Swift以编程方式添加的约束不起作用 [英] Swift programmatically-added constraints dont work
问题描述
我在滚动视图中有一个视图：
I have a view inside a scrollview:
现在，我想以编程方式将子视图添加到该视图。多数民众赞成在我的代码中做到这一点：
Now I want to add the child views to that view programmatically. Thats my code to do that:
-
子视图（有效）
Child view (works)
//Adds header to the view again because it was removed in the clear() method
//Header is just a label
lv.addSubview(header)
header.leadingAnchor.constraint(equalTo: header.superview!.leadingAnchor).isActive = true
header.topAnchor.constraint(equalTo: header.superview!.topAnchor, constant: 2).isActive = true
header.widthAnchor.constraint(equalTo: header.superview!.widthAnchor).isActive = true
header.heightAnchor.constraint(equalToConstant: MainTabViewController.fontSize*3).isActive = true //Just a constant
现在我重复执行此代码：
Now I execute this code repeatedly:
private func makeTextLabel(text: NSAttributedString, bgColor: UIColor?, maxWidth: CGFloat?) -> UILabel {
//Creates label
let label = UILabel()
label.translatesAutoresizingMaskIntoConstraints = false
lv.addSubview(label)
//Adjustments
if(bgColor != nil) {
label.backgroundColor = bgColor
}
label.textColor = UIColor.black
label.attributedText = text
label.numberOfLines = 0
label.lineBreakMode = NSLineBreakMode.byWordWrapping
let width = maxWidth ?? lv.frame.size.width-8
label.widthAnchor.constraint(equalToConstant: width).isActive = true
label.heightAnchor.constraint(equalToConstant: heightForLabel(attributedText: label.attributedText, width: width)).isActive = true
label.leadingAnchor.constraint(equalTo: lv.leadingAnchor, constant: 4).isActive = true
let previousView = lv.subviews[lv.subviews.count-1]
label.topAnchor.constraint(equalTo: previousView.bottomAnchor, constant: 10).isActive = true
return label
}
所有标签都已添加，但约束根本不起作用。这是什么样子（当我执行两次以上方法时）：
All the labels are added, but the constraints dont work at all. Here is what is looks like (when I execute the method above 2 times):
编辑：解决了主要问题。我现在正在使用StackView。（ https://stackoverflow.com/a/59828434/6257435 ）
The main problem is solved. I am using a StackView now.(https://stackoverflow.com/a/59828434/6257435)
我现在希望我的标签的边缘偏移，所以我使用这些线：
I now want my labels to have an offset to the edges, so I use those lines:
label.leadingAnchor.constraint(equalTo: lessonStackView.leadingAnchor, constant: offset).isActive = true
label.trailingAnchor.constraint(equalTo: lessonStackView.trailingAnchor, constant: -offset).isActive = true
但是当StackView似乎设置了x约束本身时，我得到了这个警告：
But as the StackView seems to set x-constraints itself, I get this warning:
无法同时满足约束条件。
以下列表中的约束中至少有一个是您不想要的约束。
尝试一下：
（1）查看每个约束，并尝试找出不期望的约束；
（2）查找添加了一个或多个不需要的约束的代码并进行修复。
（
UILabel：0x7f9c16c22c30'Falls dir die App gef\U00e4llt ...'（活动，名称：'|'：JavaProf.MultipleContentsView：0x7f9c19024a60）>，
，
）
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. ( "UILabel:0x7f9c16c22c30'Falls dir die App gef\U00e4llt...' (active, names: '|':JavaProf.MultipleContentsView:0x7f9c19024a60 )>", "", "" )
将尝试通过打破约束
来恢复
Will attempt to recover by breaking constraint
我该如何解决？
推荐答案
删除 width 锚点。您不必在意宽度（而且您也不是很清楚），而是使用 trailingAnchor 来代替：
Remove width anchor. You should not care about width (and you don't really know it), use trailingAnchor instead:
label.trailingAnchor.constraint(equalTo: lv.trailingAnchor, constant: -4).isActive = true
删除 heightAnchor ，而是让系统为您计算高度：
Remove heightAnchor, instead let system calculate the height for you:
label.setContentHuggingPriority(.required, for: .vertical)
label.setContentCompressionResistancePriority(.required, for: .vertical)
这应该是所有必需的。
但是，作为一个补充说明，而不是对前一个标签创建约束，您可以只使用 UIStackView 。
However, as a side note, instead of creating a constraint to previous label, you could just use a UIStackView.
这篇关于Swift以编程方式添加的约束不起作用的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
