Swift 更新约束

Swift Update Constraint(Swift 更新约束)

问题描述

我将约束添加到在我的 UIView

I added the constraint to the buttons created in my 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，然后我尝试为识别的按钮添加更多约束，但我得到了一个无穷无尽的错误约束

In My Project my users can move these buttons and then I tried to add more constraints to the buttons recognized but I just get an endless error constraint

  "<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

Will attempt to recover by breaking constraint

"<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

Will attempt to recover by breaking constraint

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

...我应该更新 newButtonConstraintX/Y 但我不明白我该怎么做吗?

... should I update newButtonConstraintX / Y but I'm not understanding how I can do this ?

推荐答案

问题是您正在添加一个与现有约束冲突的新约束.

The issue is that you're adding a new constraint that conflicts with the existing constraint.

你有几个选择:

1. 在 iOS 8 中生效，您可以在添加新约束之前将约束的 active 属性设置为 false.

在 iOS 8 之前的版本中，您可能希望在添加新约束之前删除旧约束.

In iOS versions prior to 8, you would want to remove the old constraints before adding new constraints.

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，而只需修改单个约束的 constant 属性.例如在 Swift 3/4 中:

Ideally, it's best to not have to activate/deactivate (or, worse, add and remove) constraints, but rather just modify the constant property of a single constraint. For example in Swift 3/4:

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
    }

}

当通过修改约束的constant可以达到想要的效果时，一般是最好的.

When the desired effect can be achieved by modifying the constant of the constraint, that's generally best.

有关 Swift 2 语法，请参阅此答案的上一版本.

For Swift 2 syntax, see previous revision of this answer.

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