UITableViewCell 编程约束问题

Question

我正在使用编程约束创建 UITableViewCell。该呼叫有一个

cardView

和

button

。单独使用cardView就可以正常工作。但是一旦我添加

UIButton

到那里，我就可以在控制台上看到错误。

完整代码：

import UIKit

class ViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {

    private lazy var tableView: UITableView = {
    
        let view = UITableView()
        
        self.view.addSubview(view)
        view.translatesAutoresizingMaskIntoConstraints = false
        view.leftAnchor.constraint(equalTo: self.view.leftAnchor).isActive = true
        view.rightAnchor.constraint(equalTo: self.view.rightAnchor).isActive = true
        view.topAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.topAnchor).isActive = true
        view.bottomAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.bottomAnchor).isActive = true
        return view
        
    }()
    
    override func viewDidLoad() {
        super.viewDidLoad()
    
        tableView.register(Cell.self, forCellReuseIdentifier: "Cell")
        tableView.separatorStyle = .none
        
        tableView.delegate = self
        tableView.dataSource = self
    }
 
     
    func numberOfSections(in tableView: UITableView) -> Int {
        
        return 1
    }
    
    func tableView(_ tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
          
        return 1
    }
    
    func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
         
        let cell: Cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath) as! Cell
        cell.configure()
        return cell
    }
    
    func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        
        print("selected: \(indexPath.row)")
    }
}
 
private final class Cell: UITableViewCell {
    
    override init(style: UITableViewCell.CellStyle, reuseIdentifier: String?) {
        super.init(style: style, reuseIdentifier: reuseIdentifier)
        
        self.backgroundColor  = .clear
        self.selectionStyle = .none
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    private lazy var cardView: UIView = {
       
        let view = UIView()
        self.contentView.addSubview(view)
        view.translatesAutoresizingMaskIntoConstraints = false
 
        NSLayoutConstraint.activate([
            
            view.leftAnchor.constraint(equalTo: self.contentView.leftAnchor, constant: 18),
            view.topAnchor.constraint(equalTo: self.contentView.topAnchor, constant: 9),
            view.rightAnchor.constraint(equalTo: self.contentView.rightAnchor, constant: -18),
            view.bottomAnchor.constraint(equalTo: self.contentView.bottomAnchor, constant: -9),
            view.heightAnchor.constraint(equalToConstant: 60)
        ])
        
        view.layer.cornerRadius = 8
        view.layer.borderColor = UIColor.lightGray.withAlphaComponent(0.7).cgColor
        view.layer.borderWidth = 1.0
        return view
    }()
 
    private(set) lazy var buttonOptions: UIButton = {
       
        let button = UIButton()
        self.cardView.addSubview(button)
        button.translatesAutoresizingMaskIntoConstraints = false
        NSLayoutConstraint.activate([
         
            button.widthAnchor.constraint(equalToConstant: 22),
            button.heightAnchor.constraint(equalToConstant: 18),
            button.centerXAnchor.constraint(equalTo: self.cardView.centerXAnchor),
            button.centerYAnchor.constraint(equalTo: self.cardView.centerYAnchor)
        ])
        
        button.backgroundColor = UIColor.lightGray.withAlphaComponent(0.6)
        button.setImage(UIImage(systemName: "ellipsis")!, for: .normal)
        button.imageView?.tintColor = UIColor.lightGray
        return button
    }()
     
     
    func configure() {
         
        self.cardView.backgroundColor = .white
        self.buttonOptions.isHidden = false
    }
}

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:0x6000005b7480 V:|-(9)-[UIView:0x7ff5ac9066e0]   (active, names: '|':UITableViewCellContentView:0x7ff5ac90d4d0 )>",
    "<NSLayoutConstraint:0x6000005b7520 UIView:0x7ff5ac9066e0.bottom == UITableViewCellContentView:0x7ff5ac90d4d0.bottom - 9   (active)>",
    "<NSLayoutConstraint:0x6000005b7570 UIView:0x7ff5ac9066e0.height == 60   (active)>",
    "<NSLayoutConstraint:0x60000059c3c0 'UIView-Encapsulated-Layout-Height' UITableViewCellContentView:0x7ff5ac90d4d0.height == 44   (active)>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x6000005b7570 UIView:0x7ff5ac9066e0.height == 60   (active)>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKitCore/UIView.h> may also be helpful.

在单元格配置中，如果我评论

self.buttonOptions.isHidden = false

，那么我看不到任何警告。我不确定我在这里缺少什么，请帮我解决这个问题。

Answer 1

乍一看，默认的表格视图高度（44）和自定义视图高度（60）之间存在冲突。

然后我在

UIViewAlertForUnsatisfiableConstraints

处放置一个断点。太奇怪了，它在

button.imageView

上。在我看来，它有正确的限制。注释掉这一行，它就像一个魅力。

//button.imageView?.tintColor = UIColor.lightGray

结论：我认为这是一个系统错误，理论上，系统高度（44）优先，其优先级为1000。因此，解决方法是降低

cardView

的优先级。然后警告就消失了。即：

var height = view.heightAnchor.constraint(equalToConstant: 60)
height.priority = .init(999)
height.isActive = true