快速更新约束

我将约束添加到我的创建的按钮中UIView

func CreateButtonWithIndex(index:Int) {

    newButton.setTranslatesAutoresizingMaskIntoConstraints(false)

    self.view.addSubview(newButton)

    let newButtonConstraintL = NSLayoutConstraint(item: newButton, attribute: .Height, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 1.0, constant: 50)
    let newButtonConstraintH = NSLayoutConstraint(item: newButton, attribute: .Width, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 1.0, constant: 50)
    var newButtonConstraintX = NSLayoutConstraint(item: newButton, attribute: .CenterX, relatedBy: .Equal, toItem: view, attribute: .CenterX, multiplier: 1, constant: CGFloat(riga))
    var newButtonConstraintY = NSLayoutConstraint(item: newButton, attribute: .CenterY, relatedBy: .Equal, toItem: view, attribute: .CenterY, multiplier: 1, constant: CGFloat(colonna))

    view.addConstraints([newButtonConstraintX,newButtonConstraintY,newButtonConstraintH,newButtonConstraintL])

    var pan = UIPanGestureRecognizer(target:self, action:"pan:")
    pan.maximumNumberOfTouches = 2
    pan.minimumNumberOfTouches = 1
    newButton.addGestureRecognizer(pan)
}

func pan(rec:UIPanGestureRecognizer) {
  case .Ended: 
        if let subview = selectedView {
            if let button = rec.view as? UIButton {
                if let title = button.titleForState(.Normal){
                    button.setTranslatesAutoresizingMaskIntoConstraints(false)
                    let line = Float(p.x % snapX)
                    let column = Float(p.x % snapY)
                    let constraintL = NSLayoutConstraint(item: button, attribute: .Height, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 1.0, constant: 50)
                    let constraintH = NSLayoutConstraint(item: button, attribute: .Width, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 1.0, constant: 50)
                    var constraint2 = NSLayoutConstraint(item: button, attribute: .CenterX, relatedBy: .Equal, toItem: view, attribute: .CenterX, multiplier: 1, constant: CGFloat(line))
                    var constraint3 = NSLayoutConstraint(item: button, attribute: .CenterY, relatedBy: .Equal, toItem: view, attribute: .CenterY, multiplier: 1, constant: CGFloat(column))

                    view.addConstraints([constraint2,constraint3,constraintL.constraintH])
                }
            }
        }
}

在我的项目中，我的用户可以移动这些按钮，然后我尝试向识别的按钮添加更多约束，但我只是得到无尽的错误约束

  "<NSLayoutConstraint:0x7f8e5a4e9450 UIButton:0x7f8e5a644f60'Button6'.centerX == UIView:0x7f8e5a648bc0.centerX - 120>",
  "<NSLayoutConstraint:0x7f8e5a5be040 'UIView-Encapsulated-Layout-Width' H:[UIView:0x7f8e5a648bc0(736)]>",
  "<NSAutoresizingMaskLayoutConstraint:0x7f8e5a5be1f0 h=-&- v=-&- 'UIView-Encapsulated-Layout-Left' H:|-(0)-[UIView:0x7f8e5a648bc0]   (Names: '|':UITransitionView:0x7f8e5a5a8190 )>",
  "<NSAutoresizingMaskLayoutConstraint:0x7f8e5a5b53b0 h=--& v=--& UIButton:0x7f8e5a644f60'Button6'.midX == + 200>"

将尝试通过打破约束来恢复

"<NSLayoutConstraint:0x7f8e5a4e9450 UIButton:0x7f8e5a644f60'Button6'.centerX == UIView:0x7f8e5a648bc0.centerX - 120>"

"<NSLayoutConstraint:0x7f8e5a4e9510 UIButton:0x7f8e5a644f60'Button6'.centerY == UIView:0x7f8e5a648bc0.centerY - 40>",
"<NSLayoutConstraint:0x7f8e5a5be1a0 'UIView-Encapsulated-Layout-Height' V:[UIView:0x7f8e5a648bc0(414)]>",
"<NSAutoresizingMaskLayoutConstraint:0x7f8e5a5be240 h=-&- v=-&- 'UIView-Encapsulated-Layout-Top' V:|-(0)-[UIView:0x7f8e5a648bc0]   (Names: '|':UITransitionView:0x7f8e5a5a8190 )>",
"<NSAutoresizingMaskLayoutConstraint:0x7f8e5a5b82d0 h=--& v=--& UIButton:0x7f8e5a644f60'Button6'.midY == + 189>"

将尝试通过打破约束来恢复

<NSLayoutConstraint:0x7f8e5a4e9510 UIButton:0x7f8e5a644f60'Button6'.centerY == UIView:0x7f8e5a648bc0.centerY - 40>

...我应该更新 newButtonConstraintX / Y 但我不明白如何做到这一点？

问题是您添加的新约束与现有约束冲突。

您有几个选择：

1. 从 iOS 8 开始，您可以设置active财产给false在添加新约束之前先检查约束。

2. 在 8 之前的 iOS 版本中，您需要在添加新约束之前删除旧约束。

3. 理想情况下，最好不必激活/停用（或者更糟糕的是添加和删除）约束，而只需修改constant单一约束的性质。例如在 Swift 3/4 中：

   class ViewController: UIViewController {
   
       private var xConstraint: NSLayoutConstraint!
       private var yConstraint: NSLayoutConstraint!
   
       override func viewDidLoad() {
           super.viewDidLoad()
   
           let label = UILabel()
           label.text = "x"
           label.translatesAutoresizingMaskIntoConstraints = false
           view.addSubview(label)
   
           // I don't really need to save references to these, so these are local variables
   
           let widthConstraint = label.widthAnchor.constraint(equalToConstant: 50)
           let heightConstraint = label.heightAnchor.constraint(equalToConstant: 50)
   
           // but since I'll be modifying these later, these are class properties
   
           xConstraint = label.centerXAnchor.constraint(equalTo: view.centerXAnchor)
           yConstraint = label.centerYAnchor.constraint(equalTo: view.centerYAnchor)
   
           NSLayoutConstraint.activate([widthConstraint, heightConstraint, xConstraint, yConstraint])
   
           let pan = UIPanGestureRecognizer(target: self, action: #selector(handlePan(_:)))
           view.addGestureRecognizer(pan)
       }
   
       private var originalCenter: CGPoint!
   
       @objc func handlePan(_ gesture: UIPanGestureRecognizer) {
           if gesture.state == .began {
               originalCenter = CGPoint(x: xConstraint.constant, y: yConstraint.constant)
           }
   
           let translation = gesture.translation(in: gesture.view!)
   
           xConstraint.constant = originalCenter.x + translation.x
           yConstraint.constant = originalCenter.y + translation.y
       }
   
   }
   

   当修改可以达到想要的效果时constant的约束，这通常是最好的。

对于 Swift 2 语法，请参阅此答案的先前修订版.