Navigating Hierarchical Data Using Outline and Split Views

At a glance

Project structure

Source bundle/
└── SourceView/
    ├── OutlineViewController.swift
    ├── AppDelegate.swift
    ├── IconViewController.swift
    ├── SplitViewController.swift
    ├── WindowViewController.swift
    ├── FileViewController.swift
    ├── ImageViewController.swift
    ├── OutlineView.swift
    ├── SeparatorView.swift
    ├── WindowController.swift
    ├── NodePasteboardWriter.swift
    └── OutlineViewController+Delegate.swift

Structure observations

• Architecturally prominent files are ranked from entry points and role-named declarations; resource-only paths are omitted.
• Primary languages: Swift.
• The verified tree contains 7 project/configuration file(s) and 23 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["FileViewController"]
    N3["Cocoa / UniformTypeIdentifiers APIs"]
    N1 --> N2
    N2 --> N3

Reference code

SourceView/AppDelegate.swift:10 — architecture anchor

@NSApplicationMain
class AppDelegate: NSObject, NSApplicationDelegate {

}

Interpretation

The arrows summarize the source-visible entry, role-named types or folders, and framework direction; when nodes come from structural folders, the sequence is a high-level interpretation rather than proof that every adjacent node calls the next. Ownership is claimed only where the next section cites a stored property or assignment. The diagram is intentionally limited to the dominant path into AppKit.

Ownership and state

classDiagram
    NameConstants *-- NSLocalizedString : untitled
    NameConstants *-- NSLocalizedString : places
    NameConstants *-- NSLocalizedString : pictures
    NotificationNames o-- NSTreeController : treeController

Ownership evidence

SourceView/OutlineViewController.swift:18 — stored dependency or nearest verified ownership anchor

    struct NameConstants {
        // ...
        static let untitled = NSLocalizedString("untitled string", comment: "")
        // ...
    }

Composition arrows indicate a source-visible construction expression or locally owned value state; aggregation means the owner stores or receives a dependency without proving exclusive lifetime ownership.

Concurrency, scheduling, and thread safety

Evidence limit: actor isolation, async/await, or Task creation does not by itself prove background-thread execution; Sendable conformance alone does not prove thread-safe mutation.

@MainActor/MainActor.run, DispatchQueue.main, and RunLoop.main are reported as distinct isolation, queue, and event-loop mechanisms. A plain Task is kept separate from Task.detached; neither is labeled as a background thread.

Reference code

SourceView/IconViewController.swift:28 — representative execution boundary

            DispatchQueue.global(qos: .default).async {
                // Asynchronously fetch the contents of this URL.
                self.gatherContents(self.url!)
            }

State propagation, frameworks, and dependencies

Evidence limit: an import proves a source-level compilation dependency at the cited line; it does not prove runtime use, architectural adoption, or whether a Swift package is a direct application dependency.

receive(on:) describes downstream delivery scheduling, while subscribe(on:) describes upstream subscription/request/cancel scheduling. An import Combine alone establishes neither behavior nor a Store, reducer, Redux, or other application architecture.

Class and protocol design

SourceView/OutlineViewController+ContextalMenu.swift:13 — representative type boundary

protocol CustomMenuDelegate: AnyObject {

    // Construct a context menu from the current selected rows.
    func outlineViewMenuForRows(_ outlineView: NSOutlineView, rows: IndexSet) -> NSMenu?
}

The source explicitly defines local protocol relationships: OutlineViewController → CustomMenuDelegate.

Access control

Reference code

SourceView/FileViewController.swift:12 — representative boundary

class FileViewController: NSViewController {
    // ...
    @IBOutlet private var fileIcon: NSImageView!
    // ...
}

Swift declarations without a modifier are internal; explicit private, fileprivate, private(set), public, or open entries above are interpreted by language semantics. Objective-C/C samples instead rely on header and implementation boundaries, which are not equivalent to Swift lexical privacy.

Logic ownership and placement

Design patterns

Naming conventions

• Types: Controller: FileViewController, IconViewController, ImageViewController, OutlineViewController, SplitViewController; Delegate: AppDelegate, CustomMenuDelegate; View: OutlineView, SeparatorView.
• Protocols: CustomMenuDelegate.
• Methods: viewDidLoad, selectParentFromSelection, addFileSystemObject, addFileSystemObjects, addGroupNode, addNode, addPlacesGroup, addPicturesGroup.
• Files: SourceView/OutlineViewController.swift, SourceView/AppDelegate.swift, SourceView/IconViewController.swift, SourceView/SplitViewController.swift, SourceView/WindowViewController.swift, SourceView/FileViewController.swift.

Architecture takeaways

• AppDelegate is the main source-visible entry or composition anchor for this sample.
• Framework work reaches Cocoa, UniformTypeIdentifiers through a deliberately small high-level chain; the detailed API graph remains inside the cited implementation files.
• Stored-property evidence identifies lifecycle collaboration; it does not by itself prove exclusive object ownership.
• Access-control conclusions separate verified language visibility from the likely design rationale.
• Local protocol relationships provide an explicit substitution boundary.

Source map

• Official Apple documentation