Build a workout app for Apple Watch

At a glance

Project structure

Source bundle/
├── MyWorkouts WatchKit Extension/
│   ├── MyWorkoutsApp.swift
│   ├── Views/
│   │   ├── ElapsedTimeView.swift
│   │   ├── MetricsView.swift
│   │   ├── SessionPagingView.swift
│   │   ├── SummaryView.swift
│   │   ├── ControlsView.swift
│   │   ├── StartView.swift
│   │   └── ActivityRingsView.swift
│   ├── ComplicationController.swift
│   └── Controller/
│       └── WorkoutManager.swift
├── Configuration/
│   └── SampleCode.xcconfig
└── MyWorkouts WatchKit App/
    └── Info.plist

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 14 source declaration(s).

Overall architecture

flowchart LR
    N1["MyWorkoutsApp"]
    N2["StartView"]
    N3["WorkoutManager"]
    N4["HealthKit APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

MyWorkouts WatchKit Extension/MyWorkoutsApp.swift:10 — architecture anchor

@main
struct MyWorkoutsApp: App {
    @StateObject private var workoutManager = WorkoutManager()

    @SceneBuilder var body: some Scene {
        WindowGroup {
            NavigationView {
                StartView()
            }
            .sheet(isPresented: $workoutManager.showingSummaryView) {
                SummaryView()
            }
            .environmentObject(workoutManager)
        }
    }
}

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 HealthKit.

Ownership and state

classDiagram
    MyWorkoutsApp *-- WorkoutManager : workoutManager
    ElapsedTimeView o-- TimeInterval : elapsedTime
    ElapsedTimeView *-- Bool : showSubseconds
    ElapsedTimeView *-- ElapsedTimeFormatter : timeFormatter

Ownership evidence

MyWorkouts WatchKit Extension/MyWorkoutsApp.swift:12 — stored dependency or nearest verified ownership anchor

@main
struct MyWorkoutsApp: App {
    @StateObject private var workoutManager = WorkoutManager()
    // ...
}

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

MyWorkouts WatchKit Extension/Controller/WorkoutManager.swift:121 — representative execution boundary

        DispatchQueue.main.async {
            // ...
            case HKQuantityType.quantityType(forIdentifier: .heartRate):
            // ...
        }

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

MyWorkouts WatchKit Extension/MyWorkoutsApp.swift:11 — representative type boundary

@main
struct MyWorkoutsApp: App {
    @StateObject private var workoutManager = WorkoutManager()
    // ...
}

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

Access control

Reference code

MyWorkouts WatchKit Extension/MyWorkoutsApp.swift:12 — representative boundary

@main
struct MyWorkoutsApp: App {
    @StateObject private var workoutManager = WorkoutManager()
    // ...
}

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: MyWorkoutsApp; Controller: ComplicationController; Manager: WorkoutManager; View: ActivityRingsView, ControlsView, ElapsedTimeView, MetricsView, SessionPagingView.
• Protocols: no local protocol declaration in the scanned source.
• Methods: string, entries, displayMetricsView, getComplicationDescriptors, handleSharedComplicationDescriptors, getTimelineEndDate, getPrivacyBehavior, getCurrentTimelineEntry.
• Files: MyWorkouts WatchKit Extension/MyWorkoutsApp.swift, MyWorkouts WatchKit Extension/Views/ElapsedTimeView.swift, MyWorkouts WatchKit Extension/Views/MetricsView.swift, MyWorkouts WatchKit Extension/Views/SessionPagingView.swift, MyWorkouts WatchKit Extension/Views/SummaryView.swift, MyWorkouts WatchKit Extension/Views/ControlsView.swift.

Architecture takeaways

• MyWorkoutsApp is the main source-visible entry or composition anchor for this sample.
• Framework work reaches SwiftUI, HealthKit, WatchKit, ClockKit 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