Yes, there was an option I missed. NSTreeController seems to handle this really well, with a few small quirks. I had to add a 'rules' property to my rule. Simple extension: extension Rule { @objc public var rules: NSSet? { return self.passToLayer?.rules } } Setting up the binding was a little weird, as I've never done that in code before. Wound up with roughly this: @IBOutlet var ruleViewContainer:NSView! var ruleOutlineView:NSOutlineView = NSOutlineView() private var layerToShow:Layer private var treeController:NSTreeController = NSTreeController() ... override func viewWillAppear() { ... let outlineContainer = NSScrollView(frame:ruleViewContainer.bounds) outlineContainer.autoresizingMask = [.width, .height] outlineContainer.documentView = ruleOutlineView outlineContainer.hasVerticalScroller = true outlineContainer.hasHorizontalScroller = true ruleViewContainer.addSubview(outlineContainer) ruleOutlineView.usesAlternatingRowBackgroundColors = true ruleOutlineView.usesAutomaticRowHeights = true ruleOutlineView.delegate = self ruleOutlineView.dataSource = self ruleOutlineView.doubleAction = #selector(self.doubleClick) ruleOutlineView.target = self treeController.childrenKeyPath = "rules" treeController.bind(NSBindingName.content, to: layerToShow, withKeyPath: "rules", options: nil) ruleOutlineView.bind(NSBindingName.content, to: treeController, withKeyPath: "arrangedObjects", options: nil) } Now all the items in the NSOutlineView are of type NSTreeNode. This broke my existing drag-and-drop and outlineView(_ outlineView:, viewFor tableColumn:, item:). Easy enough to fix. Just wrap all the references to item like this: let representedItem = (item as! NSTreeNode).representedObject Then use representedItem just like you used item before. I handle the updates in my API interaction object, which then updates my Core Data store if the server confirms the attempted change was successful. The UI then updates. I still have a few weird glitches. Moved objects are sometimes out of order. That should be much easier to figure out, though.

Figured it out. I used a modified version of this NSImage+TintColor extension to create a swatch dictionary: let namedColors:[String] = [ "aquamarine", "black", "blue", ... } let myColorSwatches:[String:NSImage] = { (colorNames:[String]) -> [String:NSImage] in var toReturn:[String:NSImage] = [:] for colorName in colorNames { let image = NSImage(systemSymbolName: "rectangle.fill", accessibilityDescription: nil)! image.isTemplate = false image.lockFocus() NSColor(named: colorName)!.set() let imageRect = NSRect(origin: .zero, size: image.size) imageRect.fill(using: .sourceIn) image.unlockFocus() toReturn[colorName] = image } return toReturn }(namedColors) ... which I can then reference in my SwiftUI Picker: Picker("Color:", selection: pickerColor) { ForEach(namedColors, id: \.self) { colorName in HStack { Image(nsImage: myColorSwatches[colorName]!) Text(colorName) } } } And just as a reminder in case anybody else wants to do this, I have a color set defined in my Assets.xcassets for each named color.