Why my constraints isn't working as they should?

Question

I have some constraints in the Interface Builder so when the view loads I'm removing all the constraints and adding new ones from code but they are messed up

here is my code(I know it's a bad styled code with flags etc, sorry for it, but the question is why it making the layout wrong):

 override func viewWillAppear(animated: Bool) {

    super.viewWillAppear(true)

    self.view.layoutIfNeeded()
    self.view.setNeedsUpdateConstraints()
    self.view.layoutIfNeeded()
            self.buttonsArray.forEach() { button in
                NSLayoutConstraint(item: button, attribute: .CenterX, relatedBy: .Equal, toItem: self.view, attribute: .CenterX, multiplier: 1, constant: 0).active = true

                NSLayoutConstraint(item: button, attribute: .CenterY, relatedBy: .Equal, toItem: self.view, attribute: .CenterY, multiplier: 1, constant: 0).active = true

                NSLayoutConstraint(item: button, attribute: .Height, relatedBy: .Equal, toItem: self.view, attribute: .Height, multiplier: 0.15, constant: 0).active = true
            }
}

var flagForOriginalConstraints = 0
override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()

    if flagForOriginalConstraints == 0 {
    self.constraintsArray = self.view.constraints
    self.flagForOriginalConstraints += 1
        return
    }
    if flagForOriginalConstraints == 1 {
        self.view.removeConstraints()
        self.flagForOriginalConstraints += 1
         return
    } 
}

Answer 1

remove the return here

if flagForOriginalConstraints == 0 {
    self.constraintsArray = self.view.constraints
    self.flagForOriginalConstraints += 1
        return
    }

seems like first time you are just incrementing flagForOriginalConstraints count and then the function returns