我的自动布局约束有什么问题？

Question

这是我按下按钮之前的 UIViewController（我没有把它放在那里，因为它不相关）：

当我按下按钮时，一个包含两个 UIPickerView 的 UIView 从顶部出现。在这个 UIView 的正下方是 2 个 UIButton。一切都适用于自动布局：

这是我创建约束时的代码：

let okButtonHeight: CGFloat = 53
let okButtonWidth: CGFloat = 53
let leftPickerViewWidth: CGFloat = 80
let leftPickerViewHeight: CGFloat = 200
let margin: CGFloat = 8

// frame
let constraint0 = NSLayoutConstraint(item: okButton, attribute: .Bottom, relatedBy: .Equal, toItem: self.view, attribute: .Top, multiplier: 1, constant: 0)
let constraint1 = NSLayoutConstraint(item: frameView, attribute: .CenterX, relatedBy: .Equal, toItem: view, attribute: .CenterX, multiplier: 1, constant: 0)

// left & right pickerViews
let constraint2 = NSLayoutConstraint(item: leftPickerView, attribute: .Width, relatedBy: .Equal, toItem: rightPickerView, attribute: .Width, multiplier: 1, constant: 0)
let constraint3 = NSLayoutConstraint(item: leftPickerView, attribute: .Height, relatedBy: .Equal, toItem: rightPickerView, attribute: .Height, multiplier: 1, constant: 0)
let constraint4 = NSLayoutConstraint(item: leftPickerView, attribute: .Trailing, relatedBy: .Equal, toItem: rightPickerView, attribute: .Leading, multiplier: 1, constant: -margin)
let constraint5 = NSLayoutConstraint(item: leftPickerView, attribute: .Top, relatedBy: .Equal, toItem: rightPickerView, attribute: .Top, multiplier: 1, constant: 0)

// left pickerView
let constraint6 = NSLayoutConstraint(item: leftPickerView, attribute: .Height, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 1, constant: leftPickerViewHeight)
let constraint7 = NSLayoutConstraint(item: leftPickerView, attribute: .Width, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 1, constant: leftPickerViewWidth)
let constraint8 = NSLayoutConstraint(item: leftPickerView, attribute: .Top, relatedBy: .Equal, toItem: frameView, attribute: .Top, multiplier: 1, constant: -margin)
let constraint9 = NSLayoutConstraint(item: leftPickerView, attribute: .Bottom, relatedBy: .Equal, toItem: frameView, attribute: .Bottom, multiplier: 1, constant: margin)
let constraint10 = NSLayoutConstraint(item: leftPickerView, attribute: .Leading, relatedBy: .Equal, toItem: frameView, attribute: .Leading, multiplier: 1, constant: margin)

// right pickerView
let constraint11 = NSLayoutConstraint(item: rightPickerView, attribute: .Trailing, relatedBy: .Equal, toItem: frameView, attribute: .Trailing, multiplier: 1, constant: -margin)

// ok & cancel buttons
let constraint12 = NSLayoutConstraint(item: okButton, attribute: .Top, relatedBy: .Equal, toItem: cancelButton, attribute: .Top, multiplier: 1, constant: 0)
let constraint13 = NSLayoutConstraint(item: okButton, attribute: .Bottom, relatedBy: .Equal, toItem: cancelButton, attribute: .Bottom, multiplier: 1, constant: 0)
let constraint14 = NSLayoutConstraint(item: okButton, attribute: .Width, relatedBy: .Equal, toItem: cancelButton, attribute: .Width, multiplier: 1, constant: 0)
let constraint15 = NSLayoutConstraint(item: okButton, attribute: .Height, relatedBy: .Equal, toItem: cancelButton, attribute: .Height, multiplier: 1, constant: 0)

// ok button
let constraint16 = NSLayoutConstraint(item: view, attribute: .CenterX, relatedBy: .Equal, toItem: okButton, attribute: .Trailing, multiplier: 1, constant: 10)
let constraint17 = NSLayoutConstraint(item: okButton, attribute: .Width, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 1, constant: okButtonWidth)
let constraint18 = NSLayoutConstraint(item: okButton, attribute: .Height, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 1, constant: okButtonHeight)
let constraint19 = NSLayoutConstraint(item: okButton, attribute: .Top, relatedBy: .Equal, toItem: frameView, attribute: .Bottom, multiplier: 1, constant: 10)

// cancel button
let constraint20 = NSLayoutConstraint(item: view, attribute: .CenterX, relatedBy: .Equal, toItem: cancelButton, attribute: .Leading, multiplier: 1, constant: -10)

view.addConstraint(constraint0)
view.addConstraint(constraint1)
view.addConstraint(constraint12)
view.addConstraint(constraint13)
view.addConstraint(constraint14)
view.addConstraint(constraint15)
view.addConstraint(constraint16)
view.addConstraint(constraint17)
view.addConstraint(constraint18)
view.addConstraint(constraint19)
view.addConstraint(constraint20)

frameView.addConstraint(constraint2)
frameView.addConstraint(constraint3)
frameView.addConstraint(constraint4)
frameView.addConstraint(constraint5)
frameView.addConstraint(constraint6)
frameView.addConstraint(constraint7)
frameView.addConstraint(constraint8)
frameView.addConstraint(constraint9)
frameView.addConstraint(constraint10)
frameView.addConstraint(constraint11)

selectionCurrencyConstraintList = [constraint0, constraint1, constraint2, constraint3, constraint4, constraint5, constraint6, constraint7, constraint8, constraint9, constraint10, constraint11, constraint12, constraint13, constraint14, constraint15, constraint16, constraint17, constraint18, constraint19, constraint20]

frameView.hidden = true
okButton.hidden = true
cancelButton.hidden = true

此时，UIView 和两个按钮隐藏在屏幕顶部的正上方。

当我按下按钮使其出现时，我执行以下代码：

frameView.hidden = hide
okButton.hidden = hide
cancelButton.hidden = hide

if var constraints = selectionCurrencyConstraintList {
    let topFrameConstraint = constraints[0]
    view.removeConstraint(topFrameConstraint)
    constraints.removeAtIndex(0)
    let newTopConstraint: NSLayoutConstraint!
    if hide {
        newTopConstraint = NSLayoutConstraint(item: okButton, attribute: .Bottom, relatedBy: .Equal, toItem: self.view, attribute: .Top, multiplier: 1, constant: 0)
    } else {
        newTopConstraint = NSLayoutConstraint(item: frameView, attribute: .Top, relatedBy: .Equal, toItem: topView, attribute: .Bottom, multiplier: 1, constant: margin)
    }
    constraints.insert(newTopConstraint, atIndex: 0)
    view.addConstraint(newTopConstraint)
}

UIView.animateWithDuration(0.5) {
    self.view.layoutIfNeeded()
}

当我用这个NSLayoutConstraint(item: frameView, attribute: .Top, relatedBy: .Equal, toItem: topView, attribute: .Bottom, multiplier: 1, constant: margin) 替换这个约束NSLayoutConstraint(item: okButton, attribute: .Bottom, relatedBy: .Equal, toItem: self.view, attribute: .Top, multiplier: 1, constant: 0) 时，它工作正常。

当我反转它时，我得到了一些无法满足的约束：

2015-05-15 20:17:25.374 CurrencyEx[624:42779] 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) 
(
    "<NSLayoutConstraint:0x17408de30 V:[UIView:0x174186660(50)]>",
    "<NSLayoutConstraint:0x174090fe0 V:[_UILayoutGuide:0x1741a8a40]-(0)-[UIView:0x174186660]>",
    "<_UILayoutSupportConstraint:0x1740a3e40 V:[_UILayoutGuide:0x1741a8a40(20)]>",
    "<_UILayoutSupportConstraint:0x1740a3d80 V:|-(0)-[_UILayoutGuide:0x1741a8a40]   (Names: '|':UIView:0x174186590 )>",
    "<NSLayoutConstraint:0x170089150 V:[UIButton:0x146e49020(53)]>",
    "<NSLayoutConstraint:0x1700891a0 V:[UIView:0x1741868d0]-(10)-[UIButton:0x146e49020]>",
    "<NSLayoutConstraint:0x170088d90 V:[UIPickerView:0x146e09ef0(200)]>",
    "<NSLayoutConstraint:0x170088e30 V:|-(-8)-[UIPickerView:0x146e09ef0]   (Names: '|':UIView:0x1741868d0 )>",
    "<NSLayoutConstraint:0x170088e80 UIPickerView:0x146e09ef0.bottom == UIView:0x1741868d0.bottom + 8>",
    "<NSLayoutConstraint:0x17008ef60 V:[UIView:0x174186660]-(8)-[UIView:0x1741868d0]>",
    "<NSLayoutConstraint:0x174096620 UIButton:0x146e49020.bottom == UIView:0x174186590.top>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x170088e80 UIPickerView:0x146e09ef0.bottom == UIView:0x1741868d0.bottom + 8>

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.
2015-05-15 20:17:25.377 CurrencyEx[624:42779] 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) 
(
    "<NSLayoutConstraint:0x17408de30 V:[UIView:0x174186660(50)]>",
    "<NSLayoutConstraint:0x174090fe0 V:[_UILayoutGuide:0x1741a8a40]-(0)-[UIView:0x174186660]>",
    "<_UILayoutSupportConstraint:0x1740a3e40 V:[_UILayoutGuide:0x1741a8a40(20)]>",
    "<_UILayoutSupportConstraint:0x1740a3d80 V:|-(0)-[_UILayoutGuide:0x1741a8a40]   (Names: '|':UIView:0x174186590 )>",
    "<NSLayoutConstraint:0x170089150 V:[UIButton:0x146e49020(53)]>",
    "<NSLayoutConstraint:0x1700891a0 V:[UIView:0x1741868d0]-(10)-[UIButton:0x146e49020]>",
    "<NSLayoutConstraint:0x17008ef60 V:[UIView:0x174186660]-(8)-[UIView:0x1741868d0]>",
    "<NSLayoutConstraint:0x174096620 UIButton:0x146e49020.bottom == UIView:0x174186590.top>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x17408de30 V:[UIView:0x174186660(50)]>

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.
2015-05-15 20:17:25.378 CurrencyEx[624:42779] 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) 
(
    "<NSLayoutConstraint:0x174090fe0 V:[_UILayoutGuide:0x1741a8a40]-(0)-[UIView:0x174186660]>",
    "<_UILayoutSupportConstraint:0x1740a3e40 V:[_UILayoutGuide:0x1741a8a40(20)]>",
    "<_UILayoutSupportConstraint:0x1740a3d80 V:|-(0)-[_UILayoutGuide:0x1741a8a40]   (Names: '|':UIView:0x174186590 )>",
    "<NSLayoutConstraint:0x170089150 V:[UIButton:0x146e49020(53)]>",
    "<NSLayoutConstraint:0x1700891a0 V:[UIView:0x1741868d0]-(10)-[UIButton:0x146e49020]>",
    "<NSLayoutConstraint:0x17008ef60 V:[UIView:0x174186660]-(8)-[UIView:0x1741868d0]>",
    "<NSLayoutConstraint:0x174096620 UIButton:0x146e49020.bottom == UIView:0x174186590.top>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x1700891a0 V:[UIView:0x1741868d0]-(10)-[UIButton:0x146e49020]>

我不明白为什么。它最初适用于这些限制。当我修改其中一些时它可以工作，当我把它们放回去时，它就不再工作了......

有什么想法吗？

Answer 1

让我们调用你的约束：

ConstraintHide:okButton 底部与超级视图顶部对齐。
ConstraintShow:frameView 比 topView 低 8 点。

如果您一一检查日志中的碰撞约束，您会注意到您的两个约束 ConstraintHide 和 ConstraintShow 同时存在。

这是由您删除/添加约束引起的。

1. 初始状态

只有ConstraintHide 在视图中

1. 显示视图后的状态

ConstraintHide 正确删除，ConstraintShow 添加

1. 隐藏视图后的状态

ConstraintShow 未删除，ConstraintHide 添加

4. 碰撞

现在的问题是为什么第 3 步没有移除约束？这是因为第 2 步中的错误。您的 selectionCurrencyConstraintList 未正确更新，因此在第 3 步中您尝试删除原始的 ConstraintHide 约束，而不是第 2 步添加的约束 ConstraintShow。

这是因为if var constraints = selectionCurrencyConstraintList 复制了数组。所以最后你必须保存更改。

解决方案

添加

selectionCurrencyConstraintList = constraints

到块的末尾。

话虽如此，您可以通过在 Interface Builder 中添加所有约束来大幅简化代码，将 ConstraintShow 和 ConstraintHide 连接为插座，而不是删除/添加它们，只需从 0 更改它们的优先级到1000。