由于 NSLayoutConstraint 错误，具有 automaticDimension 的 UITableView 不会动态增加大小
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【中文标题】由于 NSLayoutConstraint 错误，具有 automaticDimension 的 UITableView 不会动态增加大小【英文标题】：UITableView with automaticDimension doesn't dynamically increase size due to NSLayoutConstraint error 【发布时间】：2019-03-25 06:07:48 【问题描述】：我正在创建一个自定义 UITableViewCell。目前，我只想让它在左侧有一个UIButton (checkButton)，在按钮的右侧有两个UILabels（titleLabel 和notesLabel）。
基本上，它应该看起来像一个标准的UITableViewCell，带有一个图像和两个文本标签（但请不要告诉我只是重复使用一个标准单元格，因为由于各种原因我不能这样做)。该按钮应具有固定大小 (16x16) 并在单元格中垂直居中。这两个标签应换行并展开以适合其内容。我正在尝试以编程方式定义此单元格，因此我创建了以下初始化程序来定义约束。
override init(style: UITableViewCell.CellStyle, reuseIdentifier: String?)
super.init(style: style, reuseIdentifier: reuseIdentifier)
titleLabel.translatesAutoresizingMaskIntoConstraints = false
titleLabel.font = UIFont.systemFont(ofSize: 16)
titleLabel.lineBreakMode = .byWordWrapping
titleLabel.numberOfLines = 0
contentView.addSubview(titleLabel)
checkButton.translatesAutoresizingMaskIntoConstraints = false
contentView.addSubview(checkButton)
notesLabel.translatesAutoresizingMaskIntoConstraints = false
notesLabel.font = UIFont.systemFont(ofSize: 13)
notesLabel.lineBreakMode = .byWordWrapping
notesLabel.numberOfLines = 0
contentView.addSubview(notesLabel)
addConstraint(NSLayoutConstraint(item: titleLabel,
attribute: .top,
relatedBy: .equal,
toItem: contentView,
attribute: .top,
multiplier: 1,
constant: 0))
addConstraint(NSLayoutConstraint(item: notesLabel,
attribute: .top,
relatedBy: .equal,
toItem: titleLabel,
attribute: .bottom,
multiplier: 1,
constant: 0))
addConstraint(NSLayoutConstraint(item: titleLabel,
attribute: .trailing,
relatedBy: .equal,
toItem: contentView,
attribute: .trailing,
multiplier: 1,
constant: -10))
addConstraint(NSLayoutConstraint(item: notesLabel,
attribute: .trailing,
relatedBy: .equal,
toItem: contentView,
attribute: .trailing,
multiplier: 1,
constant: -10))
addConstraint(NSLayoutConstraint(item: notesLabel,
attribute: .bottom,
relatedBy: .equal,
toItem: contentView,
attribute: .bottom,
multiplier: 1,
constant: 0))
addConstraint(NSLayoutConstraint(item: checkButton,
attribute: .leading,
relatedBy: .equal,
toItem: contentView,
attribute: .leading,
multiplier: 1,
constant: 20))
addConstraint(NSLayoutConstraint(item: checkButton,
attribute: .centerY,
relatedBy: .equal,
toItem: contentView,
attribute: .centerY,
multiplier: 1,
constant: 0))
addConstraint(NSLayoutConstraint(item: checkButton,
attribute: .height,
relatedBy: .equal,
toItem: nil,
attribute: .notAnAttribute,
multiplier: 0,
constant: 16))
addConstraint(NSLayoutConstraint(item: checkButton,
attribute: .width,
relatedBy: .equal,
toItem: nil,
attribute: .notAnAttribute,
multiplier: 0,
constant: 16))
addConstraint(NSLayoutConstraint(item: notesLabel,
attribute: .leading,
relatedBy: .equal,
toItem: checkButton,
attribute: .trailing,
multiplier: 1,
constant: 12))
addConstraint(NSLayoutConstraint(item: titleLabel,
attribute: .leading,
relatedBy: .equal,
toItem: checkButton,
attribute: .trailing,
multiplier: 1,
constant: 12))
当我运行这段代码时，它大部分都按预期工作，除了 Xcode 打印以下警告：[Warning] Warning once only: Detected a case where constraints ambiguously suggest a height of zero for a tableview cell's content view. We're considering the collapse unintentional and using standard height instead.
我通常会忽略这一点，但它似乎阻止了单元格扩展以适应其内容。例如，如果其中一个标签有足够的内容扩展到 3 行，则仅显示第一行。我想要的行为是让标签（以及扩展的单元格）扩展以适应它们的内容。我在高度限制方面做错了什么？
【问题讨论】：
约束应该添加到 contentView。 啊，谢谢！我现在可以停止拔头发了。如果您将其发布为答案，我会接受。 【参考方案1】：注意：请在单元格中添加标签和按钮，而不是在单元格的 contentView 中。下面的代码可以工作，如果有任何问题，请检查并告诉我。
override init(style: UITableViewCell.CellStyle, reuseIdentifier: String?)
super.init(style: style, reuseIdentifier: reuseIdentifier)
addSubview(titleLabel)
addSubview(checkButton)
addSubview(notesLabel)
titleLabel.translatesAutoresizingMaskIntoConstraints = false
titleLabel.font = UIFont.systemFont(ofSize: 16)
titleLabel.lineBreakMode = .byWordWrapping
titleLabel.numberOfLines = 0
checkButton.translatesAutoresizingMaskIntoConstraints = false
notesLabel.translatesAutoresizingMaskIntoConstraints = false
notesLabel.font = UIFont.systemFont(ofSize: 13)
notesLabel.lineBreakMode = .byWordWrapping
notesLabel.numberOfLines = 0
addConstraint(NSLayoutConstraint(item: titleLabel,
attribute: .top,
relatedBy: .equal,
toItem: self,
attribute: .top,
multiplier: 1,
constant: 0))
addConstraint(NSLayoutConstraint(item: notesLabel,
attribute: .top,
relatedBy: .equal,
toItem: titleLabel,
attribute: .bottom,
multiplier: 1,
constant: 0))
addConstraint(NSLayoutConstraint(item: titleLabel,
attribute: .trailing,
relatedBy: .equal,
toItem: self,
attribute: .trailing,
multiplier: 1,
constant: -10))
addConstraint(NSLayoutConstraint(item: notesLabel,
attribute: .trailing,
relatedBy: .equal,
toItem: self,
attribute: .trailing,
multiplier: 1,
constant: -10))
addConstraint(NSLayoutConstraint(item: notesLabel,
attribute: .bottom,
relatedBy: .equal,
toItem: self,
attribute: .bottom,
multiplier: 1,
constant: 0))
addConstraint(NSLayoutConstraint(item: checkButton,
attribute: .leading,
relatedBy: .equal,
toItem: self,
attribute: .leading,
multiplier: 1,
constant: 20))
addConstraint(NSLayoutConstraint(item: checkButton,
attribute: .centerY,
relatedBy: .equal,
toItem: self,
attribute: .centerY,
multiplier: 1,
constant: 0))
addConstraint(NSLayoutConstraint(item: checkButton,
attribute: .height,
relatedBy: .equal,
toItem: nil,
attribute: .notAnAttribute,
multiplier: 0,
constant: 16))
addConstraint(NSLayoutConstraint(item: checkButton,
attribute: .width,
relatedBy: .equal,
toItem: nil,
attribute: .notAnAttribute,
multiplier: 0,
constant: 16))
addConstraint(NSLayoutConstraint(item: notesLabel,
attribute: .leading,
relatedBy: .equal,
toItem: checkButton,
attribute: .trailing,
multiplier: 1,
constant: 12))
addConstraint(NSLayoutConstraint(item: titleLabel,
attribute: .leading,
relatedBy: .equal,
toItem: checkButton,
attribute: .trailing,
multiplier: 1,
constant: 12))
【讨论】：
感谢您的回答！看起来这样可行，但我更喜欢 Sachin 的方法，因为添加到内容视图中可以在模式之间转换时提供漂亮的动画等。【参考方案2】：这是我的方法
private func setUp()
self.selectionStyle = .none
self.contentView.backgroundColor = .white
let button = UIButton(frame: CGRect(x: 0, y: 0, width: 16, height: 16))
button.setImage(UIImage(named: "arrow"), for: .normal)
button.translatesAutoresizingMaskIntoConstraints = false
self.contentView.addSubview(button)
button.leadingAnchor.constraint(equalTo: self.contentView.leadingAnchor, constant: 8.0).isActive = true
button.centerYAnchor.constraint(equalTo: self.contentView.centerYAnchor).isActive = true
button.widthAnchor.constraint(equalToConstant: button.frame.width).isActive = true
button.heightAnchor.constraint(equalToConstant: button.frame.height).isActive = true
let view = UIView()
view.backgroundColor = .red
view.translatesAutoresizingMaskIntoConstraints = false
self.contentView.addSubview(view)
view.topAnchor.constraint(equalTo: self.contentView.topAnchor, constant: 8.0).isActive = true
view.leadingAnchor.constraint(equalTo: self.contentView.leadingAnchor, constant: button.frame.width + 16.0).isActive = true
view.trailingAnchor.constraint(equalTo: self.contentView.trailingAnchor, constant: 8.0).isActive = true
view.bottomAnchor.constraint(equalTo: self.contentView.bottomAnchor, constant: -8.0).isActive = true
titleLabel.translatesAutoresizingMaskIntoConstraints = false
titleLabel.numberOfLines = 0
view.addSubview(titleLabel)
titleLabel.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
titleLabel.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
titleLabel.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true
notesLabel.translatesAutoresizingMaskIntoConstraints = false
notesLabel.numberOfLines = 0
view.addSubview(notesLabel)
notesLabel.topAnchor.constraint(equalTo: titleLabel.bottomAnchor, constant: 8.0).isActive = true
notesLabel.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
notesLabel.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true
notesLabel.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
如果标签是多行动态高度，使用以下来启用自调整单元格
tableView.rowHeight = UITableView.automaticDimension
tableView.estimatedRowHeight = 44.0
func tableView(_ tableView: UITableView, heightForRowAt indexPath: IndexPath) -> CGFloat
return UITableView.automaticDimension
结果
【讨论】：
这很好，除了我会为估计的行高提供一个实际值。主要是滚动指示器不会在您滚动时闪烁和调整大小。此外，提供一个具体的值更有意义，说估计一个单元格的估计值并没有真正增加价值。以上是关于由于 NSLayoutConstraint 错误，具有 automaticDimension 的 UITableView 不会动态增加大小的主要内容，如果未能解决你的问题，请参考以下文章
调整 UITableViewCell 大小的 NSLayoutConstraint 错误
错误：NSInvalidUnarchiveOperationException：无法实例化名为 NSLayoutConstraint 的类