NSOutlineView spacing between items is incorrect - swift

Question

I have an NSOutlineView, and the space between items 1 and 2 is greater than the spacing between all other items. These are group items. The outline view is very bare bones. Below is my code, and below that is an image of the issue I am referring to:
var sections: [SidebarSection] = [
SidebarSection(title: "Section 1", items: ["1", "2", "3", "4", "5"]),
SidebarSection(title: "Section 2", items: ["1", "2"]),
SidebarSection(title: "Section 3", items: ["1", "2"]),
SidebarSection(title: "Section 4", items: ["1", "2"]),
SidebarSection(title: "Section 5", items: ["1", "2"])]
private let outlineView: SidebarOutlineView = SidebarOutlineView()
extension SidebarViewController: NSOutlineViewDataSource {
func outlineView(_ outlineView: NSOutlineView, isItemExpandable item: Any) -> Bool {
return item is SidebarSection
}
func outlineView(_ outlineView: NSOutlineView, child index: Int, ofItem item: Any?) -> Any {
if let section = item as? SidebarSection {
return section.items[index]
}
return sections[index]
}
func outlineView(_ outlineView: NSOutlineView, numberOfChildrenOfItem item: Any?) -> Int {
if let section = item as? SidebarSection {
return section.items.count
}
return sections.count
}
}
extension SidebarViewController: NSOutlineViewDelegate {
func outlineView(_ outlineView: NSOutlineView, heightOfRowByItem item: Any) -> CGFloat {
return 30
}
func outlineView(_ outlineView: NSOutlineView, isGroupItem item: Any) -> Bool {
return item is SidebarSection
}
func outlineView(_ outlineView: NSOutlineView, viewFor tableColumn: NSTableColumn?, item: Any) -> NSView? {
let view = outlineView.makeView(withIdentifier: NSUserInterfaceItemIdentifier(rawValue: "SidebarPlaylistCell"), owner: self) as! SidebarPlaylistCell
view.wantsLayer = true
view.textLabel.stringValue = (item as? SidebarSection)?.title ?? ""
view.imgView.wantsLayer = true
view.imgView.layer?.backgroundColor = NSColor.red.cgColor
return view
}
}
extension SidebarViewController {
func layout() {
scrollView.translatesAutoresizingMaskIntoConstraints = false
view.addSubview(scrollView)
scrollView.leadingAnchor.constraint(equalTo: view.leadingAnchor).isActive = true
scrollView.topAnchor.constraint(equalTo: view.topAnchor).isActive = true
scrollView.trailingAnchor.constraint(equalTo: view.trailingAnchor).isActive = true
scrollView.bottomAnchor.constraint(equalTo: view.bottomAnchor).isActive = true
scrollView.documentView = outlineView
outlineView.headerView = nil
outlineView.delegate = self
outlineView.dataSource = self
outlineView.intercellSpacing = NSSize(width: 0, height: 0)
scrollView.hasVerticalScroller = true
scrollView.hasHorizontalScroller = false
scrollView.wantsLayer = true
view.layer?.backgroundColor = NSColor.blue.cgColor
}
}
final class SidebarOutlineView: NSOutlineView {
override init(frame frameRect: NSRect) {
super.init(frame: frameRect)
let column: NSTableColumn = NSTableColumn(identifier: NSUserInterfaceItemIdentifier("col1"))
column.isEditable = false
column.minWidth = 0
addTableColumn(column)
outlineTableColumn = column
register(NSNib(nibNamed: "SidebarPlaylistCell", bundle: nil), forIdentifier: NSUserInterfaceItemIdentifier(rawValue: "SidebarPlaylistCell"))
selectionHighlightStyle = .sourceList
indentationPerLevel = 6.0
}
required init?(coder: NSCoder) {
super.init(coder: coder)
}
}

Answer 1

This behavior can be controlled by a boolean flag floatsGroupRows, which is set to true by default. So by adding:
outlineView.floatsGroupRows = false
you get the desired behavior.
Documentation can be found here:
https://developer.apple.com/documentation/appkit/nstableview/1528624-floatsgrouprows?language=swift
A Boolean value indicating whether the table view draws grouped rows as if they are floating.
Quick Test
Meaning of floatGroupRows
The effect of floatsGroupRows can be seen better in an animated graphic. During a scroll operation, the current GroupItem remains floating on top: