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

Question

我有一个自定义 UIView，我使用此函数在 View Controller 中实例化它，displayTimer 是 View Controller 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)

    }

}

如果模式设置为计时器，那么它会创建 UIView 的子类并为其设置实例变量，添加约束以使其全屏，然后调用动画的layoutIfNeeded()。如果设置的模式是settings，那么它会停用timerConstraints，添加新的约束来缩小 View ，调用动画layoutIfNeeded，然后从superView中删除 View 。

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()
        }
    }
}

使用这些方法添加和删除约束(settingsConstraints和timerConstraints是 View Controller 的iVar):

//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)
}

changeViewModeTo 从捏合手势识别器调用(负捏合设置一种模式，正捏合设置另一种模式)。

我第一次捏合时， View 就会创建并全屏显示。然后我反向捏合， View 就会缩小并被删除。然后，当我再次捏捏以启动应用程序崩溃的过程时，没有控制台错误，但代码行上有红色错误: NSLayoutConstraint.activateConstraints(timerConstraints)

我猜测删除 subview 会导致对 NSConstraints 的引用消失？

任何想法都会很棒，因为我无法弄清楚。

Answer 1

事实证明这是一个简单的修复，在重新创建和激活它们之前对 settingsConstraints 和 timerConstraints 调用 removeAll() 即可解决问题.