Question

我有一个用户可以花费和收缩的结果容器。我想删除一个约束并添加一个新约束。单击它可以正常工作但第二次单击（即设置newConstraint.active = false并且resultTopConstraint = true会导致崩溃）。我有以下内容：

  @IBAction func toggleResultContainer(sender: AnyObject) {

    isResultsOpen = !isResultsOpen

    //resultTopConstraint.constant =  isResultsOpen ? -300.0 : 0.0

    self.view.sendSubviewToBack(searchView)

    let newConstraint = NSLayoutConstraint(
      item: resultsContainer,
      attribute: .Top,
      relatedBy: .Equal,
      toItem: resultsContainer.superview!,
      attribute: .Top,
      multiplier: 1.0,
      constant: 30.0
    )

    if(isResultsOpen){
      resultTopConstraint.active = false
      newConstraint.active = true
    }else{
      resultTopConstraint.active = true
      newConstraint.active = false
    }

    UIView.animateWithDuration(1.0, delay: 0.0, usingSpringWithDamping: 0.4, initialSpringVelocity: 10.0, options: .CurveEaseIn, animations: {
        self.view.layoutIfNeeded()
      }, completion: nil)

并获取Unable to simultaneously satisfy constraints.

上述代码是否有效，这是否同时满足约束问题？我试过设置约束

  @IBOutlet var resultTopConstraint: NSLayoutConstraint!

同时weak和strong（每https://stackoverflow.com/a/28717185/152825）但似乎没有效果。甲

Answer 1

试试这个：

if (isResultsOpen) {
      NSLayoutConstraint.deactivateConstraints([resultTopConstraint])
      NSLayoutConstraint.activateConstraints([newConstraint])
    } else {
      NSLayoutConstraint.deactivateConstraints([newConstraint])
      NSLayoutConstraint.activateConstraints([resultTopConstraint])
    }

可以重新激活NSLayoutConstraint吗？

1 个答案: