UIStackView 间距在未设置 updateConstraints 时打破约束

Posted 2023-02-23

【中文标题】UIStackView 间距在未设置 updateConstraints 时打破约束

【英文标题】：UIStackView spacing breaks constraints when not in set updateConstraints

【发布时间】：2018-03-23 15:24:36

【问题描述】：

我有一个简单的ViewController 和一个名为MyView 的自定义子视图：

import UIKit

class ViewController: UIViewController 

    let myView = MyView()

    override func viewDidLoad() 
       super.viewDidLoad()
       myView.translatesAutoresizingMaskIntoConstraints = false
       view.addSubview(myView)
       myView.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: -8.0).isActive = true
       myView.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 8.0).isActive = true
       myView.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -8.0).isActive = true
   



class MyView: UIView 

    let stackView: UIStackView
    let label = UILabel()
    let label2 = UILabel()

    init() 
      stackView = UIStackView(arrangedSubviews: [label, label2])
      super.init(frame: .zero)

      stackView.axis = .vertical

      label.translatesAutoresizingMaskIntoConstraints = false
      label.text = "Label 1"
      label2.translatesAutoresizingMaskIntoConstraints = false
      label2.text = "Label 2"
      stackView.spacing = 8.0        
      addSubview(stackView)
   

   required init?(coder aDecoder: NSCoder) 
        fatalError("init(coder:) has not been implemented")
   

   override func updateConstraints() 
        super.updateConstraints()
        stackView.fillSuperview()
   

当我运行它时，我在控制台中得到以下破坏性约束：

2018-03-23 16:11:58.960493+0100 ViewWithStackView[75612:10756278] [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:0x608000280f00 'UISV-canvas-connection' UIStackView:0x7f8438e07510.top == UILabel:0x7f8438d06740'Label 1'.top   (active)>",
"<NSLayoutConstraint:0x608000280fa0 'UISV-canvas-connection' V:[UILabel:0x7f8438e07790'Label 2']-(0)-|   (active, names: '|':UIStackView:0x7f8438e07510 )>",
"<NSLayoutConstraint:0x608000280ff0 'UISV-spacing' V:[UILabel:0x7f8438d06740'Label 1']-(8)-[UILabel:0x7f8438e07790'Label 2']   (active)>",
"<NSLayoutConstraint:0x608000280550 'UIView-Encapsulated-Layout-Height' UIStackView:0x7f8438e07510.height == 0   (active)>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x608000280ff0 'UISV-spacing' V:[UILabel:0x7f8438d06740'Label 1']-(8)-[UILabel:0x7f8438e07790'Label 2']   (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.
2018-03-23 16:11:58.961737+0100 ViewWithStackView[75612:10756278] 
    [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. 
(Note: If you're seeing NSAutoresizingMaskLayoutConstraints that you don't understand, refer to the documentation for the UIView property translatesAutoresizingMaskIntoConstraints) 
(
     "<NSAutoresizingMaskLayoutConstraint:0x6080002812c0 h=--& v=--& UIStackView:0x7f8438e07510.height == 0   (active)>",
"<NSLayoutConstraint:0x608000280f00 'UISV-canvas-connection' UIStackView:0x7f8438e07510.top == UILabel:0x7f8438d06740'Label 1'.top   (active)>",
"<NSLayoutConstraint:0x608000280fa0 'UISV-canvas-connection' V:[UILabel:0x7f8438e07790'Label 2']-(0)-|   (active, names: '|':UIStackView:0x7f8438e07510 )>",
"<NSLayoutConstraint:0x608000280ff0 'UISV-spacing' V:[UILabel:0x7f8438d06740'Label 1']-(8)-[UILabel:0x7f8438e07790'Label 2']   (active)>"
)     
Will attempt to recover by breaking constraint 

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.

现在，如果我将以下行 stackView.spacing = 8.0 移动到 updateConstraints 方法，则约束不会中断。因此，以下代码可以正常工作，而不会在控制台中出现警告/错误：

import UIKit

class ViewController: UIViewController 

    let myView = MyView()

    override func viewDidLoad() 
       super.viewDidLoad()
       myView.translatesAutoresizingMaskIntoConstraints = false
       view.addSubview(myView)
       myView.bottomAnchor.constraint(equalTo: view.bottomAnchor, constant: -8.0).isActive = true
       myView.leadingAnchor.constraint(equalTo: view.leadingAnchor, constant: 8.0).isActive = true
       myView.trailingAnchor.constraint(equalTo: view.trailingAnchor, constant: -8.0).isActive = true
   



class MyView: UIView 

    let stackView: UIStackView
    let label = UILabel()
    let label2 = UILabel()

    init() 
      stackView = UIStackView(arrangedSubviews: [label, label2])
      super.init(frame: .zero)

      stackView.axis = .vertical

      label.translatesAutoresizingMaskIntoConstraints = false
      label.text = "Label 1"
      label2.translatesAutoresizingMaskIntoConstraints = false
      label2.text = "Label 2"        
      addSubview(stackView)
   

   required init?(coder aDecoder: NSCoder) 
        fatalError("init(coder:) has not been implemented")
   

   override func updateConstraints() 
        super.updateConstraints()
        stackView.fillSuperview()
        stackView.spacing = 8.0
   

为什么将 stackView.spacing = 8.0 移动到 updateConstraints 可以解决此问题/删除警告/错误？

谢谢你的解释:)

【问题讨论】：

.fillSuperview() 发生了什么？

啊抱歉，它只是将顶部、尾部、底部和前导约束设置为 0。忘记取出辅助方法。我自己发现了这个问题......忘记设置 label.translatesAutoresizingMaskIntoConstraints = false。优雅...

【参考方案1】：

看起来这是你不想要的约束

"<NSLayoutConstraint:0x608000280550 'UIView-Encapsulated-Layout-Height' UIStackView:0x7f8438e07510.height == 0   (active)>"

我会尝试的第一件事是

stackView.translatesAutoresizingMaskIntoConstraints = false

---

另外，我不知道 stackView.fillSuperview() 在做什么，但你最好给它添加约束以填充视图。

【讨论】：

抱歉，忘记取出这个辅助方法了。它将顶部、尾部、底部和前导约束设置为 0

优雅的错误...真的忘记了 stackView.translatesAutoresizingMaskIntoConstraints = false...谢谢伙计！

【参考方案2】：

在第一种情况下，stackView 的高度为零，因为您还没有为它设置框架（在 fillSuperview() 之前的 init 中），因此在 2 个标签之间设置 8 的间距会导致冲突，但是在第二个框架为零，间距为零，根据（内在内容大小），2个标签的高度为零，因此，在这种情况下不会发生冲突，然后您在updateConstraints中设置间距，但此时stackView有根据这条线 fillSuperview() 等于它的 superView 的框架，这样也顺利进行