如何创建UILabel动态高度和布局锚点约束？

Question

我有一个UILabel，它使用不同长度的文本进行更新，并使用布局锚点约束定位。我无法获得正确的身高。有时最后一行被切断，但并非总是如此。

定义标签

message.textAlignment = .center
message.numberOfLines = 0
message.preferredMaxLayoutWidth = frame.width
message.lineBreakMode = .byWordWrapping
popUpWindow.addSubview(message)

message.translatesAutoresizingMaskIntoConstraints = false
message.topAnchor.constraint(equalTo: imageView.bottomAnchor, constant: POP_UP.SPACING_Y).isActive = true
message.leftAnchor.constraint(equalTo: layoutGuide.leftAnchor, constant: POP_UP.EDGE_INSET).isActive = true
message.rightAnchor.constraint(equalTo: layoutGuide.rightAnchor, constant: -POP_UP.EDGE_INSET).isActive = true
message.bottomAnchor.constraint(equalTo: cancel.topAnchor, constant: -POP_UP.SPACING_Y).isActive = true```

更新文本。 newText的长度有所不同。

message.text = newText
message.sizeToFit()
setNeedsLayout()

样本输入：

newText = "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua."

请注意“ ut Labore et dolore magna aliqua”。被切断。

（完整的布局约束供参考）

let layoutGuide = popUpWindow.safeAreaLayoutGuide

popUpWindow.translatesAutoresizingMaskIntoConstraints = false
popUpWindow.centerXAnchor.constraint(equalTo: safeAreaLayoutGuide.centerXAnchor).isActive = true
popUpWindow.centerYAnchor.constraint(equalTo: safeAreaLayoutGuide.centerYAnchor).isActive = true
popUpWindow.widthAnchor.constraint(equalTo: safeAreaLayoutGuide.widthAnchor, multiplier: 0.75).isActive = true

imageView.translatesAutoresizingMaskIntoConstraints = false
imageView.topAnchor.constraint(equalTo: layoutGuide.topAnchor, constant: POP_UP.EDGE_INSET).isActive = true
imageView.centerXAnchor.constraint(equalTo: popUpWindow.centerXAnchor).isActive = true
imageView.widthAnchor.constraint(equalTo: popUpWindow.widthAnchor, multiplier: 0.35).isActive = true

message.translatesAutoresizingMaskIntoConstraints = false
message.topAnchor.constraint(equalTo: imageView.bottomAnchor, constant: POP_UP.SPACING_Y).isActive = true
message.leftAnchor.constraint(equalTo: layoutGuide.leftAnchor, constant: POP_UP.EDGE_INSET).isActive = true
message.rightAnchor.constraint(equalTo: layoutGuide.rightAnchor, constant: -POP_UP.EDGE_INSET).isActive = true
message.bottomAnchor.constraint(equalTo: cancel.topAnchor, constant: -POP_UP.SPACING_Y).isActive = true

cancel.translatesAutoresizingMaskIntoConstraints = false
cancel.topAnchor.constraint(equalTo: message.bottomAnchor, constant: POP_UP.SPACING_Y).isActive = true
cancel.leftAnchor.constraint(equalTo: layoutGuide.leftAnchor, constant: POP_UP.EDGE_INSET).isActive = true
cancel.bottomAnchor.constraint(equalTo: layoutGuide.bottomAnchor, constant: -POP_UP.EDGE_INSET).isActive = true

ok.translatesAutoresizingMaskIntoConstraints = false
ok.topAnchor.constraint(equalTo: message.bottomAnchor, constant: POP_UP.SPACING_Y).isActive = true
ok.rightAnchor.constraint(equalTo: layoutGuide.rightAnchor, constant: -POP_UP.EDGE_INSET).isActive = true
ok.leftAnchor.constraint(equalTo: cancel.rightAnchor, constant: POP_UP.SPACING_X).isActive = true
ok.heightAnchor.constraint(equalTo: cancel.heightAnchor).isActive = true
ok.widthAnchor.constraint(equalTo: cancel.widthAnchor).isActive = true

更新： 我注意到我的首选宽度与左右约束锚之间存在不匹配，这可能导致计算出的高度比应该的短。

如果有人遇到相同问题，这是我所做的更新：

更改了首选宽度：

message.preferredMaxLayoutWidth = frame.width * 0.5

删除了左右锚点约束，并添加了宽度约束，以确保其值与PreferredMaxLayoutWidth完全相同：

message.widthAnchor.constraint(equalToConstant: frame.width * 0.5).isActive = true
message.centerXAnchor.constraint(equalTo: layoutGuide.centerXAnchor).isActive = true

Answer 1

您正在设置相对于其他视图的约束。如果其他视图的高度固定，则我不希望UILabel的大小适合文本。 我将像这样设置底部和顶部约束

message.topAnchor.constraint(greaterThanOrEqualTo: imageView.bottomAnchor, constant: POP_UP.SPACING_Y).isActive = true
message.bottomAnchor.constraint(greaterThanOrEqualTo: cancel.topAnchor, constant: -POP_UP.SPACING_Y).isActive = true

请参阅：https://developer.apple.com/documentation/uikit/nslayoutanchor/1500948-constraint