constraint changes fail to animate -- SOLVED

[Eli Burke]

I've struggled for several hours now trying to figure out why my constraint changes weren't animating.

There is no issue with TinyConstraints (which is great, thanks Robert) just user error. But I thought it was worth a footnote in the README or an archived issue to hopefully save someone else the same hair pulling.

If you are following the suggested method of animating a set of constraints, and they immediately take effect without any lovely animation, make sure you are calling setNeedsLayout() on the superview containing the views you want to animate

    constraints1 = subview.edges(to: superview)
     constraints2 = subview.edges(to: superview, insets: UIEdgeInsets(top: 10, left: 10, bottom: 0, right: 0))
    ...
     constraints1.deActivate()
     constraints2.activate()
     UIViewPropertyAnimator(duration: 1, dampingRatio: 0.4) {
          //self.subview.layoutIfNeeded()   // WRONG-- won't animate
          self.view.layoutIfNeeded()        // RIGHT-- will animate
        }.startAnimation()