Implementing proximity-based interactions between a phone and watch

At a glance

Project structure

Source bundle/
├── shared/
│   ├── WatchNIDemoApp.swift
│   ├── ContentView.swift
│   ├── NearbyInteractionManager.swift
│   └── Helper.swift
├── Configuration/
│   └── SampleCode.xcconfig
├── WatchNIDemo WatchKit App/
│   └── Info.plist
├── WatchNIDemo WatchKit Extension/
│   └── Info.plist
├── WatchNIDemo.xcodeproj/
│   ├── .xcodesamplecode.plist
│   └── project.pbxproj
└── WatchNIDemo/
    └── 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 4 source declaration(s).

Overall architecture

flowchart LR
    N1["WatchNIDemoApp"]
    N2["ContentView"]
    N3["NearbyInteractionManager"]
    N4["NearbyInteraction APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

shared/WatchNIDemoApp.swift:17 — architecture anchor

@main
struct WatchNIDemoApp: App {
    // ...
    private var niManager: NearbyInteractionManager?
    // ...
}

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 Nearby Interaction.

Ownership and state

classDiagram
    WatchNIDemoApp o-- NearbyInteractionManager : niManager
    WatchNIDemoApp o-- Distance : distance
    ContentView o-- NearbyInteractionManager : niManager
    NearbyInteractionManager o-- Measurement : distance

Ownership evidence

shared/WatchNIDemoApp.swift:20 — stored dependency or nearest verified ownership anchor

@main
struct WatchNIDemoApp: App {
    // ...
    private var niManager: NearbyInteractionManager?
    // ...
}

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

shared/NearbyInteractionManager.swift:40 — representative execution boundary

class NearbyInteractionManager: NSObject, ObservableObject {
    // ...
        session?.delegateQueue = DispatchQueue.main
    // ...
}

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

shared/WatchNIDemoApp.swift:18 — representative type boundary

@main
struct WatchNIDemoApp: App {
    // ...
    private var niManager: NearbyInteractionManager?
    // ...
}

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

Access control

Reference code

shared/NearbyInteractionManager.swift:19 — representative boundary

class NearbyInteractionManager: NSObject, ObservableObject {
    // ...
    private var didSendDiscoveryToken: Bool = false
    // ...
}

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: WatchNIDemoApp; Manager: NearbyInteractionManager; View: ContentView.
• Protocols: no local protocol declaration in the scanned source.
• Methods: playHaptic, initializeNISession, deinitializeNISession, restartNISession, sendDiscoveryToken, didReceiveDiscoveryToken, sessionWasSuspended, sessionSuspensionEnded.
• Files: shared/WatchNIDemoApp.swift, shared/ContentView.swift, shared/NearbyInteractionManager.swift, shared/Helper.swift.

Architecture takeaways

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