斯威夫特更新约束 [英] Swift Update Constraint

问题描述

我添加了约束创建的按钮我的的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])
                }
            }
        }
}

在我的项目我的用户可以移动这些按钮，然后我尝试更多的约束添加到已识别的按钮，但我刚刚得到一个无尽的错误限制

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>"

将试图通过打破约束，以恢复

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>"

将试图通过打破约束，以恢复

Will attempt to recover by breaking constraint

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

...我应该更新newButtonConstraintX / Y，但我不明白我怎么能这样做呢？

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

推荐答案

的问题是，您要添加与现有的约束冲突的新的约束。

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

您有几种选择：

1. 在iOS的8起，您可以设置有效属性假您之前约束添加一个新的约束。

1. Effective in iOS 8, you can set the active property to false for a constraint before you add a new constraint.

在IOS版本之前的8，你想添加新的限制之前，删除旧的约束。

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

在理想情况下，最好不要有激活/关闭（或者更糟，添加和删除）的限制，而只是修改一个的恒属性一个约束。例如：

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:

class ViewController: UIViewController {

    private var xConstraint: NSLayoutConstraint!
    private var yConstraint: NSLayoutConstraint!

    override func viewDidLoad() {
        super.viewDidLoad()

        let label = UILabel()
        label.text = "x"
        label.setTranslatesAutoresizingMaskIntoConstraints(false)
        view.addSubview(label)

        // I don't really need to save references to these, so these are local variables

        let widthConstraint = NSLayoutConstraint(item: label, attribute: .Width, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 1.0, constant: 50)
        let heightConstraint = NSLayoutConstraint(item: label, attribute: .Height, relatedBy: .Equal, toItem: nil, attribute: .NotAnAttribute, multiplier: 1.0, constant: 50)

        // but since I'll be modifying these later, these are class properties

        xConstraint = NSLayoutConstraint(item: label, attribute: .CenterX, relatedBy: .Equal, toItem: view, attribute: .CenterX, multiplier: 1.0, constant: 0)
        yConstraint = NSLayoutConstraint(item: label, attribute: .CenterY, relatedBy: .Equal, toItem: view, attribute: .CenterY, multiplier: 1.0, constant: 0)

        view.addConstraints([widthConstraint, heightConstraint, xConstraint, yConstraint])

        let pan = UIPanGestureRecognizer(target: self, action: "handlePan:")
        view.addGestureRecognizer(pan)
    }

    private var originalCenter: CGPoint!

    func handlePan(gesture: UIPanGestureRecognizer) {
        if gesture.state == .Began {
            originalCenter = CGPoint(x: xConstraint.constant, y: yConstraint.constant)
        }

        let translation = gesture.translationInView(gesture.view!)

        xConstraint.constant = originalCenter.x + translation.x
        yConstraint.constant = originalCenter.y + translation.y
        view.setNeedsLayout()
    }

}

在理想的效果可以通过修改可以实现恒的约束，这是一般最好的。

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

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