Monitoring location changes with Core Location

At a glance

Project structure

Source bundle/
├── LocationMonitorSampleApp/
│   ├── LocationMonitorSampleApp.swift
│   ├── ContentView.swift
│   ├── AppDelegate.swift
│   └── Info.plist
├── Configuration/
│   └── SampleCode.xcconfig
└── LocationMonitorSampleApp.xcodeproj/
    ├── .xcodesamplecode.plist
    └── project.pbxproj

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 5 source declaration(s).

Overall architecture

flowchart LR
    N1["LocationMonitorSampleApp"]
    N2["ContentView"]
    N3["ObservableMonitorModel"]
    N4["CoreLocation APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

LocationMonitorSampleApp/LocationMonitorSampleApp.swift:10 — architecture anchor

@main
struct LocationMonitorSampleApp: App {
    @UIApplicationDelegateAdaptor(AppDelegate.self) var appDelegate

    var body: some Scene {
        WindowGroup {
            ContentView()
        }
    }
}

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 Core Location.

Ownership and state

classDiagram
    ContentView *-- CLLocationCoordinate2D : appleParkLocation
    ContentView *-- UUID : testBeaconId
    ObservableMonitorModel *-- ObservableMonitorModel : shared
    ObservableMonitorModel o-- CLMonitor : monitor

Ownership evidence

LocationMonitorSampleApp/ContentView.swift:12 — stored dependency or nearest verified ownership anchor

let appleParkLocation = CLLocationCoordinate2D(latitude: 37.3346, longitude: -122.0090)

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

LocationMonitorSampleApp/ContentView.swift:30 — representative execution boundary

@MainActor
public class ObservableMonitorModel: ObservableObject {
    // ...
    static let shared = ObservableMonitorModel()
    // ...
}

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

LocationMonitorSampleApp/LocationMonitorSampleApp.swift:11 — representative type boundary

@main
struct LocationMonitorSampleApp: App {
    @UIApplicationDelegateAdaptor(AppDelegate.self) var appDelegate
    // ...
}

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

Access control

Reference code

LocationMonitorSampleApp/ContentView.swift:38 — representative boundary

@MainActor
public class ObservableMonitorModel: ObservableObject {
    // ...
    public var monitor: CLMonitor?
    // ...
}

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

Main application flow

One launch starts a long-lived monitor task that registers conditions, restores their last events, and then reduces each asynchronous event into observable UI rows.

sequenceDiagram
    participant System as UIApplication
    participant App as AppDelegate
    participant Model as ObservableMonitorModel
    participant Monitor as CLMonitor
    participant UI as ContentView
    System-->>App: didFinishLaunching
    App->>Model: startMonitoringConditions()
    Model->>Monitor: Create named monitor
    Model->>Monitor: Add geographic and beacon conditions
    loop existing identifiers
        Model->>Monitor: record(for: identifier)
        Monitor-->>Model: lastEvent
    end
    loop asynchronous condition events
        Monitor-->>Model: events sequence yields event
        Model->>Monitor: read prior lastEvent
        Model-->>UI: Update published UIRows
    end

Reference code

LocationMonitorSampleApp/ContentView.swift:77 — startMonitoringConditions

    func startMonitoringConditions() {
        Task {
            print("Set up monitor")
            monitor = await CLMonitor(monitorName)

            await monitor!.add(getCircularGeographicCondition(), identifier: "ApplePark")
            await monitor!.add(getBeaconIdentityCondition(), identifier: "TestBeacon")
            for identifier in await monitor!.identifiers {
                guard let lastEvent = await monitor!.record(for: identifier)?.lastEvent else { continue }
                UIRows[identifier] = [lastEvent]
            }
            for try await event in await monitor!.events {
                // While handling the most recent event, the last event is still updating
                // and shows the prior state, allowing you to reference both.
                guard let lastEvent = await monitor!.record(for: event.identifier)?.lastEvent else { continue }

                if event.state == lastEvent.state {
                    // If the event state is the same as the previous state, the only new information is in diagnostics.
                    // Because the event isn't a new state, don't record it in your UI.
                    // Because you respond to service session diagnostics, you don't need to also worry about the ones delivered by the monitor.
                    continue
                }
                UIRows[event.identifier] = [event]
                UIRows[event.identifier]?.append(lastEvent)
            }
        }
    }

Naming conventions

• Types: App: LocationMonitorSampleApp; Delegate: AppDelegate; Model: ObservableMonitorModel; View: ContentView, ErrorView.
• Protocols: no local protocol declaration in the scanned source.
• Methods: without, startAuthSession, startMonitoringConditions, updateRecords, getCircularGeographicCondition, getBeaconIdentityCondition, application.
• Files: LocationMonitorSampleApp/LocationMonitorSampleApp.swift, LocationMonitorSampleApp/ContentView.swift, LocationMonitorSampleApp/AppDelegate.swift.

Architecture takeaways

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