如何为具有动态高度的表格单元格正确设置自动布局? [英] How to set auto layout correctly for a table cell with dynamic height?

问题描述

我尝试创建一个 UITableViewCell 并设置子视图如下:

I try to create a UITableViewCell and setup subviews as below:

class MyCellView: UITableViewCell {

    private let ImageView = UIImageView()
    private let titleView = UILabel()

    override init(style: UITableViewCellStyle, reuseIdentifier: String?) {

        super.init(style: style, reuseIdentifier: reuseIdentifier)

        contentView.addSubview(ImageView)
        contentView.addSubview(titleView)

        ImageView.translatesAutoresizingMaskIntoConstraints = false
        ImageView.topAnchor.constraint(equalTo: contentView.topAnchor).isActive = true
        ImageView.leftAnchor.constraint(equalTo: contentView.leftAnchor).isActive = true
        ImageView.rightAnchor.constraint(equalTo: contentView.rightAnchor).isActive = true
        ImageView.heightAnchor.constraint(equalTo: contentView.widthAnchor, multiplier: 0.6).isActive = true

        titleView.translatesAutoresizingMaskIntoConstraints = false
        titleView.topAnchor.constraint(equalTo: ImageView.bottomAnchor).isActive = true
        titleView.leftAnchor.constraint(equalTo: contentView.leftAnchor).isActive = true
        titleView.rightAnchor.constraint(equalTo: contentView.rightAnchor).isActive = true
        titleView.bottomAnchor.constraint(equalTo: contentView.bottomAnchor).isActive = true

        titleView.numberOfLines = 0

        titleView.text = " "   // <-- *** please note this line

    }
}

在表格视图中，我已将其设置为使用动态高度:

And in the table view, I have set it to use dynamic height:

tableView.estimatedRowHeight = 80
tableView.rowHeight = UITableViewAutomaticDimension

我的问题是如果我没有在单元格中为 titleView 设置文本，例如如果我在单元格视图中注释最后一行:

My question is if I don't set the text for titleView in the cell, such as if I remark the last line in the cell view:

// titleView.text = " "

我将从 XCode 收到约束错误.但是如果我设置文本，一切正常.

I will get constraint error from XCode. But if I set the text, everything works fine.

文本是从网上动态下载的，所以文本可能是空的.另外我可以将文本设置为""，一个空格，不知道我在这里误解了什么?如果我更正某些内容，文本可以为空("" 或 nil)吗?

The text is dynamically downloaded from the Internet, so the text might be empty. Besides I can just set the text to " ", an empty space, I wonder if I misunderstand anything here? Can the text be empty ("" or nil) if I correct something?

同样，如果我完全删除关于 titleView 的代码，我只想在单元格中有一个 UIImageView，我发现单元格的高度没有扩展.如何设置它以便我可以在单元格中获得动态高度的图像?

Similarly, if I remove the code about titleView entirely, I just want to have an UIImageView in the cell, I found the cell's height is not expanded. How to set it up so that I can have an image of dynamic height in the cell?

约束错误:

2017-12-22 15:35:34.715865+0800 MyProject[15774:733515] [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:0x60c000095450 V:|-(0)-[UIImageView:0x7ff40df0de90]   (active, names: '|':UITableViewCellContentView:0x7ff40df0edc0 )>",
"<NSLayoutConstraint:0x60c0000955e0 UIImageView:0x7ff40df0de90.height == 0.6*UITableViewCellContentView:0x7ff40df0edc0.width   (active)>",
"<NSLayoutConstraint:0x60c000095630 V:[UIImageView:0x7ff40df0de90]-(0)-[UILabel:0x7ff40df0e0c0]   (active)>",
"<NSLayoutConstraint:0x60c0000957c0 UILabel:0x7ff40df0e0c0.bottom == UITableViewCellContentView:0x7ff40df0edc0.bottom   (active)>",
"<NSLayoutConstraint:0x60c000096210 'UIView-Encapsulated-Layout-Height' UITableViewCellContentView:0x7ff40df0edc0.height == 248.333   (active)>",
"<NSLayoutConstraint:0x60c000095ea0 'UIView-Encapsulated-Layout-Width' UITableViewCellContentView:0x7ff40df0edc0.width == 414   (active)>"
)

Will attempt to recover by breaking constraint
<NSLayoutConstraint:0x60c000095630 V:[UIImageView:0x7ff40df0de90]-(0)-[UILabel:0x7ff40df0e0c0]   (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.

推荐答案

• 如果你想避免警告，试试下面的代码

  • If you want to avoid warning, try the code below

    class MyCellView: UITableViewCell {
    
      private let ImageView = UIImageView()
      private let titleView = UILabel()
    
      override init(style: UITableViewCellStyle, reuseIdentifier: String?) {
    
        super.init(style: style, reuseIdentifier: reuseIdentifier)
    
        contentView.addSubview(ImageView)
        contentView.addSubview(titleView)
    
        ImageView.translatesAutoresizingMaskIntoConstraints = false
        ImageView.topAnchor.constraint(equalTo: contentView.topAnchor).isActive = true
        ImageView.leftAnchor.constraint(equalTo: contentView.leftAnchor).isActive = true
        ImageView.rightAnchor.constraint(equalTo: contentView.rightAnchor).isActive = true
        let heightConstraint = ImageView.heightAnchor.constraint(equalTo: contentView.widthAnchor, multiplier: 0.6)
        heightConstraint.priority = UILayoutPriority.defaultLow
        heightConstraint.isActive = true
    
        titleView.translatesAutoresizingMaskIntoConstraints = false
        titleView.topAnchor.constraint(equalTo: ImageView.bottomAnchor).isActive = true
        titleView.leftAnchor.constraint(equalTo: contentView.leftAnchor).isActive = true
        titleView.rightAnchor.constraint(equalTo: contentView.rightAnchor).isActive = true
        titleView.bottomAnchor.constraint(equalTo: contentView.bottomAnchor).isActive = true
    
        titleView.numberOfLines = 0
    
    //    titleView.text = " "
      }
    }
    

  • 如果您完全删除了关于 titleView 的代码，并希望在单元格中有一个具有动态高度的 UIImageView，请添加 bottomAnchorimageView

  • If you remove the code about titleView entirely and want to have an UIImageView with dynamic height in the cell, adding bottomAnchor constraint for imageView

    class MyCellView: UITableViewCell {
    
      private let ImageView = UIImageView()
      private let titleView = UILabel()
    
      override init(style: UITableViewCellStyle, reuseIdentifier: String?) {
    
        super.init(style: style, reuseIdentifier: reuseIdentifier)
    
        contentView.addSubview(ImageView)
        contentView.addSubview(titleView)
    
        ImageView.translatesAutoresizingMaskIntoConstraints = false
        ImageView.topAnchor.constraint(equalTo: contentView.topAnchor).isActive = true
        ImageView.leftAnchor.constraint(equalTo: contentView.leftAnchor).isActive = true
        ImageView.bottomAnchor.constraint(equalTo: contentView.bottomAnchor).isActive = true
        ImageView.rightAnchor.constraint(equalTo: contentView.rightAnchor).isActive = true
        let heightConstraint = ImageView.heightAnchor.constraint(equalTo: contentView.widthAnchor, multiplier: 0.6)
        heightConstraint.priority = UILayoutPriority.defaultLow
        heightConstraint.isActive = true
      }
    }
    

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