NSConstraints crashes app after second load of UIView - ios

Question

I've got a custom UIView that I instantiate in a view controller with this function, displayedTimer is an iVar of the view controller:
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)
}
}
If the mode is set to timer then it creates a subclass of UIView and sets an instance variable to it, constraints are added to make it full screen and then an animated layoutIfNeeded() is called. If the mode being set is settings then it deactivates the timerConstraints, adds new constraints to shrink the view, calls an animated layoutIfNeeded and then removes the view from the superView.
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()
}
}
}
The constraints are added and removed with these methods (settingsConstraints and timerConstraints are iVars of the view controller):
//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 is called from a pinch gesture recogniser (negative pinch sets one mode, positive pinch sets another mode).
The first time I pinch, the view is created and goes full screen. I then reverse pinch and the view shrinks and is removed. Then when I pinch again to start the process over the app crashes, there are no console errors but there is a red error over the line of code: NSLayoutConstraint.activateConstraints(timerConstraints)
I'm guessing removing the subview has caused the reference to NSConstraints to disappear?
Any thoughts would be great as I can't figure it out.

Answer 1

So turns out this is a simple fix, call removeAll() on settingsConstraints and timerConstraints before recreating them and activating them solves the problem.