自动布局将尝试通过打破约束来恢复

Question

我想在其 superView 的右上角布置一个标签，尾部 8pt，底部 10pt

这是我的代码：

  let label = UILabel(frame: CGRectZero)
  label.text = "text goes here"
  label.textColor = UIColor.whiteColor()
  label.translatesAutoresizingMaskIntoConstraints = false
  label.numberOfLines = 0
  label.textAlignment = .Right
  label.backgroundColor = UIColor.blackColor()
  label.font = UIFont(name: "TheSans-Plain", size: 17)
  imageTitleContainer.addSubview(label)


    let label_constraint_H:Array = NSLayoutConstraint.constraintsWithVisualFormat("H:|-(>=8)-[label]-(8)-|", options: NSLayoutFormatOptions(rawValue: 0), metrics: nil, views: ["label":label])

    let label_constraint_V:Array = NSLayoutConstraint.constraintsWithVisualFormat("V:[label]-(10)-|", options: NSLayoutFormatOptions(rawValue: 0), metrics: nil, views: ["label":label])

    imageTitleContainer.addConstraints(label_constraint_H)
    imageTitleContainer.addConstraints(label_constraint_V)`

但我在 console

中得到 Unable to simultaneously satisfy constraints

Will attempt to recover by breaking constraint <NSLayoutConstraint:0x7ff55acf24c0 H:[UILabel:0x7ff55acf1af0'text goes here']-(8)-| (Names: '|':UIView:0x7ff55acbf430 )>

注意：0x7ff55acbf430是我在代码中的imageTitleContainer

更新：其他约束： "<NSLayoutConstraint:0x7ff55accdc80 H:|-(0)-[UIView:0x7ff55acbf430] (Names: '|':UIView:0x7ff55acca080 )>", "<NSLayoutConstraint:0x7ff55accdcd0 H:[UIView:0x7ff55acbf430]-(0)-| (Names: '|':UIView:0x7ff55acca080 )>", "<NSLayoutConstraint:0x7ff55acf2450 H:|-(>=8)-[UILabel:0x7ff55acf1af0'text goes here'] (Names: '|':UIView:0x7ff55acbf430 )>", "<NSLayoutConstraint:0x7ff55acf24c0 H:[UILabel:0x7ff55acf1af0'text goes here']-(8)-| (Names: '|':UIView:0x7ff55acbf430 )>", "<NSLayoutConstraint:0x7ff55adb3830 'UIView-Encapsulated-Layout-Width' H:[UIView:0x7ff55acca080(0)]>" )

Answer 1

尝试降低其中一项约束的优先级，例如

H:|-(>=8@999)-[label]-(8)-|

必须这样做才能让 UICollectionView 进行布局工作。请注意名为 UIView-Encapsulated-Layout-Width 的零宽度约束会破坏您的布局。

自动布局将尝试通过打破约束来恢复

Autolayout Will attempt to recover by breaking constraint

ios

autolayout

nslayoutconstraint

visual-format-language