如何解决我的 UICollectionView 的“removeConstraint() not working”问题？

Question

以编程方式（没有情节提要），我试图删除一组约束并在设备旋转时创建一个新集。我用来删除约束的代码执行没有错误，但实际上并没有删除约束。这会在添加新的（冲突的）约束集时导致布局错误。

我正在使用没有情节提要的 Xcode 10.1 和 Swift 4.2。在我的 MainViewController 中，我从viewDidLoad() 调用的函数中创建并放置了一个名为“ticketsView”的 UICollectionView。在addChild() 和addSubview() 之后，我调用了一个名为applyTicketsViewConstraints() 的函数，它确定设备的当前方向，然后（预计）删除任何现有约束并为当前设备方向应用适当的一组约束。

每当设备旋转时，我都会覆盖 viewWillTransition:toSize:withCoordinator()，它会从协调器闭包中调用相同的 applyTicketsViewConstraints() 函数。

在应用启动时，会根据初始设备方向正确应用约束。设备第一次旋转 90 度时，显示也成功更改，但之后的任何旋转都会导致“[LayoutConstraints] 无法同时满足约束”错误消息。

我尝试循环遍历现有的 ticketView 约束并一次删除它们，并且我尝试一次将它们全部删除 - 但两种方法都不会导致实际删除约束。它们似乎都运行成功，但完成后约束仍然存在。

    func createTicketCollectionWindow() {
        ticketsLayout = UICollectionViewFlowLayout()
        ticketsVC = TicketCollectionController(collectionViewLayout: ticketsLayout)
        ticketsVC?.collectionView?.backgroundColor = UIColor.darkGray
        ticketsView = ticketsVC!.view
        ticketsView.translatesAutoresizingMaskIntoConstraints = false
        addChild(ticketsVC!)
        self.view.addSubview(ticketsView)
        applyTicketsViewConstraints()
    }

    func applyTicketsViewConstraints() {
        let safe = self.view.safeAreaLayoutGuide
        let deviceSize = UIScreen.main.bounds.size
        for individualConstraint in ticketsView.constraints {
            print("TicketViewConstraints:   Removing Constraint: \(individualConstraint)" )
            // ticketsView.removeConstraint(individualConstraint)
        }
        ticketsView.removeConstraints(ticketsView.constraints)
        // self.view.removeConstraints(ticketsView.constraints)
        if deviceSize.width < deviceSize.height {
            print("TicketsView Constraint:  Device is in PORTRAIT orientation!")
            ticketsView.leadingAnchor.constraint(equalTo: safe.trailingAnchor, constant: -safe.layoutFrame.width).isActive = true
            ticketsView.trailingAnchor.constraint(equalTo:safe.trailingAnchor, constant: 0 ).isActive = true
            ticketsView.bottomAnchor.constraint(equalTo: safe.bottomAnchor, constant: 0).isActive = true
            ticketsView.heightAnchor.constraint(equalToConstant: safe.layoutFrame.height * 0.75).isActive = true
        } else {
            print("TicketsView Constraint:  Device is in LANDSCAPE orientation!")
            ticketsView.leadingAnchor.constraint(equalTo: safe.trailingAnchor, constant: -safe.layoutFrame.width).isActive = true
            ticketsView.trailingAnchor.constraint(equalTo:safe.trailingAnchor, constant: 0 ).isActive = true
            ticketsView.bottomAnchor.constraint(equalTo: safe.bottomAnchor, constant: 0).isActive = true
            ticketsView.heightAnchor.constraint(equalToConstant: safe.layoutFrame.height * 0.65).isActive = true
        }
        ticketsView.layoutIfNeeded()
    }

    override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {
        super.viewWillTransition(to: size, with: coordinator)
        coordinator.animate(alongsideTransition: { (_) in
            self.applyTicketsViewConstraints()
            self.ticketsVC?.collectionView.reloadData()
        }) { (_) in
            self.ticketsView.layoutIfNeeded()
        }
    }

我希望我在上面的代码中创建的 4 个约束将被删除，以便我可以使用不同的值重新创建它们。我似乎找不到删除它们的方法（有效）。上面代码中注释掉的上面两行表明我也尝试过（不成功）。

Answer 1

你可以试试

var portrait = [NSLayoutConstraint]()
var landscape = [NSLayoutConstraint]()

let porCon1  = ticketsView.leadingAnchor.constraint(equalTo: safe.trailingAnchor, constant: -safe.layoutFrame.width) 
let porCon2  =  ticketsView.trailingAnchor.constraint(equalTo:safe.trailingAnchor, constant: 0 ) 
let porCon3  = ticketsView.bottomAnchor.constraint(equalTo: safe.bottomAnchor, constant: 0) 
let porCon4  = ticketsView.heightAnchor.constraint(equalToConstant: safe.layoutFrame.height * 0.75) 

portrait = [porCon1,porCon2,porCon3,porCon4]

let landCon1  = ticketsView.leadingAnchor.constraint(equalTo: safe.trailingAnchor, constant: -safe.layoutFrame.width) 
let landCon1  = ticketsView.trailingAnchor.constraint(equalTo:safe.trailingAnchor, constant: 0 ) 
let landCon1  = ticketsView.bottomAnchor.constraint(equalTo: safe.bottomAnchor, constant: 0) 
let landCon1  = ticketsView.heightAnchor.constraint(equalToConstant: safe.layoutFrame.height * 0.65) 

landscape = [landCon1,landCon2,landCo3,landCon4]

---

func setPortrait(_ por:Bool) {  
    portrait.forEach { $0.isActive = por }
    landscape.forEach { $0.isActive = !por } 
}

---

也可以

NSLayoutConstraint.deActivate(portrait)
NSLayoutConstraint.deActivate(landscape)
if por {
   NSLayoutConstraint.activate(portrait)
}
else { 
  NSLayoutConstraint.activate(landscape)
}

Answer 2

我相信您必须使用激活/停用约束，例如：

为它们创建变量并在 setupConstrainsMethod 中设置约束值。 var notRotatedYConstraint: NSLayoutConstraint！

        var rotatedYConstraint: NSLayoutConstraint!

在 viewdidload 中： NSLayoutConstraint.activate([notRotatedYConstraint])

在 iPhone 旋转时的函数中。 NSLayoutConstraint.deactivate([notRotatedYConstraint]) NSLayoutConstraint.activate([rotatedYConstraint])

Answer 3

发布的前 2 个答案结合在一起，为我提供了所需的答案。 @Sh_Khan 指示我使用 NSLayoutConstraint 数组。 @Wurzel 指出我应该使用 NSLayoutConstraint.activate() 和 .deactivate() 函数一次性启用/禁用整个约束组。

所以，关键是将所有纵向约束添加到一个数组，将所有横向约束添加到另一个数组，然后每次方向更改时，我都会在两个数组上调用 deactivate 函数，然后重新创建和激活相应的数组。

（当设备方向发生变化时，safeAreaLayoutGuide 会发生变化，这就是为什么我无法提前预先创建两组约束。我还想要一个解决方案，如果约束变得更加动态 - 例如响应给用户调整显示区域的大小）

我原来的代码现在变成了：

    func applyTicketsViewConstraints() {
        let safe = self.view.safeAreaLayoutGuide
        let deviceSize = UIScreen.main.bounds.size

        NSLayoutConstraint.deactivate(portraitTicketsViewConstraints)
        NSLayoutConstraint.deactivate(landscapeTicketsViewConstraints)

        if deviceSize.width < deviceSize.height {
            print("TicketsView Constraint:  Device Size is in PORTRAIT orientation!")
            portraitTicketsViewConstraints = [
                ticketsView.leadingAnchor.constraint(equalTo: safe.trailingAnchor, constant: -safe.layoutFrame.width),
                ticketsView.trailingAnchor.constraint(equalTo: safe.trailingAnchor, constant: 0 ),
                ticketsView.bottomAnchor.constraint(equalTo: safe.bottomAnchor, constant: 0),
                ticketsView.heightAnchor.constraint(equalToConstant: safe.layoutFrame.height * 0.75)
            ]
            NSLayoutConstraint.activate(portraitTicketsViewConstraints)
        } else {
            print("TicketsView Constraint:  Device Size is in LANDSCAPE orientation!")
            landscapeTicketsViewConstraints = [
                ticketsView.leadingAnchor.constraint(equalTo: safe.trailingAnchor, constant: -safe.layoutFrame.width),
                ticketsView.trailingAnchor.constraint(equalTo: safe.trailingAnchor, constant: 0 ),
                ticketsView.bottomAnchor.constraint(equalTo: safe.bottomAnchor, constant: 0),
                ticketsView.heightAnchor.constraint(equalToConstant: safe.layoutFrame.height * 0.65)
            ]
            NSLayoutConstraint.activate(landscapeTicketsViewConstraints)
        }
        ticketsView.layoutIfNeeded()
    }
}