Building an app with a document browser

At a glance

Project structure

Source bundle/
├── Document Browser/
│   ├── BrowserSceneDelegate.swift
│   ├── AppDelegate.swift
│   ├── TextDocument.swift
│   ├── DocumentBrowserViewController.swift
│   ├── TextDocumentViewController.swift
│   ├── Base.lproj/
│   │   ├── LaunchScreen.storyboard
│   │   └── Main.storyboard
│   └── Info.plist
├── Configuration/
│   └── SampleCode.xcconfig
└── Document Browser.xcodeproj/
    ├── .xcodesamplecode.plist
    └── project.pbxproj

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 6 project/configuration file(s) and 7 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["DocumentBrowserViewController"]
    N3["TextDocument"]
    N4["UIKit APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

Document Browser/AppDelegate.swift:15 — architecture anchor

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    func application(_ application: UIApplication,
                     didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]? = nil) -> Bool {
        return true
    }

}

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 UIKit.

Ownership and state

classDiagram
    BrowserSceneDelegate o-- UIWindow : window
    AppDelegate o-- UIWindow : window
    TextDocument o-- TextDocumentDelegate : delegate
    TextDocument *-- Progress : loadProgress

Ownership evidence

Document Browser/BrowserSceneDelegate.swift:17 — stored dependency or nearest verified ownership anchor

@available(iOS 13.0, *)
class BrowserSceneDelegate: UIResponder, UIWindowSceneDelegate {
    // ...
    var window: UIWindow?
    // ...
}

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.

No source-visible execution, scheduling, or synchronization boundary was found in the indexed source.

@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.

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

Document Browser/TextDocument.swift:16 — representative type boundary

protocol TextDocumentDelegate: AnyObject {
    func textDocumentEnableEditing(_ doc: TextDocument)
    // ...
}

The source explicitly defines local protocol relationships: TextDocumentViewController → TextDocumentDelegate.

Access control

Reference code

Document Browser/BrowserSceneDelegate.swift:47 — representative boundary

    private func openURLContext(_ urlContext: UIOpenURLContext) {
        // ...
            fatalError("*** The root view is not a document browser ***")
        // ...
    }

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: DocumentBrowserViewController, TextDocumentViewController; Delegate: AppDelegate, BrowserSceneDelegate, TextDocumentDelegate; Document: TextDocument.
• Protocols: TextDocumentDelegate.
• Methods: browserSceneSession, scene, openURLContext, application, textDocumentEnableEditing, textDocumentDisableEditing, textDocumentUpdateContent, textDocumentTransferBegan.
• Files: Document Browser/BrowserSceneDelegate.swift, Document Browser/AppDelegate.swift, Document Browser/TextDocument.swift, Document Browser/DocumentBrowserViewController.swift, Document Browser/TextDocumentViewController.swift.

Architecture takeaways

• AppDelegate is the main source-visible entry or composition anchor for this sample.
• Framework work reaches UIKit 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