Animating constraints with layer-backed NSView - animation

Question

I'm attempting to implement an animation that shows/hides a view in a horizontal arrangement. I'd like this to happen with slide, and with no opacity changes. I'm using auto-layout everywhere.
Critically, the total width of the containing view changes with the window. So, constant-based animations are not possible (or so I believe, but happy to be proved wrong).
|- viewA -|- viewB -|
My first attempt was to use NSStackView, and animate the isHidden property of an arranged subview. Despite seeming like it might do the trick, I was not able to pull off anything close to what I was after.
My second attempt was to apply two constraints, one to force viewB to be zero width, and a second to ensure the widths are equal. On animation I change the priorities of these constraints from defaultHigh <-> defaultLow.
This results in the correct layout in both cases, but the animation is not working out.
With wantsLayer = true on the containing view, no animation occurs whatsoever. The views just jump to their final states. Without wantsLayer, the views do animate. However, when collapsing, viewA does a nice slide, but viewB instantly disappears. As an experiment, I changed the zero width to a fixed 10.0, and with that, the animation works right in both directions. However, I want the view totally hidden.
So, a few questions:
Is it possible to animate layouts like this with layer-backed views?
Are there other techniques possible for achieving the same effect?
Any ideas on how to achieve these nicely with NSStackView?
class LayoutAnimationViewController: NSViewController {
let containerView: NSView
let view1: ColorView
let view2: ColorView
let widthEqualContraint: NSLayoutConstraint
let widthZeroConstraint: NSLayoutConstraint
init() {
self.containerView = NSView()
self.view1 = ColorView(color: NSColor.red)
self.view2 = ColorView(color: NSColor.blue)
self.widthEqualContraint = view2.widthAnchor.constraint(equalTo: view1.widthAnchor)
widthEqualContraint.priority = .defaultLow
self.widthZeroConstraint = view2.widthAnchor.constraint(equalToConstant: 0.0)
widthZeroConstraint.priority = .defaultHigh
super.init(nibName: nil, bundle: nil)
}
required init?(coder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
override func loadView() {
self.view = containerView
// view.wantsLayer = true
view.addSubview(view1)
view.addSubview(view2)
view.subviewsUseAutoLayout = true
NSLayoutConstraint.activate([
view1.topAnchor.constraint(equalTo: view.topAnchor),
view1.bottomAnchor.constraint(equalTo: view.bottomAnchor),
view1.leadingAnchor.constraint(equalTo: view.leadingAnchor),
// view1.trailingAnchor.constraint(equalTo: view2.leadingAnchor),
view2.topAnchor.constraint(equalTo: view.topAnchor),
view2.bottomAnchor.constraint(equalTo: view.bottomAnchor),
view2.leadingAnchor.constraint(equalTo: view1.trailingAnchor),
view2.trailingAnchor.constraint(equalTo: view.trailingAnchor),
widthEqualContraint,
widthZeroConstraint,
])
}
func runAnimation() {
view.layoutSubtreeIfNeeded()
self.widthEqualContraint.toggleDefaultPriority()
self.widthZeroConstraint.toggleDefaultPriority()
// self.leadingConstraint.toggleDefaultPriority()
NSAnimationContext.runAnimationGroup({ (context) in
context.allowsImplicitAnimation = true
context.duration = 3.0
self.view.layoutSubtreeIfNeeded()
}) {
Swift.print("animation complete")
}
}
}
extension LayoutAnimationViewController {
#IBAction func runTest1(_ sender: Any?) {
self.runAnimation()
}
}
Also, some potentially relevant, but so far unhelpful, related questions:
Animating Auto Layout changes concurrently with NSPopover contentSize change
Animating Auto Layout constraints with NSView.layoutSubtreeIfNeeded() not working on macOS High Sierra
Hide view item of NSStackView with animation