Interacting with Bluetooth peripherals during background app refresh

At a glance

Project structure

Source bundle/
├── BARBluetooth WatchKit Extension/
│   ├── BARBluetoothApp.swift
│   ├── ComplicationController.swift
│   ├── ExtensionDelegate.swift
│   ├── NotificationHandler.swift
│   ├── RootView.swift
│   ├── BluetoothReceiver.swift
│   └── Info.plist
├── BARBluetooth/
│   ├── SamplePeripheralApp.swift
│   ├── ApplicationDelegate.swift
│   ├── RootView.swift
│   └── BluetoothSender.swift
└── shared/
    └── BluetoothConstants.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 5 project/configuration file(s) and 14 source declaration(s).

Overall architecture

flowchart LR
    Bundle["Sample bundle"]
    V1["BARBluetooth WatchKit Extension"]
    V2["BARBluetooth"]
    Boundary["CoreBluetooth / SwiftUI APIs"]
    Bundle --> V1
    V1 --> Boundary
    Bundle --> V2
    V2 --> Boundary

Reference code

BARBluetooth WatchKit Extension/BARBluetoothApp.swift:10 — architecture anchor

@main
struct BARBluetoothApp: App {
    // ...
}

Interpretation

The branches represent separate entry-bearing project variants in the downloaded bundle, not runtime calls between those variants. Each branch is intentionally collapsed at the documented framework boundary; the detailed target-local flow remains in the cited files. Ownership is claimed only where the next section cites a stored property or assignment.

Ownership and state

classDiagram
    BARBluetoothApp *-- String : name
    BARBluetoothApp o-- ExtensionDelegate : delegate
    SamplePeripheralApp *-- String : name
    SamplePeripheralApp o-- ApplicationDelegate : delegate

Ownership evidence

BARBluetooth WatchKit Extension/BARBluetoothApp.swift:13 — stored dependency or nearest verified ownership anchor

@main
struct BARBluetoothApp: App {
    // ...
    static let name: String = "BARBluetooth"
    
    // ...
}

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.

Class and protocol design

BARBluetooth WatchKit Extension/BluetoothReceiver.swift:11 — representative type boundary

protocol BluetoothReceiverDelegate: AnyObject {
    func didReceiveData(_ message: Data) -> Int
    func didCompleteDisconnection(from peripheral: CBPeripheral, mustDisconnect: Bool)
    func didFailWithError(_ error: BluetoothReceiverError)
}

The source explicitly defines local protocol relationships: ExtensionDelegate → BluetoothReceiverDelegate, ApplicationDelegate → BluetoothSenderDelegate.

Access control

Reference code

BARBluetooth WatchKit Extension/BluetoothReceiver.swift:28 — representative boundary

    private var logger = Logger(
        subsystem: BARBluetoothApp.name,
        category: String(describing: BluetoothReceiver.self)
    )
    
    var notificationHandler = ExtensionDelegate.instance.notificationHandler

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: BARBluetoothApp, SamplePeripheralApp; Controller: ComplicationController; Delegate: ApplicationDelegate, BluetoothReceiverDelegate, BluetoothSenderDelegate, ExtensionDelegate; Handler: NotificationHandler; View: RootView.
• Protocols: BluetoothReceiverDelegate, BluetoothSenderDelegate.
• Methods: getDataFor, updateAllActiveComplications, getComplicationDescriptors, handleSharedComplicationDescriptors, getTimelineEndDate, getPrivacyBehavior, getCurrentTimelineEntry, getTimelineEntries.
• Files: BARBluetooth WatchKit Extension/BARBluetoothApp.swift, BARBluetooth/SamplePeripheralApp.swift, BARBluetooth/ApplicationDelegate.swift, BARBluetooth/RootView.swift, BARBluetooth WatchKit Extension/ComplicationController.swift, BARBluetooth WatchKit Extension/ExtensionDelegate.swift.

Architecture takeaways

• BARBluetoothApp is the main source-visible entry or composition anchor for this sample.
• Framework work reaches CoreBluetooth, SwiftUI, UserNotifications, ClockKit 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.
• Local protocol relationships provide an explicit substitution boundary.

Source map

• Official Apple documentation