OutlineView Example

ViewController.swift

import Cocoa

class ViewController: NSViewController {

    internal lazy var outlineView: NSOutlineView = {
        let outlineView = NSOutlineView()
        outlineView.usesAutomaticRowHeights = true

        let column = NSTableColumn(identifier: .init(rawValue: "TestColumn"))
        outlineView.addTableColumn(column)
        outlineView.outlineTableColumn = column

        outlineView.headerView = nil
        outlineView.backgroundColor = .clear
        outlineView.indentationPerLevel = 16
        outlineView.allowsEmptySelection = false
        outlineView.refusesFirstResponder = true

        return outlineView
    }()

    override func viewDidLoad() {
        super.viewDidLoad()

        let scrollView = NSScrollView()
        scrollView.translatesAutoresizingMaskIntoConstraints = false
        scrollView.drawsBackground = false
        view.addSubview(scrollView)

        NSLayoutConstraint.activate([
            scrollView.topAnchor.constraint(equalTo: view.topAnchor),
            scrollView.bottomAnchor.constraint(equalTo: view.bottomAnchor),
            scrollView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            scrollView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
        ])

        scrollView.documentView = outlineView

        outlineView.dataSource = self
        outlineView.delegate = self
    }

    override var representedObject: Any? {
        didSet {
        // Update the view, if already loaded.
        }
    }
}

extension ViewController: NSOutlineViewDataSource {

    func outlineView(_ outlineView: NSOutlineView, numberOfChildrenOfItem item: Any?) -> Int {
        item == nil ? 10 : 0
    }

    func outlineView(_ outlineView: NSOutlineView, isItemExpandable item: Any) -> Bool {
        false
    }

    func outlineView(_ outlineView: NSOutlineView, child index: Int, ofItem item: Any?) -> Any {
        "Item \(index)"
    }
}

extension ViewController: NSOutlineViewDelegate {

    func outlineView(_ outlineView: NSOutlineView, viewFor tableColumn: NSTableColumn?, item: Any) -> NSView? {
        var cellView = outlineView.makeView(withIdentifier: .init(rawValue: "CellView"), owner: nil) as? CellView
        if cellView == nil {
            cellView = CellView(frame: .zero)
            cellView?.identifier = .init("CellView")
            cellView?.textField?.isEditable = true
            cellView?.textField?.stringValue = (item as? String) ?? ""
        }
        return cellView
    }
}

class CellView: NSTableCellView {

    override init(frame frameRect: NSRect) {
        super.init(frame: frameRect)

        let textField = NSTextField()
        textField.translatesAutoresizingMaskIntoConstraints = false
        textField.font = .controlContentFont(ofSize: 14)
        textField.textColor = .controlTextColor
        textField.isBordered = false
        textField.backgroundColor = .clear
        textField.focusRingType = .none
        textField.usesSingleLineMode = true
        addSubview(textField)

        NSLayoutConstraint.activate([
            textField.topAnchor.constraint(equalTo: topAnchor),
            textField.bottomAnchor.constraint(equalTo: bottomAnchor),
            textField.leadingAnchor.constraint(equalTo: leadingAnchor),
            textField.trailingAnchor.constraint(equalTo: trailingAnchor),
        ])
        self.textField = textField
    }

    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}