Disclosure buttons missing in code only NSOutlineView - cocoa

Question

I'm attempting to construct code-only NSOutlineView in Swift playground, and I'm coming to grief trying to display the disclosure buttons.
At the moment the result looks like this:
But I am expecting something more like this:
Here's the code I have so far.
// Requires XCode 7.3.1
import Cocoa
import XCPlayground
let FILENAME_COLUMN = "FileName2"
public class Node
{
init (_ description: String, _ children: [Node]) {
self.description = description
self.children = children
}
convenience init (_ description: String) {
self.init(description, [])
}
public var children : [Node] = []
public var description: String = ""
}
func makeOutline() -> NSOutlineView {
let outline = NSOutlineView(frame: NSMakeRect(0, 0, 250, 150))
let fileNameColumn = NSTableColumn(identifier: FILENAME_COLUMN)
fileNameColumn.title = "File Name"
fileNameColumn.width = 200
outline.addTableColumn(fileNameColumn)
outline.selectionHighlightStyle = .Regular
return outline
}
func makeOutlineDelegate() -> NSOutlineViewDelegate {
class OutlineViewDelegate : NSObject, NSOutlineViewDelegate {
#objc func outlineView(outlineView: NSOutlineView, shouldShowOutlineCellForItem item: AnyObject) -> Bool {
return true
}
#objc func outlineView(outlineView: NSOutlineView, shouldExpandItem item: AnyObject) -> Bool {
return true;
}
#objc func outlineView(outlineView: NSOutlineView, viewForTableColumn tableColumn: NSTableColumn?, item: AnyObject) -> NSView? {
let columnIdentifier = tableColumn!.identifier
if let recycledCell = outlineView.makeViewWithIdentifier(columnIdentifier, owner: self) as? NSTableCellView {
return recycledCell
}
let newCell = NSTableCellView(frame: NSMakeRect(0, 0, 150, outlineView.rowHeight))
newCell.identifier = columnIdentifier
newCell.autoresizesSubviews = true
let imageField = NSImageView(frame: NSMakeRect(0, 0, 150, outlineView.rowHeight))
newCell.addSubview(imageField)
newCell.imageView = imageField
let textField = NSTextField(frame: NSMakeRect(0, 0, 150, outlineView.rowHeight))
newCell.addSubview(textField)
newCell.textField = textField
textField.bordered = false
textField.drawsBackground = false
textField.bind(NSValueBinding,
toObject: newCell,
withKeyPath: "objectValue",
options: nil)
return newCell
}
}
return OutlineViewDelegate()
}
func makeOutlineDataSource(store: [Node]) -> NSOutlineViewDataSource {
class OutlineViewDataSource : NSObject, NSOutlineViewDataSource {
var store : [Node]
init(store:[Node]) {
self.store = store
}
#objc func outlineView(outlineView: NSOutlineView, isItemExpandable item: AnyObject) -> Bool {
if item is [Node] {
return true
}
if let node = item as? Node {
return node.children.count > 0
}
return true
}
#objc func outlineView(outlineView: NSOutlineView, objectValueForTableColumn tableColumn: NSTableColumn?, byItem item: AnyObject?) -> AnyObject? {
if let node = item as? Node {
return node.description
}
return nil
}
#objc func outlineView(outlineView: NSOutlineView, child index: Int, ofItem item: AnyObject?) -> AnyObject {
if (item == nil) {
return store[index]
}
if let nodeArray = item as? [Node] {
return nodeArray[index]
}
if let node = item as? Node {
return node.children[index]
}
return Node("WRONG")
}
#objc func outlineView(outlineView: NSOutlineView, numberOfChildrenOfItem item: AnyObject?) -> Int {
if (item == nil) {
return store.count;
}
if let nodeArray = item as? [Node] {
return nodeArray.count
}
if let node = item as? Node {
return node.children.count
}
return 0
}
}
return OutlineViewDataSource(store: store)
}
let store = [
Node("Dev", [
Node("svc_sql_dev"),
Node("svc_app_dev")
]),
Node("Test",[
Node("svc_sql_test"),
Node("svc_app_test")
]),
Node("UAT",[
Node("svc_sql_uat"),
Node("svc_app_uat")
]),
Node("Prod",[
Node("svc_sql_prod"),
Node("svc_app_prod")
])
]
let outline = makeOutline()
let dataSource = makeOutlineDataSource(store)
let outlineDelegate = makeOutlineDelegate()
outline.setDataSource(dataSource)
outline.setDelegate(outlineDelegate)
outline.expandItem(outline.itemAtRow(4), expandChildren: true)
outline.expandItem(outline.itemAtRow(3), expandChildren: true)
outline.expandItem(outline.itemAtRow(2), expandChildren: true)
outline.expandItem(outline.itemAtRow(0), expandChildren: true)
let container = NSScrollView(
frame: NSMakeRect(0, 0, 400, 160))
container.documentView = outline
container.hasVerticalScroller = true;
//dispatch_async(dispatch_get_main_queue(), {
// outline.expandItem(nil, expandChildren: true)
//})
XCPlaygroundPage.currentPage.liveView = container
Update (with solution)
Setting the column as outlineColumn is required:
outline.outlineTableColumn = fileNameColumn