Building a multidevice workout app

At a glance

Project structure

Source bundle/
├── MirroringWorkoutsSample Watch App/
│   ├── MirroringWorkoutsSampleApp.swift
│   ├── PagingView.swift
│   ├── SummaryView.swift
│   ├── ActivityRingsView.swift
│   ├── AppDelegate.swift
│   ├── ControlsView.swift
│   └── MetricsView.swift
├── MirroringWorkoutsSample/
│   ├── MirroringWorkoutsSampleApp.swift
│   ├── ChartView.swift
│   └── SummaryView.swift
└── Shared/
    ├── WorkoutManager.swift
    └── ElapsedTimeView.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 6 project/configuration file(s) and 26 source declaration(s).

Overall architecture

flowchart LR
    Bundle["Sample bundle"]
    V1["MirroringWorkoutsSample Watch App"]
    V2["MirroringWorkoutsSample"]
    Boundary["HealthKit / HealthKitUI APIs"]
    Bundle --> V1
    V1 --> Boundary
    Bundle --> V2
    V2 --> Boundary

Reference code

MirroringWorkoutsSample Watch App/MirroringWorkoutsSampleApp.swift:10 — architecture anchor

@main
struct MirroringWorkoutsSampleWatchApp: App {
    @WKApplicationDelegateAdaptor(AppDelegate.self) private var appDelegate
    private let workoutManager = WorkoutManager.shared

    @SceneBuilder var body: some Scene {
        WindowGroup {
            PagingView()
                .environmentObject(workoutManager)
        }
    }
}

Interpretation

The branches represent separate entry-bearing project variants in the downloaded bundle, not runtime calls between those variants. Each branch is intentionally collapsed at the documented framework boundary; the detailed target-local flow remains in the cited files. Ownership is claimed only where the next section cites a stored property or assignment.

Ownership and state

classDiagram
    SessionSateChange o-- HKWorkoutSessionState : newState
    SessionSateChange *-- Date : date
    SessionSateChange o-- HKWorkoutSessionState : sessionState
    SessionSateChange *-- Double : heartRate

Ownership evidence

Shared/WorkoutManager.swift:15 — stored dependency or nearest verified ownership anchor

    struct SessionSateChange {
        let newState: HKWorkoutSessionState
        let date: Date
    }

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

MirroringWorkoutsSample Watch App/ActivityRingsView.swift:23 — representative execution boundary

            DispatchQueue.main.async {
                activityRingsObject.setActivitySummary(summaries?.first, animated: true)
            }

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

MirroringWorkoutsSample Watch App/MirroringWorkoutsSampleApp.swift:11 — representative type boundary

@main
struct MirroringWorkoutsSampleWatchApp: App {
    @WKApplicationDelegateAdaptor(AppDelegate.self) private var appDelegate
    // ...
}

No local protocol conformance is claimed as protocol-oriented design; external framework conformances are listed only as dependencies.

Access control

Reference code

MirroringWorkoutsSample Watch App/ActivityRingsView.swift:13 — representative boundary

struct ActivityRingsView: WKInterfaceObjectRepresentable {
    @Environment(\.calendar) private var calendar
    // ...
}

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: App: MirroringWorkoutsSampleApp, MirroringWorkoutsSampleWatchApp; Delegate: AppDelegate; Manager: WorkoutManager; View: ActivityRingsView, ChartView, ControlsView, ElapsedTimeView, GridItemView.
• Protocols: no local protocol declaration in the scanned source.
• Methods: consumeSessionStateChange, resetWorkout, sendData, updateForStatistics, workoutSession, displayMetricsView, summaryListView, updateLineEntries.
• Files: MirroringWorkoutsSample/MirroringWorkoutsSampleApp.swift, Shared/WorkoutManager.swift, MirroringWorkoutsSample Watch App/PagingView.swift, MirroringWorkoutsSample Watch App/SummaryView.swift, MirroringWorkoutsSample/ChartView.swift, MirroringWorkoutsSample/SummaryView.swift.

Architecture takeaways

• MirroringWorkoutsSampleApp is the main source-visible entry or composition anchor for this sample.
• Framework work reaches SwiftUI, HealthKit, Charts, HealthKitUI 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.
• The source does not justify labeling the design protocol-oriented.

Source map

• Official Apple documentation