[英]iOS UIStackView unable to simultaneously satisfy constraints if set hidden
[英]UIStackView with custom constraints - "Unable to simultaneously satisfy constraints" when changing axis
我偶然發現了UIStackView
的問題。 它與 UIStackView 及其排列的子視圖之間存在一些自定義約束的情況有關。 更改堆棧視圖的軸和自定義約束時,錯誤消息[LayoutConstraints] Unable to simultaneously satisfy constraints.
出現在控制台中。
這是一個代碼示例,您可以將其粘貼到新項目中以觀察問題:
import UIKit
public class ViewController: UIViewController {
private var stateToggle = false
private let viewA: UIView = {
let view = UIView()
view.translatesAutoresizingMaskIntoConstraints = false
view.accessibilityIdentifier = "viewA"
view.backgroundColor = .red
return view
}()
private let viewB: UIView = {
let view = UIView()
view.translatesAutoresizingMaskIntoConstraints = false
view.accessibilityIdentifier = "viewB"
view.backgroundColor = .green
return view
}()
private lazy var stackView: UIStackView = {
let stackView = UIStackView(arrangedSubviews: [viewA, viewB])
stackView.translatesAutoresizingMaskIntoConstraints = false
stackView.distribution = .fill
stackView.alignment = .fill
stackView.accessibilityIdentifier = "stackView"
return stackView
}()
private lazy var viewAOneFourthOfStackViewHightConstraint = viewA.heightAnchor.constraint(equalTo: stackView.heightAnchor, multiplier: 0.25)
private lazy var viewAOneFourthOfStackViewWidthConstraint = viewA.widthAnchor.constraint(equalTo: stackView.widthAnchor, multiplier: 0.25)
public override func viewDidLoad() {
super.viewDidLoad()
view.accessibilityIdentifier = "rootView"
view.addSubview(stackView)
NSLayoutConstraint.activate([
stackView.topAnchor.constraint(equalTo: view.safeAreaLayoutGuide.topAnchor),
stackView.leadingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.leadingAnchor),
stackView.trailingAnchor.constraint(equalTo: view.safeAreaLayoutGuide.trailingAnchor),
stackView.bottomAnchor.constraint(equalTo: view.safeAreaLayoutGuide.bottomAnchor),
])
let button = UIButton(type: .system)
button.frame = .init(x: 50, y: 50, width: 100, height: 44)
button.setTitle("toggle layout", for: .normal)
button.tintColor = .white
button.backgroundColor = .black
button.addTarget(self, action: #selector(buttonTap), for: .touchUpInside)
view.addSubview(button)
updateConstraintsBasedOnState()
}
@objc func buttonTap() {
stateToggle.toggle()
updateConstraintsBasedOnState()
}
private func updateConstraintsBasedOnState() {
switch (stateToggle) {
case true:
stackView.axis = .horizontal
viewAOneFourthOfStackViewHightConstraint.isActive = false
viewAOneFourthOfStackViewWidthConstraint.isActive = true
case false:
stackView.axis = .vertical
viewAOneFourthOfStackViewWidthConstraint.isActive = false
viewAOneFourthOfStackViewHightConstraint.isActive = true
}
}
}
在這個例子中,我們正在制作一個帶有兩個子視圖的堆棧視圖。 我們希望其中一個占據 25% 的面積 - 所以我們有實現這一目標的約束(每個方向一個),但我們需要能夠相應地切換它們。 當切換發生時(在這種情況下從垂直堆疊到水平堆疊),出現錯誤消息:
[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:0x60000089ca00 stackView.leading == UILayoutGuide:0x6000012b48c0'UIViewSafeAreaLayoutGuide'.leading (active, names: stackView:0x7fe269d07b50 )>",
"<NSLayoutConstraint:0x60000089c9b0 stackView.trailing == UILayoutGuide:0x6000012b48c0'UIViewSafeAreaLayoutGuide'.trailing (active, names: stackView:0x7fe269d07b50 )>",
"<NSLayoutConstraint:0x60000089c730 viewA.width == 0.25*stackView.width (active, names: viewA:0x7fe269e14fd0, stackView:0x7fe269d07b50 )>",
"<NSLayoutConstraint:0x6000008ba990 'UISV-canvas-connection' stackView.leading == viewA.leading (active, names: stackView:0x7fe269d07b50, viewA:0x7fe269e14fd0 )>",
"<NSLayoutConstraint:0x6000008ba9e0 'UISV-canvas-connection' H:[viewA]-(0)-| (active, names: stackView:0x7fe269d07b50, viewA:0x7fe269e14fd0, '|':stackView:0x7fe269d07b50 )>",
"<NSLayoutConstraint:0x6000008bab20 'UIView-Encapsulated-Layout-Width' rootView.width == 375 (active, names: rootView:0x7fe269c111a0 )>",
"<NSLayoutConstraint:0x60000089ce60 'UIViewSafeAreaLayoutGuide-left' H:|-(0)-[UILayoutGuide:0x6000012b48c0'UIViewSafeAreaLayoutGuide'](LTR) (active, names: rootView:0x7fe269c111a0, '|':rootView:0x7fe269c111a0 )>",
"<NSLayoutConstraint:0x60000089cdc0 'UIViewSafeAreaLayoutGuide-right' H:[UILayoutGuide:0x6000012b48c0'UIViewSafeAreaLayoutGuide']-(0)-|(LTR) (active, names: rootView:0x7fe269c111a0, '|':rootView:0x7fe269c111a0 )>"
)
Will attempt to recover by breaking constraint
<NSLayoutConstraint:0x6000008ba990 'UISV-canvas-connection' stackView.leading == viewA.leading (active, names: stackView:0x7fe269d07b50, viewA:0x7fe269e14fd0 )>
注意約束: "<NSLayoutConstraint:0x6000008ba9e0 'UISV-canvas-connection' H:[viewA]-(0)-| (active, names: stackView:0x7fe269d07b50, viewA:0x7fe269e14fd0, '|':stackView:0x7fe269d07b50 )>"
其中說“viewA 的尾隨應與堆棧視圖的尾隨相同” 。 這不是水平軸布局的有效約束。 但這不是我添加的約束,它是堆棧視圖 ( UISV-canvas-connection
) 的內部內容。
在我看來,因為我們正在激活/停用自定義約束,並且堆棧視圖在切換軸時在內部執行相同的操作 - 暫時存在沖突和錯誤。
潛在的解決方案/解決方法:
priority = 999
。 這不是一個好的解決方法 - 不僅因為它是 hacky,而且因為在某些情況下它會導致其他布局問題(例如,當 viewA 有一些內部布局要求沖突時,例如子視圖需要擁抱優先級)。UIStackView
- 使用常規UIView
作為容器實施,並根據需要創建所需的約束。如果這應該被視為一個錯誤(並報告給 Apple)以及是否有其他(更好的?)解決方案,有什么想法嗎?
例如,有沒有辦法告訴 AutoLayout -“我將要更改一些約束以及堆棧視圖的軸 - 等我完成后再繼續評估布局”。
正如我所見,您和 iOS 都有需要停用和激活的約束。 為了正確執行並避免沖突,您和 iOS 都需要先停用舊約束,然后才能開始激活新約束。
這是一個有效的解決方案。 停用舊約束后,告訴stackView
layoutIfNeeded()
。 然后它將按順序獲得其約束,您可以激活新約束。
private func updateConstraintsBasedOnState() {
switch (stateToggle) {
case true:
stackView.axis = .horizontal
viewAOneFourthOfStackViewHightConstraint.isActive = false
stackView.layoutIfNeeded()
viewAOneFourthOfStackViewWidthConstraint.isActive = true
case false:
stackView.axis = .vertical
viewAOneFourthOfStackViewWidthConstraint.isActive = false
stackView.layoutIfNeeded()
viewAOneFourthOfStackViewHightConstraint.isActive = true
}
}
雖然vacawama的答案可以完成這項工作,但還有兩個選擇......
1 - 給約束一個小於.required
的優先級,以允許自動布局暫時打破約束而無需抱怨。
在viewDidLoad()
中添加:
viewAOneFourthOfStackViewHightConstraint.priority = .defaultHigh
viewAOneFourthOfStackViewWidthConstraint.priority = .defaultHigh
並保留原來的updateConstraintsBasedOnState()
,或者
2 - 使用不同的優先級,並交換它們而不是停用/激活約束。
在viewDidLoad()
中添加:
viewAOneFourthOfStackViewHightConstraint.priority = .defaultHigh
viewAOneFourthOfStackViewWidthConstraint.priority = .defaultLow
viewAOneFourthOfStackViewHightConstraint.isActive = true
viewAOneFourthOfStackViewWidthConstraint.isActive = true
並將updateConstraintsBasedOnState()
更改為:
private func updateConstraintsBasedOnState() {
switch (stateToggle) {
case true:
stackView.axis = .horizontal
viewAOneFourthOfStackViewHightConstraint.priority = .defaultLow
viewAOneFourthOfStackViewWidthConstraint.priority = .defaultHigh
case false:
stackView.axis = .vertical
viewAOneFourthOfStackViewWidthConstraint.priority = .defaultLow
viewAOneFourthOfStackViewHightConstraint.priority = .defaultHigh
}
}
我不知道改變優先級是否比改變激活更有效或更不有效? 但可能是需要考慮的事情。
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