不在 set updateConstraints 中时，UIStackView 间距会打破约束
UIStackView spacing breaks constraints when not in set updateConstraints
我有一个简单的 ViewController，带有一个名为 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 这样做时，我在控制台中得到以下打破约束：
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，如果我将下面的行 stackView.spacing = 8.0 移动到 updateConstraints 方法，约束将不会中断。因此，以下代码在控制台中没有警告/错误的情况下工作正常：
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 可以解决这个问题/删除警告/错误？
感谢您的解释:)
在第一种情况下，stackView 的高度为零，因为您尚未为其设置框架（在 fillSuperview() 之前的 init 中），因此在 2 个标签之间设置 8 的间距会引起冲突，但在第二个框架为零，间距为零，根据（内在内容大小），2个标签的高度将为零，因此，在这种情况下不会发生冲突，然后将间距设置为 updateConstraints 但在那一刻 stackView 的框架等于它的 superView 根据这条线 fillSuperview() 所以也很顺利
看起来这是你不想要的约束
"<NSLayoutConstraint:0x608000280550 'UIView-Encapsulated-Layout-Height' UIStackView:0x7f8438e07510.height == 0 (active)>"
我首先要尝试的是
stackView.translatesAutoresizingMaskIntoConstraints = false
此外，我不知道 stackView.fillSuperview() 在做什么，但您最好为其添加约束以填充视图。
我有一个简单的 ViewController，带有一个名为 MyView:
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 这样做时，我在控制台中得到以下打破约束：
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，如果我将下面的行 stackView.spacing = 8.0 移动到 updateConstraints 方法，约束将不会中断。因此，以下代码在控制台中没有警告/错误的情况下工作正常：
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 可以解决这个问题/删除警告/错误？
感谢您的解释:)
在第一种情况下，stackView 的高度为零，因为您尚未为其设置框架（在 fillSuperview() 之前的 init 中），因此在 2 个标签之间设置 8 的间距会引起冲突，但在第二个框架为零，间距为零，根据（内在内容大小），2个标签的高度将为零，因此，在这种情况下不会发生冲突，然后将间距设置为 updateConstraints 但在那一刻 stackView 的框架等于它的 superView 根据这条线 fillSuperview() 所以也很顺利
看起来这是你不想要的约束
"<NSLayoutConstraint:0x608000280550 'UIView-Encapsulated-Layout-Height' UIStackView:0x7f8438e07510.height == 0 (active)>"
我首先要尝试的是
stackView.translatesAutoresizingMaskIntoConstraints = false
此外，我不知道 stackView.fillSuperview() 在做什么，但您最好为其添加约束以填充视图。