ios - 第二次加载UIView后，NSConstraints使应用程序崩溃

我有一个自定义的UIView，我使用此功能在视图控制器中实例化了该属性，displayTimer是视图控制器的iVar：

func changeViewModeTo(mode: String){

    if mode == "settings" {
        addSettingsModeConstraints()
        animatedLayoutIfNeeded(removeView: true)
    }
    if mode == "timer" {

        displayedTimer = TimerView.init()
        displayedTimer.frame = CGRect(x: (self.view.bounds.size.width)/2 - 50, y: (self.view.bounds.size.height)/2 - 80, width: 100, height: 160)

        let colors = timer.getColorScheme()
        displayedTimer.setColorScheme(colorLight: colors["lightColor"]!, colorDark: colors["darkColor"]!)
        displayedTimer.setTimeRemainingLabel(timer.duration)
        displayedTimer.setCountDownBarFromPercentage(1.0)
        displayedTimer.layer.zPosition = 100 //make sure the timer view sits on top of the settings panel
        displayedTimer.timerLabel.hidden = false
        displayedTimer.translatesAutoresizingMaskIntoConstraints = false

        let pinchGestureRecogniser = UIPinchGestureRecognizer(target: self, action: #selector(self.pinchDetected(_:)))

        displayedTimer.addGestureRecognizer(pinchGestureRecogniser)

        self.view.addSubview(displayedTimer)

        addTimerModeConstraints()
        animatedLayoutIfNeeded(removeView: false)

    }

}

如果将模式设置为计时器，则它将创建UIView的子类并为其设置实例变量，添加约束以使其全屏显示，然后调用动画layoutIfNeeded（）。如果正在设置的模式是设置，则它将禁用timerConstraints，添加新的约束以缩小视图，调用动画的layoutIfNeeded，然后将视图从superView中移除。

func animatedLayoutIfNeeded(removeView removeView: Bool){
    UIView.animateWithDuration(0.2, delay: 0, options: [UIViewAnimationOptions.CurveEaseIn] , animations: {
        self.view.layoutIfNeeded()
    }) { (true) in
        if removeView == true {
            self.displayedTimer.removeFromSuperview()
        }
    }
}

使用以下方法添加和删除约束（settingsConstraints和timerConstraints是视图控制器的iVars）：

//MARK: - Layout Constraints
func addSettingsModeConstraints() {

    let views = ["timerView": displayedTimer]

    let timerHorizontalConstraints = NSLayoutConstraint.constraintsWithVisualFormat(
        "H:|-75-[timerView]-75-|",
        options: [],
        metrics: nil,
        views: views)
    settingsConstraints += timerHorizontalConstraints

    let timerVerticalConstraints = NSLayoutConstraint.constraintsWithVisualFormat(
        "V:|-105-[timerView]-85-|",
        options: [],
        metrics: nil,
        views: views)
    settingsConstraints += timerVerticalConstraints

    NSLayoutConstraint.deactivateConstraints(timerConstraints)
    NSLayoutConstraint.activateConstraints(settingsConstraints)
}

func addTimerModeConstraints() {

    let views = ["timerView": displayedTimer]

    let timerHorizontalConstraints = NSLayoutConstraint.constraintsWithVisualFormat(
        "H:|-0-[timerView]-0-|",
        options: [],
        metrics: nil,
        views: views)
    timerConstraints += timerHorizontalConstraints

    let timerVerticalConstraints = NSLayoutConstraint.constraintsWithVisualFormat(
        "V:|-0-[timerView]-0-|",
        options: [],
        metrics: nil,
        views: views)
    timerConstraints += timerVerticalConstraints

    NSLayoutConstraint.activateConstraints(timerConstraints)
}

从捏手势识别器中调用changeViewModeTo（负捏设置一种模式，正捏设置另一种模式）。

我第一次捏合时，该视图已创建并进入全屏显示。然后，我反向捏合，视图缩小并被移除。然后，当我再次捏捏以通过应用程序崩溃启动该过程时，没有控制台错误，但代码行上出现红色错误：NSLayoutConstraint.activateConstraints(timerConstraints)



我猜想删除子视图已经导致对NSConstraints的引用消失了？

我无法弄清楚任何想法。

最佳答案

因此，事实证明这是一个简单的解决方法，在重新创建并激活它们之前，先对removeAll()和settingsConstraints调用timerConstraints即可解决问题。