UITableView在更改出现排队后影响单元格高度的约束时发生UITableView,最终以破坏的约束结束

问题描述:

此代码块试图解决问题的核心问题。如果在将一个单元格出队后(通过configure)更改了约束条件,以便更改单元格高度,那么最终会出现损坏的约束警告(Unable to simultaneously satisfy constraints ...)。但是,它显示正确。UITableView在更改出现排队后影响单元格高度的约束时发生UITableView,最终以破坏的约束结束

import UIKit 
class ViewController: UIViewController { 

    @IBOutlet var tableView: UITableView! 

    override func viewDidLoad() { 
     super.viewDidLoad() 
     tableView.delegate = self 
     tableView.dataSource = self 
     tableView.registerClass(Cell.self, forCellReuseIdentifier: "cell") 
     tableView.estimatedRowHeight = 55.0 
     tableView.rowHeight = UITableViewAutomaticDimension 
    } 

} 

extension ViewController: UITableViewDelegate, UITableViewDataSource { 
    func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int { 
     return array.count 
    } 

    func numberOfSectionsInTableView(tableView: UITableView) -> Int { 
     return 1 
    } 

    func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell { 
     let cell = tableView.dequeueReusableCellWithIdentifier("cell") as! Cell 
     cell.configure(array[indexPath.row]) 
     return cell 
    } 

    func tableView(tableView: UITableView, willDisplayCell cell: UITableViewCell, forRowAtIndexPath indexPath: NSIndexPath) { 
    } 
} 

enum Position { 
    case Top 
    case Middle 
    case Bottom 
} 

class Cell: UITableViewCell { 

    private var topConstraint: NSLayoutConstraint! 
    private var bottomConstraint: NSLayoutConstraint! 

    private let label = UILabel() 
    private var previous: Position? 

    override init(style: UITableViewCellStyle, reuseIdentifier: String?) { 
     super.init(style: style, reuseIdentifier: reuseIdentifier) 

     label.backgroundColor = UIColor.redColor().colorWithAlphaComponent(0.5) 
     label.textColor = UIColor.blackColor() 
     label.translatesAutoresizingMaskIntoConstraints = false 
     contentView.addSubview(label) 
     label.leadingAnchor.constraintEqualToAnchor(contentView.leadingAnchor, constant: 30).active = true 
     label.trailingAnchor.constraintEqualToAnchor(contentView.trailingAnchor, constant: -30).active = true 
     topConstraint = label.topAnchor.constraintEqualToAnchor(contentView.topAnchor) 
     topConstraint.active = true 
     bottomConstraint = label.bottomAnchor.constraintEqualToAnchor(contentView.bottomAnchor) 
     bottomConstraint.active = true 
    } 

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

    func configure(position: Position) { 
     if previous != nil {print("previous \(previous!) new \(position)")} 
     topConstraint.constant = position == .Top ? 30 : 0 
     bottomConstraint.constant = position == .Bottom ? -30 : 0 
     label.text = String(position) 
     previous = position 
    } 
} 

let array: [Position] = [.Top, .Middle, .Middle, .Middle, .Bottom, 
         .Top, .Middle, .Middle, .Middle, .Middle, .Bottom, 
         .Top, .Middle, .Middle, .Bottom, 
         .Top, .Middle, .Middle, .Middle, .Middle, .Middle, .Middle, .Bottom, 
         .Top, .Middle, .Middle, .Middle, .Bottom, 
         .Top, .Bottom, 
         .Top, .Middle, .Middle, .Middle, .Middle, .Middle, .Middle, .Bottom, 
         .Top, .Middle, .Middle, .Middle, .Bottom, 
         .Top, .Middle, .Middle, .Bottom, 
         .Top, .Middle, .Middle, .Middle, .Middle, .Middle, .Middle, .Bottom, 
] 

错误消息是...

2016-04-28 22:56:29.831 test-constraint-change[51059:3776208] 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:0x7c117c70 V:|-(30)-[UILabel:0x7c148770'Middle'] (Names: '|':UITableViewCellContentView:0x7c149b70)>", 
"<NSLayoutConstraint:0x7c115bd0 UILabel:0x7c148770'Middle'.bottom == UITableViewCellContentView:0x7c149b70.bottom>", 
"<NSLayoutConstraint:0x7c14a3f0 'UIView-Encapsulated-Layout-Height' V:[UITableViewCellContentView:0x7c149b70(20.5)]>" 
) 

Will attempt to recover by breaking constraint <NSLayoutConstraint:0x7c115bd0 UILabel:0x7c148770'Middle'.bottom == UITableViewCellContentView:0x7c149b70.bottom> 

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. 
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你得到的错误是什么?请向我们展示确切的堆栈跟踪和错误消息。 – ozgur

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完成,但3个约束没有任何技术上的错误。当时,他们应该强制细胞高度变大(细胞高度是动态的)。该单元正在从“中”向“顶”类型发展。 –

设置你的约束优先级999就像现在,它会正确显示。

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感谢您的回复......我确信这会做到这一点。但感觉有点哈克。希望找到一个干净的方式来做到这一点。 (我也可以忽略这些警告) –

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这是您最干净的解决方案,并且与自动布局的工作方式有关。使用自动调整表格单元格,系统隐式添加高度约束('UIView-Encapsulated-Layout-Height')。设置优先级允许自动布局优雅地解决这些冲突。请参阅:https://www.raywenderlich.com/87975/dynamic-table-view-cell-height-ios-8-swift –

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好的,我认为这只与动态高度有关。我们也注意到与宽度完全相同的问题(不同的场景)。尽可能多的解决方案,仍然感觉像一个自动布局的错误。你怎么看? –