Swift - 从 UICollectionViewCell 内的视图中删除约束
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【中文标题】Swift - 从 UICollectionViewCell 内的视图中删除约束【英文标题】:Swift - Remove constraints from a view inside a UICollectionViewCell 【发布时间】:2020-07-20 22:14:34 【问题描述】:我以编程方式在自定义 UICollectionViewCell
内的视图中添加了一些约束,但我注意到当一个单元格被重用时,可能会重新添加约束。
这是正在记录的内容:
> Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints
> to catch this in the debugger. The methods in the
> UIConstraintBasedLayoutDebugging category on UIView listed in
> <UIKitCore/UIView.h> may also be helpful. 2020-07-21
> 01:00:10.466637+0300 AutoLayout Message Cells[5227:336361]
> [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:0x600000435090 AutoLayout_Message_Cells.MessageCollectionViewCell:0x7fbd76e24670.height
> == UIView:0x7fbd76e291b0.height (active)>",
> "<NSLayoutConstraint:0x6000004350e0 V:|-(8)-[UILabel:0x7fbd76e29510'UOA'] (active, names:
> '|':UIView:0x7fbd76e291b0 )>",
> "<NSLayoutConstraint:0x6000004351d0 UILabel:0x7fbd76e29510'UOA'.height == 30 (active)>",
> "<NSLayoutConstraint:0x600000435220 V:[UILabel:0x7fbd76e29510'UOA']-(-12)-[UILabel:0x7fbd76e29790'2h']
> (active)>",
> "<NSLayoutConstraint:0x600000435310 UILabel:0x7fbd76e29790'2h'.height == 30 (active)>",
> "<NSLayoutConstraint:0x6000004353b0 V:[UILabel:0x7fbd76e29790'2h']-(16)-[UITextView:0x7fbd7805b200'Lorem
> ipsum dolor sit ame...'] (active)>",
> "<NSLayoutConstraint:0x600000435400 UITextView:0x7fbd7805b200'Lorem ipsum dolor sit ame...'.bottom ==
> UIView:0x7fbd76e291b0.bottom - 1 (active)>",
> "<NSLayoutConstraint:0x60000042a990 'UIView-Encapsulated-Layout-Height'
> AutoLayout_Message_Cells.MessageCollectionViewCell:0x7fbd76e24670.height
> == 50 (active)>" )
这是我手机的代码:
import UIKit
class MessageCollectionViewCell: UICollectionViewCell
@IBOutlet var textView: UITextView!
@IBOutlet var schoolLabel: UILabel!
@IBOutlet var dateLabel: UILabel!
override func awakeFromNib()
super.awakeFromNib()
setupConstraints()
fileprivate func setupConstraints()
setupCellConstraints()
setupSchoolLabelConstraints()
setupDateLabelConstraints()
setupTextViewConstraints()
fileprivate func setupCellConstraints()
self.contentView.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
self.contentView.widthAnchor.constraint(equalToConstant: UIScreen.main.bounds.width - (self.frame.origin.x * 2))
])
NSLayoutConstraint.activate([
self.widthAnchor.constraint(equalTo: self.contentView.widthAnchor),
self.heightAnchor.constraint(equalTo: self.contentView.heightAnchor)
])
fileprivate func setupSchoolLabelConstraints()
schoolLabel.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
schoolLabel.topAnchor.constraint(equalTo: self.contentView.topAnchor, constant: 8),
schoolLabel.leadingAnchor.constraint(equalTo: self.contentView.leadingAnchor, constant: 8),
schoolLabel.trailingAnchor.constraint(equalTo: self.contentView.centerXAnchor, constant: 60),
schoolLabel.heightAnchor.constraint(equalToConstant: 30)
])
fileprivate func setupDateLabelConstraints()
dateLabel.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
dateLabel.topAnchor.constraint(equalTo: schoolLabel.bottomAnchor, constant: -12),
dateLabel.leadingAnchor.constraint(equalTo: self.contentView.leadingAnchor, constant: 8),
dateLabel.trailingAnchor.constraint(equalTo: self.contentView.centerXAnchor, constant: 60),
dateLabel.heightAnchor.constraint(equalToConstant: 30)
])
fileprivate func setupTextViewConstraints()
textView.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
textView.topAnchor.constraint(equalTo: dateLabel.bottomAnchor, constant: 16),
textView.bottomAnchor.constraint(equalTo: self.contentView.bottomAnchor, constant: -1),
textView.leadingAnchor.constraint(equalTo: self.contentView.leadingAnchor, constant: 8),
textView.trailingAnchor.constraint(lessThanOrEqualTo: self.contentView.centerXAnchor, constant: 60)
])
有没有办法在重新添加之前清除所有约束?
【问题讨论】:
这是唯一的出路?我不认为保留对约束的引用是最好的...... 好的,我刚刚查看了您的约束,它们本身就是错误的。 我刚刚开始使用 AutoLayout,所以您可能是对的!我做错了什么? 只需在storyboard中配置约束即可。并且不要约束单元格或内容视图。删除所有代码。 我正在限制单元格的宽度,以便它可以根据textView
s 文本具有动态高度
【参考方案1】:
我也以编程方式而不是在情节提要中使用约束。您遇到的问题是某些约束不能共存。
例如在代码中我没有看到:
> "<NSLayoutConstraint:0x60000042a990 'UIView-Encapsulated-Layout-Height'
> AutoLayout_Message_Cells.MessageCollectionViewCell:0x7fbd76e24670.height
> == 50 (active)>" )
某处(可能在故事板中?)您给出的高度为 50,但是:
单元格与 contentView 的高度相同:
self.heightAnchor.constraint(equalTo: self.contentView.heightAnchor)
在您提供的单元格中:
schoolLabel.topAnchor.constraint(equalTo: self.contentView.topAnchor, constant: 8),
....
schoolLabel.heightAnchor.constraint(equalToConstant: 30)
所以我们有 8 个形式的内容顶部 + 30 个高度 (38),那么:
dateLabel.topAnchor.constraint(equalTo: schoolLabel.bottomAnchor, constant: -12),
....
dateLabel.heightAnchor.constraint(equalToConstant: 30)
您返回 12,然后再次返回 30 (38 - 12 + 30 = 56) 的高度。 我们超出了 50 个单元格,再加上您添加的文本:
textView.topAnchor.constraint(equalTo: dateLabel.bottomAnchor, constant: 16),
textView.bottomAnchor.constraint(equalTo: self.contentView.bottomAnchor, constant: -1)
其高度将导致负数(textView 顶部为 56 + 16 = 72,但底部为 50(我们看不到的约束)- 1 = 49 --> 它的高度为 -23
【讨论】:
那我该怎么办?我检查了,我没有为项目中任何地方的单元格指定高度 50 我应该从标签中删除高度并运行它,检查会发生什么。消息说'AutoLayout_Message_Cells',所以它可能有点奇怪..就像你决定在视图中有X行并创建它们它创建50高度的约束。或者您可以为内容视图指定高度 80(或准确地说是 72),然后查看错误是否再次出现。以上是关于Swift - 从 UICollectionViewCell 内的视图中删除约束的主要内容,如果未能解决你的问题,请参考以下文章
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