Implementing interactions between users in close proximity

At a glance

Project structure

Source bundle/
├── NIPeekaboo/
│   ├── AppDelegate.swift
│   ├── MultipeerConnectivitySupport/
│   │   └── MPCSession.swift
│   ├── ViewController.swift
│   ├── SceneDelegate.swift
│   ├── MathUtilities.swift
│   ├── Base.lproj/
│   │   ├── LaunchScreen.storyboard
│   │   └── Main.storyboard
│   └── Info.plist
├── Configuration/
│   └── SampleCode.xcconfig
└── NIPeekaboo.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 6 project/configuration file(s) and 6 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["ViewController"]
    N3["MPCSession"]
    N4["NearbyInteraction APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

NIPeekaboo/AppDelegate.swift:10 — architecture anchor

@main
class AppDelegate: UIResponder, UIApplicationDelegate {
    // ...
    func application(_ application: UIApplication, didFinishLaunchingWithOptions
                     launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        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 Nearby Interaction.

Ownership and state

classDiagram
    MPCSessionConstants *-- String : kKeyIdentity
    MPCSession o-- Callback : peerDataHandler
    MPCSession o-- Callback : peerConnectedHandler
    MPCSession o-- Callback : peerDisconnectedHandler

Ownership evidence

NIPeekaboo/MultipeerConnectivitySupport/MPCSession.swift:12 — stored dependency or nearest verified ownership anchor

struct MPCSessionConstants {
    static let kKeyIdentity: String = "identity"
}

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

NIPeekaboo/MultipeerConnectivitySupport/MPCSession.swift:78 — representative execution boundary

            DispatchQueue.main.async {
                handler(peerID)
            }

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

NIPeekaboo/AppDelegate.swift:11 — representative type boundary

@main
class AppDelegate: UIResponder, UIApplicationDelegate {
    // ...
        return true
    // ...
}

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

Access control

Reference code

NIPeekaboo/MultipeerConnectivitySupport/MPCSession.swift:19 — representative boundary

class MPCSession: NSObject, MCSessionDelegate, MCNearbyServiceBrowserDelegate, MCNearbyServiceAdvertiserDelegate {
    // ...
    private let serviceString: String
    // ...
}

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: ViewController; Delegate: AppDelegate, SceneDelegate; Session: MPCSession.
• Protocols: no local protocol declaration in the scanned source.
• Methods: application, start, suspend, invalidate, sendDataToAllPeers, sendData, peerConnected, peerDisconnected.
• Files: NIPeekaboo/AppDelegate.swift, NIPeekaboo/MultipeerConnectivitySupport/MPCSession.swift, NIPeekaboo/ViewController.swift, NIPeekaboo/SceneDelegate.swift.

Architecture takeaways

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