Integrating CarPlay with Your Music App

At a glance

Project structure

Source bundle/
├── CarPlayMusic/
│   ├── App Lifecycle/
│   │   ├── AppDelegate.swift
│   │   ├── PlayerController.swift
│   │   ├── LoggerViewController.swift
│   │   ├── LoggerWindowSceneDelegate.swift
│   │   └── TemplateApplicationSceneDelegate.swift
│   ├── Apple Music/
│   │   ├── AppleMusicAPIController.swift
│   │   ├── AppleMusicAPIStructures.swift
│   │   ├── MediaPlayerUtilities.swift
│   │   └── DateDecoder.swift
│   ├── Helpers/
│   │   └── Logger.swift
│   └── Template Manager/
│       └── TemplateManager.swift
└── CarPlayMusicIntent/
    └── IntentHandler.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 8 project/configuration file(s) and 60 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["AppleMusicAPIController"]
    N3["NowPlayingViewModel"]
    N4["IntentHandler"]
    N5["CarPlay APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4
    N4 --> N5

Reference code

CarPlayMusic/App Lifecycle/AppDelegate.swift:14 — architecture anchor

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    // ...
    func applicationDidBecomeActive(_ application: UIApplication) {
        MemoryLogger.shared.appendEvent("Application did become active.")
    }
    // ...
}

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 CarPlay.

Ownership and state

classDiagram
    AppleMusicAPIController *-- AppleMusicAPIController : sharedController
    AppleMusicAPIController *-- Bool : useAppleMusic
    AppleMusicAPIController *-- Bool : allowExplicitContent
    AppleMusicAPIController *-- TokenStorage : tokenStorage

Ownership evidence

CarPlayMusic/Apple Music/AppleMusicAPIController.swift:22 — stored dependency or nearest verified ownership anchor

class AppleMusicAPIController {
    // ...
    static let sharedController = AppleMusicAPIController()
    // ...
}

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

CarPlayMusic/App Lifecycle/AppDelegate.swift:44 — representative execution boundary

        DispatchQueue.global(qos: .userInitiated).async {
            // ...
            let context = INMediaUserContext()
            // ...
        }

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

CarPlayMusic/Helpers/Logger.swift:26 — representative type boundary

protocol LoggerDelegate: AnyObject {

    /// The logger has received a new event.
    func loggerDidAppendEvent()
}

The source explicitly defines local protocol relationships: MemoryLogger → Logger, LoggerViewController → LoggerDelegate.

Access control

Reference code

CarPlayMusic/App Lifecycle/AppDelegate.swift:136 — representative boundary

    private func registerForSpotlight(mediaItem: INMediaItem, identifier: String) {
        // ...
            return type == .playlist ? "MPMediaGrouping.playlist" :
        // ...
    }

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: AppleMusicAPIController, LoggerViewController, PlayerController; Delegate: AppDelegate, LoggerDelegate, LoggerWindowSceneDelegate, TemplateApplicationSceneDelegate; Handler: IntentHandler; Manager: TemplateManager; ViewModel: NowPlayingViewModel.
• Protocols: LoggerDelegate, Logger.
• Methods: applicationDidBecomeActive, applicationWillResignActive, applicationDidEnterBackground, applicationWillEnterForeground, applicationWillTerminate, application, resolveTerm, handle.
• Files: CarPlayMusic/App Lifecycle/AppDelegate.swift, CarPlayMusic/Apple Music/AppleMusicAPIController.swift, CarPlayMusic/App Lifecycle/PlayerController.swift, CarPlayMusic/Apple Music/MediaPlayerUtilities.swift, CarPlayMusic/App Lifecycle/LoggerViewController.swift, CarPlayMusic/App Lifecycle/LoggerWindowSceneDelegate.swift.

Architecture takeaways

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