How to expand and collapse NSSplitView subviews with animation?

Question

Is it possible to animate the collapsing and expanding of NSSplitView subviews? (I am aware of the availability of alternative classes, but would prefer using NSSplitView ov

Answer 1

Solution for macOS 10.11.

Main points:

1. NSSplitViewItem.minimumThickness depends of NSSplitViewItem .viewController.view width/height, if not set explicitly.

2. NSSplitViewItem .viewController.view width/height depends of explicitly added constraints.

3. NSSplitViewItem (i.e. arranged subview of NSSplitView) can be fully collapsed, if it can reach Zero dimension (width or height).

So, we just need to deactivate appropriate constrains before animation and allow view to reach Zero dimension. After animation we just need to activate needed constraints.

class SplitViewAnimationsController: ViewController {

   private lazy var toolbarView = StackView().autolayoutView()
   private lazy var revealLeftViewButton = Button(title: "Left").autolayoutView()
   private lazy var changeSplitOrientationButton = Button(title: "Swap").autolayoutView()
   private lazy var revealRightViewButton = Button(title: "Right").autolayoutView()

   private lazy var splitViewController = SplitViewController()

   private lazy var viewControllerLeft = ContentViewController()
   private lazy var viewControllerRight = ContentViewController()
   private lazy var splitViewItemLeft = NSSplitViewItem(viewController: viewControllerLeft)
   private lazy var splitViewItemRight = NSSplitViewItem(viewController: viewControllerRight)

   private lazy var viewLeftWidth = viewControllerLeft.view.widthAnchor.constraint(greaterThanOrEqualToConstant: 100)
   private lazy var viewRightWidth = viewControllerRight.view.widthAnchor.constraint(greaterThanOrEqualToConstant: 100)
   private lazy var viewLeftHeight = viewControllerLeft.view.heightAnchor.constraint(greaterThanOrEqualToConstant: 40)
   private lazy var viewRightHeight = viewControllerRight.view.heightAnchor.constraint(greaterThanOrEqualToConstant: 40)
   private lazy var equalHeight = viewControllerLeft.view.heightAnchor.constraint(equalTo: viewControllerRight.view.heightAnchor, multiplier: 1)
   private lazy var equalWidth = viewControllerLeft.view.widthAnchor.constraint(equalTo: viewControllerRight.view.widthAnchor, multiplier: 1)

   override func loadView() {
      super.loadView()
      splitViewController.addSplitViewItem(splitViewItemLeft)
      splitViewController.addSplitViewItem(splitViewItemRight)
      contentView.addSubviews(toolbarView, splitViewController.view)
      addChildViewController(splitViewController)

      toolbarView.addArrangedSubviews(revealLeftViewButton, changeSplitOrientationButton, revealRightViewButton)
   }

   override func viewDidAppear() {
      super.viewDidAppear()
      splitViewController.contentView.setPosition(contentView.bounds.width * 0.5, ofDividerAt: 0)
   }

   override func setupDefaults() {
      setIsVertical(true)
   }

   override func setupHandlers() {
      revealLeftViewButton.setHandler { [weak self] in guard let this = self else { return }
         self?.revealOrCollapse(this.splitViewItemLeft)
      }
      revealRightViewButton.setHandler { [weak self] in guard let this = self else { return }
         self?.revealOrCollapse(this.splitViewItemRight)
      }
      changeSplitOrientationButton.setHandler { [weak self] in guard let this = self else { return }
         self?.setIsVertical(!this.splitViewController.contentView.isVertical)
      }
   }

   override func setupUI() {

      splitViewController.view.translatesAutoresizingMaskIntoConstraints = false
      splitViewController.contentView.dividerStyle = .thin
      splitViewController.contentView.setDividerThickness(2)
      splitViewController.contentView.setDividerColor(.green)

      viewControllerLeft.contentView.backgroundColor = .red
      viewControllerRight.contentView.backgroundColor = .blue
      viewControllerLeft.contentView.wantsLayer = true
      viewControllerRight.contentView.wantsLayer = true

      splitViewItemLeft.canCollapse = true
      splitViewItemRight.canCollapse = true

      toolbarView.distribution = .equalSpacing
   }

   override func setupLayout() {
      var constraints: [NSLayoutConstraint] = []

      constraints += LayoutConstraint.Pin.InSuperView.horizontally(toolbarView, splitViewController.view)
      constraints += [
         splitViewController.view.topAnchor.constraint(equalTo: contentView.topAnchor),
         toolbarView.topAnchor.constraint(equalTo: splitViewController.view.bottomAnchor),
         toolbarView.bottomAnchor.constraint(equalTo: contentView.bottomAnchor)
      ]

      constraints += [viewLeftWidth, viewLeftHeight, viewRightWidth, viewRightHeight]
      constraints += [toolbarView.heightAnchor.constraint(equalToConstant: 48)]

      NSLayoutConstraint.activate(constraints)
   }
}

extension SplitViewAnimationsController {

   private enum AnimationType: Int {
      case noAnimation, `default`, rightDone
   }

   private func setIsVertical(_ isVertical: Bool) {
      splitViewController.contentView.isVertical = isVertical
      equalHeight.isActive = isVertical
      equalWidth.isActive = !isVertical
   }

   private func revealOrCollapse(_ item: NSSplitViewItem) {

      let constraintToDeactivate: NSLayoutConstraint
      if splitViewController.splitView.isVertical {
         constraintToDeactivate = item.viewController == viewControllerLeft ? viewLeftWidth : viewRightWidth
      } else {
         constraintToDeactivate = item.viewController == viewControllerLeft ? viewLeftHeight : viewRightHeight
      }

      let animationType: AnimationType = .rightDone

      switch animationType {
      case .noAnimation:
         item.isCollapsed = !item.isCollapsed
      case .default:
         item.animator().isCollapsed = !item.isCollapsed
      case .rightDone:
         let isCollapsedAnimation = CABasicAnimation()
         let duration: TimeInterval = 3 // 0.15
         isCollapsedAnimation.duration = duration
         item.animations = [NSAnimatablePropertyKey("collapsed"): isCollapsedAnimation]
         constraintToDeactivate.isActive = false
         setActionsEnabled(false)
         NSAnimationContext.runImplicitAnimations(duration: duration, animations: {
            item.animator().isCollapsed = !item.isCollapsed
         }, completion: {
            constraintToDeactivate.isActive = true
            self.setActionsEnabled(true)
         })
      }
   }

   private func setActionsEnabled(_ isEnabled: Bool) {
      revealLeftViewButton.isEnabled = isEnabled
      revealRightViewButton.isEnabled = isEnabled
      changeSplitOrientationButton.isEnabled = isEnabled
   }
}

class ContentViewController: ViewController {

   override func viewDidLayout() {
      super.viewDidLayout()
      print("frame: \(view.frame)")
   }
}