Backyard Birds: Building an app with SwiftData and widgets

At a glance

Project structure

Source bundle/
├── Multiplatform/
│   ├── BackyardBirdsApp.swift
│   └── Backyards/
│       └── BackyardDetailView.swift
├── Watch/
│   └── BackyardBirdsWatchApp.swift
├── Widgets/
│   ├── WidgetsBundle.swift
│   └── Backyard/
│       ├── BackyardSnapshotTimelineProvider.swift
│       └── BackyardWidgetView.swift
├── BackyardBirdsData/
│   └── General/
│       └── SeededRandomGenerator.swift
└── BackyardBirdsUI/
    ├── Backyard/
    │   ├── BackyardSkyView.swift
    │   ├── BackyardViewport.swift
    │   └── BackyardViewportLayout.swift
    ├── PlantView.swift
    └── Visitors/
        └── RecentBackyardVisitorsView.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 135 source declaration(s).

Overall architecture

flowchart LR
    Bundle["Sample bundle"]
    V1["Multiplatform"]
    V2["Watch"]
    V3["Widgets"]
    Boundary["SwiftUI APIs"]
    Bundle --> V1
    V1 --> Boundary
    Bundle --> V2
    V2 --> Boundary
    Bundle --> V3
    V3 --> Boundary

Reference code

Multiplatform/BackyardBirdsApp.swift:12 — architecture anchor

@main
struct BackyardBirdsApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
                .backyardBirdsShop()
                .backyardBirdsDataContainer()
        }
    }
}

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
    BackyardSnapshot o-- Backyard : backyard
    BackyardSnapshot o-- Bird : visitingBird
    BackyardSnapshot o-- TimeInterval : visitingBirdDuration
    BackyardSnapshot o-- TimeInterval : timeInterval

Ownership evidence

BackyardBirdsData/Backyards/BackyardSnapshot.swift:11 — stored dependency or nearest verified ownership anchor

public struct BackyardSnapshot {
    public var backyard: Backyard
    // ...
}

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

BackyardBirdsData/General/ModelPreview.swift:44 — representative execution boundary

                    Task {
                        try await Task.sleep(for: .seconds(1))
                        waitedToShowIssue = 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

Multiplatform/BackyardBirdsApp.swift:13 — representative type boundary

@main
struct BackyardBirdsApp: App {
    // ...
            ContentView()
    // ...
}

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

Access control

Reference code

BackyardBirdsData/Account/Account+DataGeneration.swift:12 — representative boundary

private let logger = Logger(subsystem: "BackyardBirdsData", category: "Account Generation")

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: BackyardBirdsApp, BackyardBirdsWatchApp; Generator: SeededRandomGenerator; Provider: BackyardSnapshotTimelineProvider; View: AppTabView, BackyardDetailView, BackyardSkyView, BackyardSnapshotWidgetView, BackyardTabView.
• Protocols: no local protocol declaration in the scanned source.
• Methods: backyards, placeholder, snapshot, timeline, recommendations, next, body, backyardViewportContent.
• Files: Multiplatform/BackyardBirdsApp.swift, Watch/BackyardBirdsWatchApp.swift, Widgets/WidgetsBundle.swift, Widgets/Backyard/BackyardSnapshotTimelineProvider.swift, Widgets/Backyard/BackyardWidgetView.swift, BackyardBirdsData/General/SeededRandomGenerator.swift.

Architecture takeaways

• BackyardBirdsApp is the main source-visible entry or composition anchor for this sample.
• Framework work reaches SwiftUI, SwiftData, BackyardBirdsData, BackyardBirdsUI 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