UITableViewCell - 无法同时满足约束

Posted 2023-03-15

【中文标题】UITableViewCell - 无法同时满足约束

【英文标题】：UITableViewCell - unable to simultaneously satisfy constraints

【发布时间】：2018-07-14 17:36:11

【问题描述】：

我正在使用 SnapKit 来进行约束并以编程方式创建视图。但是，有一点我无法理解。

我想在表格视图单元格的内容视图中添加一个子 UIView 并设置它的高度。这已经导致不可满足的约束错误。

我也尝试在表格视图中设置（估计的）rowHeight，但这没有帮助。

2018-07-14 19:21:38.785556+0200[20027:748731] [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. 
(
    "<SnapKit.LayoutConstraint:[e-mail]#24 UIView:0x7fa342409240.top == UITableViewCellContentView:0x7fa342413970.top>",
    "<SnapKit.LayoutConstraint:[e-mail]#24 UIView:0x7fa342409240.bottom == UITableViewCellContentView:0x7fa342413970.bottom>",
    "<SnapKit.LayoutConstraint:[e-mail]#26 UIView:0x7fa342409240.height == 145.784842967987>",
    "<NSLayoutConstraint:0x604000282210 'UIView-Encapsulated-Layout-Height' UITableViewCellContentView:0x7fa342413970.height == 146   (active)>"
)

Will attempt to recover by breaking constraint 
<SnapKit.LayoutConstraint:[e-mail]#26 UIView:0x7fa342409240.height == 145.784842967987>

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

单元格代码：

class WeatherCell: UITableViewCell 
    override init(style: UITableViewCellStyle, reuseIdentifier: String?) 
        super.init(style: style, reuseIdentifier: reuseIdentifier)

        let expandView = UIView()

        self.contentView.addSubview(expandView)

        expandView.snp.makeConstraints  view in
            view.edges.equalToSuperview()

            view.height.equalTo(CGFloat(Float(arc4random()) / Float(UINT32_MAX)) * 200)
        
    

    required init?(coder aDecoder: NSCoder) 
        fatalError("init(coder:) has not been implemented")
    

【参考方案1】：

您需要引用底部约束并将其优先级更改为 999 / high 但不是 required ，因此删除边缘约束并分别制作它们

let expandView = UIView()
self.contentView.addSubview(expandView)
expandView.snp.makeConstraints  (view) in
    view.bottom.equalTo(self.contentView).priority(999) // can also be .priority(.high)
    view.top.left.right.equalTo(self.contentView)
    view.height.equalTo(CGFloat(Float(arc4random()) / Float(UINT32_MAX)) * 200)

【讨论】：

在自动布局根据内容计算正确高度之前，它在日志UIView-Encapsulated-Layout Height UITableViewCellContentView:0x7fa342413970.height == 146中假设一个静态高度，这肯定与当前内容高度冲突，因此这个日志，布局过程是递归，当您将底部约束的优先级设置为 none-required 时，此约束将被省略，直到自动布局最终确定并使其满足而不中断

@Sh_Khan 我遇到了类似的问题。如果我将底部约束的优先级降低到 999，我将不再收到冲突约束消息，但有时会在单元格之间出现死区。有什么想法吗？