晚上，
我建立了带有动态单元格的UICollectionView，因此高度可以根据内部内容进行调整。集合视图由左侧的个人资料图片，用户名，商品标题和旁边的选定注释组成。
我通过遵循教程，阅读文章并在Stack Overflow上来回往返来完成所有这些工作。但是，在调试日志中，我看到了一些关于约束的抱怨，而且我似乎无法弄清为什么它们首先出现。
我根据所有固定或可变值设置单元格的高度：用户名标签的高度（固定），标题标签的高度（可变）和注释的高度（也可变）。我在collectionView sizeForItemAt方法中执行此操作，如下所示：
let dummyTitle = "The title of my item, which can also be very long so I am wondering what will happen now"
let dummyText = "This is a long text which should automatically adapt inside the cell and then the cell height should also adapt so everything is nice and visible."
let rectWidth = view.frame.width - 32 - 60 - 16
let rect = NSString(string: dummyText).boundingRect(with:CGSize(width: rectWidth, height: 1000), options: NSStringDrawingOptions.usesFontLeading.union(NSStringDrawingOptions.usesLineFragmentOrigin), attributes: [NSAttributedStringKey.font: UIFont.systemFont(ofSize: 16)], context: nil)
let rectTitle = NSString(string: dummyTitle).boundingRect(with:CGSize(width: rectWidth, height: 1000), options: NSStringDrawingOptions.usesFontLeading.union(NSStringDrawingOptions.usesLineFragmentOrigin), attributes: [NSAttributedStringKey.font: UIFont.boldSystemFont(ofSize: 16)], context: nil)
let variableHeight = 16 + 20 + 2 + 2 + 16 + 1 + rect.height + rectTitle.height
return CGSize(width: view.frame.width, height: variableHeight)
基本上，我通过重新创建一个矩形来计算两个变量（标题标签和注释）的高度，然后获取它们的高度。为了使单元格的高度可变，我在顶部，左侧和右侧设置了约束，以便底部可以是动态的：
// horizontal constraints profile pic & username
addConstraintsWithFormat(format: "H:|-16-[v0(60)]-16-[v1]-16-|", views: profilePictureImageView, usernameLabel)
// horizontal constraints title
addConstraintsWithFormat(format: "H:|-92-[v0]-16-|", views: titleLabel)
// horizontal constraints comment
addConstraintsWithFormat(format: "H:|-92-[v0]-16-|", views: commentTextView)
// vertical constraints profile pic & separator
addConstraintsWithFormat(format: "V:|-16-[v0(60)]-16-[v1(1)]|", views: profilePictureImageView, separatorView)
// horizontal constraints separator
addConstraintsWithFormat(format: "H:|[v0]|", views: separatorView)
// vertical constraints username
addConstraintsWithFormat(format: "V:|-16-[v0(20)]-2-|", views: usernameLabel)
// top constraints workout
addConstraints([NSLayoutConstraint(item: titleLabel, attribute: .top, relatedBy: .equal, toItem: usernameLabel, attribute: .bottom, multiplier: 1, constant: 2)])
// top constraint comment
addConstraints([NSLayoutConstraint(item: commentTextView, attribute: .top, relatedBy: .equal, toItem: titleLabel, attribute: .bottom, multiplier: 1, constant: 2)])
该应用程序可以正常运行并显示相应的所有内容，但是我想进行一个干净的调试，因为恐怕以后可能会引起问题。我还想了解为什么首先会发生此错误，所以我可以在以后的项目中避免它。
编辑：添加了调试日志的一部分。这是13个错误中的两个：
2018-09-16 16:20:30.030871+0200 prjExplanation[12946:529268] [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.
(
"<NSLayoutConstraint:0x6040002810e0 V:|-(16)-[UIImageView:0x7fe8b2f1dd00] (active, names: '|':prjExplanation.socialCell:0x7fe8b2c1c970 )>",
"<NSLayoutConstraint:0x604000281360 UIImageView:0x7fe8b2f1dd00.height == 60 (active)>",
"<NSLayoutConstraint:0x6040002816d0 V:[UIImageView:0x7fe8b2f1dd00]-(16)-[UIView:0x7fe8b2c21a70] (active)>",
"<NSLayoutConstraint:0x604000281680 UIView:0x7fe8b2c21a70.height == 1 (active)>",
"<NSLayoutConstraint:0x6040002811d0 V:[UIView:0x7fe8b2c21a70]-(0)-| (active, names: '|':prjExplanation.socialCell:0x7fe8b2c1c970 )>",
"<NSLayoutConstraint:0x604000281310 V:|-(16)-[UILabel:0x7fe8b2f1e4f0'Author_203'] (active, names: '|':prjExplanation.socialCell:0x7fe8b2c1c970 )>",
"<NSLayoutConstraint:0x60400009f8b0 UILabel:0x7fe8b2f1e4f0'Author_203'.height == 20 (active)>",
"<NSLayoutConstraint:0x60400009c430 V:[UILabel:0x7fe8b2f1e4f0'Author_203']-(2)-| (active, names: '|':prjExplanation.socialCell:0x7fe8b2c1c970 )>"
)
Will attempt to recover by breaking constraint
<NSLayoutConstraint:0x6040002816d0 V:[UIImageView:0x7fe8b2f1dd00]-(16)-[UIView:0x7fe8b2c21a70] (active)>
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.
2018-09-16 16:20:30.043291+0200 prjExplanation[12946:529268] [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.
(
"<NSLayoutConstraint:0x6040002820d0 V:|-(16)-[UIImageView:0x7fe8b2f274a0] (active, names: '|':prjExplanation.socialCell:0x7fe8b2f26bc0 )>",
"<NSLayoutConstraint:0x604000281ea0 UIImageView:0x7fe8b2f274a0.height == 60 (active)>",
"<NSLayoutConstraint:0x604000282300 V:[UIImageView:0x7fe8b2f274a0]-(16)-[UIView:0x7fe8b2d0b880] (active)>",
"<NSLayoutConstraint:0x604000282120 UIView:0x7fe8b2d0b880.height == 1 (active)>",
"<NSLayoutConstraint:0x604000281d60 V:[UIView:0x7fe8b2d0b880]-(0)-| (active, names: '|':prjExplanation.socialCell:0x7fe8b2f26bc0 )>",
"<NSLayoutConstraint:0x6040002823f0 V:|-(16)-[UILabel:0x7fe8b2f276d0'Author_203'] (active, names: '|':prjExplanation.socialCell:0x7fe8b2f26bc0 )>",
"<NSLayoutConstraint:0x6040002823a0 UILabel:0x7fe8b2f276d0'Author_203'.height == 20 (active)>",
"<NSLayoutConstraint:0x604000281ef0 V:[UILabel:0x7fe8b2f276d0'Author_203']-(2)-| (active, names: '|':prjExplanation.socialCell:0x7fe8b2f26bc0 )>"
)
Will attempt to recover by breaking constraint
<NSLayoutConstraint:0x604000282300 V:[UIImageView:0x7fe8b2f274a0]-(16)-[UIView:0x7fe8b2d0b880] (active)>
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.