Maintaining a local copy of server data

At a glance

Project structure

Source bundle/
└── DataCache/
    ├── DataCacheApp.swift
    ├── Model/
    │   ├── ViewModel.swift
    │   ├── GeoFeatureCollection.swift
    │   ├── Location.swift
    │   └── Quake.swift
    ├── Detail/
    │   ├── MapView.swift
    │   └── QuakeMarker.swift
    ├── Navigation/
    │   ├── ContentView.swift
    │   ├── SortButton.swift
    │   ├── DeleteButton.swift
    │   └── RefreshButton.swift
    └── Preview Content/
        └── ModelContainerPreviews.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 4 project/configuration file(s) and 22 source declaration(s).

Overall architecture

flowchart LR
    N1["DataCacheApp"]
    N2["ContentView"]
    N3["ViewModel"]
    N4["SwiftData APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

DataCache/DataCacheApp.swift:12 — architecture anchor

@main
struct DataCacheApp: App {
    @State private var viewModel = ViewModel()

    var body: some Scene {
        WindowGroup {
            ContentView()
                .environment(viewModel)
        }
        .modelContainer(for: Quake.self)
    }
}

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 SwiftData.

Ownership and state

classDiagram
    DataCacheApp *-- ViewModel : viewModel
    ViewModel o-- SortParameter : sortParameter
    ViewModel o-- SortOrder : sortOrder
    ViewModel *-- String : searchText

Ownership evidence

DataCache/DataCacheApp.swift:14 — stored dependency or nearest verified ownership anchor

@main
struct DataCacheApp: App {
    @State private var viewModel = ViewModel()
    // ...
}

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

DataCache/Model/GeoFeatureCollection.swift:84 — representative execution boundary

    static func fetchFeatures() async throws -> GeoFeatureCollection {
        // ...
        let url = URL(string: "https://earthquake.usgs.gov/earthquakes/feed/v1.0/summary/all_day.geojson")!
        // ...
    }

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

DataCache/DataCacheApp.swift:13 — representative type boundary

@main
struct DataCacheApp: App {
    @State private var viewModel = ViewModel()
    // ...
}

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

Access control

Reference code

DataCache/DataCacheApp.swift:14 — representative boundary

@main
struct DataCacheApp: App {
    @State private var viewModel = ViewModel()
    // ...
}

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: DataCacheApp; View: ContentView, MapView; ViewModel: ViewModel.
• Protocols: no local protocol declaration in the scanned source.
• Methods: update, fetchFeatures, distance.
• Files: DataCache/DataCacheApp.swift, DataCache/Model/ViewModel.swift, DataCache/Model/GeoFeatureCollection.swift, DataCache/Detail/MapView.swift, DataCache/Navigation/ContentView.swift, DataCache/Detail/QuakeMarker.swift.

Architecture takeaways

• DataCacheApp is the main source-visible entry or composition anchor for this sample.
• Framework work reaches SwiftUI, SwiftData, MapKit, CoreLocation 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