两件事我不明白。首先，甚至 Xcode 告诉我

    Will attempt to recover by breaking constraint

    <NSLayoutConstraint:0x2812371b0 UIView:0x128c136b0.height == 60   (active)>

当我截取应用程序的屏幕截图并测量黄色背景 UIView 的高度时，它仍然是 60。我认为打破约束意味着使用其他高度约束而不是 60，但这是错误的吗？

另一件事是我很好奇

"<NSAutoresizingMaskLayoutConstraint:0x281209220 h=--& v=--& liveTest.LiveChannelContentView:0x128c13430.height == 44 (active)>" is used in my code. I searched the file contains 44 in my workspace but I got nothing.

不太确定，但我认为 44 和 60 的高度应用于相同的 UIView 并且 Xcode 摆脱了 60 的高度锚点或其他东西。但是，当我删除 contentsView 的高度锚点时，contentsView.heightAnchor.constraint(equalToConstant: 60)，应用程序崩溃如下。

我也试过删除 contentsView 的顶部或底部锚点，但它也破坏了应用程序。

contentsView.topAnchor.constraint(equalTo: layoutMarginsGuide.topAnchor),

或

contentsView.bottomAnchor.constraint(equalTo: layoutMarginsGuide.bottomAnchor),

所以谁能告诉我我应该修复哪个约束以消除警告？

Answer 1

更改此部分

    contentsView.translatesAutoresizingMaskIntoConstraints = false
    NSLayoutConstraint.activate([
        contentsView.leadingAnchor.constraint(equalTo: layoutMarginsGuide.leadingAnchor),
        contentsView.trailingAnchor.constraint(equalTo: layoutMarginsGuide.trailingAnchor),
        contentsView.topAnchor.constraint(equalTo: layoutMarginsGuide.topAnchor),
        contentsView.bottomAnchor.constraint(equalTo: layoutMarginsGuide.bottomAnchor),
        contentsView.heightAnchor.constraint(equalToConstant: 60)
    ])

至

contentsView.translatesAutoresizingMaskIntoConstraints = false

let con = contentsView.bottomAnchor.constraint(equalTo: layoutMarginsGuide.bottomAnchor)
con.priority = UILayoutPriority(rawValue: 999)  
    NSLayoutConstraint.activate([
        contentsView.leadingAnchor.constraint(equalTo: layoutMarginsGuide.leadingAnchor),
        contentsView.trailingAnchor.constraint(equalTo: layoutMarginsGuide.trailingAnchor),
        contentsView.topAnchor.constraint(equalTo: layoutMarginsGuide.topAnchor),
        con,
        contentsView.heightAnchor.constraint(equalToConstant: 60)
    ])

将尝试通过打破约束来恢复（但不确定为什么我的约束是错误的）

Will attempt to recover by breaking constraint (but not sure why my constraints are wrong)

ios

swift

autolayout

constraints