Set back to original uilayoutconstraint - zoom in animation - ios

Question

Using a Storyboard, I have a height constraint with 2 size class (one for regular at 200pt, one for compact at 100pt).
Because I'm animating it when the view appears, the height of the element goes from 0 (initial state) -> 200pt for regular or 100pt for compact (final state).
It is a simple "zoomIn" animation.
But the thing is that because I change programmatically the constant, I'm losing the class sizes meaning when I rotate the phone, I have to set the constant to the right size instead of having Interface Builder's automatic class size.
So how would you apply an animation to an UIElement with auto-layout (and without having to create spaghetti code in viewWillLayoutSubviews, viewDidLayoutSubviews)?

Answer 1

Without your code, it's not clear exactly what you're doing, but here goes anyway :) First, the best way to animate when you are using autolayout is to animate the constraint changes, e.g.:
myConstraint.constant = myConstraintInitialConstant
UIView.animateWithDuration(animationSpeed) {
self.view.layoutIfNeeded()
}
The most important thing to note here is that the constraint change is outside the animation block, what you animate is layoutIfNeeded().
But you want to know what your initial constant was when the nib was loaded, yes? Then save it in viewDidLoad(), e.g.:
private var myConstraintInitialConstant: CGFloat = 65
override func viewDidLoad() {
super.viewDidLoad()
myConstraintInitialConstant = myConstraint.constant
}

Answer 2

Did you try to play with the layoutIfNeeded() / layoutSubviews() methods ? This will update the frame of your UIElement after added new constraints to it
I had a top constraint set to 0 and I animate it like that :
override func layoutSubviews() {
super.layoutSubviews()
// I reset my constraint's constant if already animate
if(topConst.constant > 0){
topConst.constant = 0
}
self.viewToAnimate.layoutIfNeeded()
//Animate the constraint
topConst.constant = 100
UIView.animateWithDuration(0.8, delay: 0.2, usingSpringWithDamping: 0.7, initialSpringVelocity: 0, options: .CurveEaseIn, animations: { () -> Void in
self.viewToAnimate.layoutIfNeeded()
}, completion: nil)
}
I used layoutSubviews it works fine :D