Continuing User Activities with Handoff

At a glance

Project structure

Source bundle/
├── HandoffMapViewer/
│   ├── HandoffMapViewerIOS/
│   │   ├── AppDelegate.swift
│   │   ├── MapViewController.swift
│   │   └── StoreDetailViewController.swift
│   ├── HandoffMapViewerMac/
│   │   ├── AppDelegate.swift
│   │   ├── MapViewController.swift
│   │   └── StoreDetailViewController.swift
│   └── Shared sources/
│       ├── AppleStore.swift
│       ├── AppleStoreAnnotation.swift
│       ├── AppleStoreDirectory.swift
│       ├── InitialMapRegionState.swift
│       └── NSUserActivity+HandoffMapViewer.swift
└── Configuration/
    └── SampleCode.xcconfig

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 10 project/configuration file(s) and 10 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["MapViewController"]
    N3["AppleStore"]
    N4["MapKit / Cocoa APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

HandoffMapViewer/HandoffMapViewerIOS/AppDelegate.swift:10 — architecture anchor

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    // When Handoff launches the app, get the window's content view controller and pass it to
    // the resorationHandler. This results in the view controller receiving the activity in restoreUserActivityState(_:).
    func application(_ application: UIApplication, continue userActivity: NSUserActivity,
                     restorationHandler: @escaping ([UIUserActivityRestoring]?) -> Void) -> Bool {
        guard let topNav = application.keyWindow?.rootViewController as? UINavigationController,
            let mapVC = topNav.viewControllers.first as? MapViewController else {
            return false
        }

        mapVC.loadView()
        restorationHandler([mapVC])
        return true
    }

}

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 Foundation.

Ownership and state

classDiagram
    AppDelegate o-- UIWindow : window
    MapViewController o-- CLLocationManager : locationManager
    MapViewController o-- MKMapView : mapView
    MapViewController o-- InitialMapRegionState : initialMapRegionState

Ownership evidence

HandoffMapViewer/HandoffMapViewerIOS/AppDelegate.swift:13 — stored dependency or nearest verified ownership anchor

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    // ...
    var window: UIWindow?
    // ...
}

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

HandoffMapViewer/HandoffMapViewerIOS/MapViewController.swift:29 — representative execution boundary

            DispatchQueue.main.async {
                for newStore in newStores {
                    self.mapView.addAnnotation(AppleStoreAnnotation(store: newStore))
                }
            }

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

HandoffMapViewer/HandoffMapViewerIOS/AppDelegate.swift:11 — representative type boundary

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    // ...
    var window: UIWindow?
    // ...
}

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

Access control

Reference code

HandoffMapViewer/HandoffMapViewerIOS/MapViewController.swift:13 — representative boundary

    private lazy var locationManager: CLLocationManager = {
        let locationManager = CLLocationManager()
        // ...
    }()

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: Controller: MapViewController, StoreDetailViewController; Delegate: AppDelegate; Store: AppleStore.
• Protocols: no local protocol declaration in the scanned source.
• Methods: application, viewDidLoad, viewDidAppear, updateUserActivityState, restoreUserActivityState, showPopoverForEditingHandoff, mapViewDidFinishLoadingMap, mapView.
• Files: HandoffMapViewer/HandoffMapViewerIOS/AppDelegate.swift, HandoffMapViewer/HandoffMapViewerMac/AppDelegate.swift, HandoffMapViewer/HandoffMapViewerIOS/MapViewController.swift, HandoffMapViewer/HandoffMapViewerIOS/StoreDetailViewController.swift, HandoffMapViewer/HandoffMapViewerMac/MapViewController.swift, HandoffMapViewer/HandoffMapViewerMac/StoreDetailViewController.swift.

Architecture takeaways

• AppDelegate is the main source-visible entry or composition anchor for this sample.
• Framework work reaches MapKit, Cocoa, UIKit, 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