Question

以编程方式（没有情节提要），我尝试删除一组约束并在设备旋转时创建一组新约束。我用来删除约束的代码可以正确执行，但实际上并没有删除约束。添加新的（冲突的）约束集时，这会导致布局错误。

我正在使用没有故事板的Xcode 10.1和Swift 4.2。在我的MainViewController中，我正在根据viewDidLoad()调用的函数创建并放置一个名为“ ticketsView”的UICollectionView。在addChild()和addSubview()之后，我调用了一个名为applyTicketsViewConstraints()的函数，该函数确定设备的当前方向，然后（预期）删除所有现有约束并为它们应用适当的约束集当前的设备方向。

我重写viewWillTransition:toSize:withCoordinator()，只要旋转设备，它就会从协调器闭包内部调用相同的applyTicketsViewConstraints()函数。

在应用启动时，将根据初始设备方向正确应用约束。第一次将设备旋转90度时，显示也会成功更改，但是此后的任何旋转都会导致“ [LayoutConstraints]无法同时满足约束条件”错误消息。

我尝试遍历现有的ticketView约束并一次删除一个约束，并且尝试一次将其全部删除-但两种方法都无法真正去除约束。它们似乎都可以成功运行，但是约束完成后仍然存在。

    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，以便可以使用不同的值重新创建它们。我似乎找不到消除它们的方法（有效）。上面的代码在上面的两行中注释掉，表明我也尝试了它们（未成功）。

Answer 1

您可以尝试

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 } 
}

也可能是

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

Answer 2

我认为您必须使用激活/停用约束，例如：

为其创建变量，并在setupConstrainsMethod中设置约束值。 var notRotatedYConstraint：NSLayoutConstraint！

        var rotatedYConstraint: NSLayoutConstraint!

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

在您的功能中旋转iPhone的时间。 NSLayoutConstraint.deactivate（[notRotatedYConstraint]） NSLayoutConstraint.activate（[rotatedYConstraint]）

Answer 3

发布的前2个答案合起来可以为我提供所需的答案。 @Sh_Khan指示我使用NSLayoutConstraint数组。 @Wurzel指出，我应该使用NSLayoutConstraint.activate（）和.deactivate（）函数一次启用/禁用整个约束组。

因此，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，然后每次方向改变时，我在两个数组上调用deactivate函数，然后重新创建并激活适当的数组。

（safeAreaLayoutGuide会在设备方向发生变化时发生变化，这就是为什么我无法预先预先创建两组约束的原因。我还想要一种在约束变得更加动态的情况下也可以使用的解决方案，例如响应给用户调整显示区域的大小）

我的原始代码现在变为：

    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()
    }
}

我该如何解决UICollectionView的“ removeConstraint（）不起作用”问题？

3 个答案: