Transferring Data Between Bluetooth Low Energy Devices

At a glance

Project structure

Source bundle/
├── CoreBluetoothLESample/
│   ├── AppDelegate.swift
│   ├── CentralViewController.swift
│   ├── PeripheralViewController.swift
│   ├── TransferService.swift
│   ├── Base.lproj/
│   │   ├── LaunchScreen.storyboard
│   │   └── Main.storyboard
│   └── Info.plist
├── Configuration/
│   └── SampleCode.xcconfig
└── CoreBluetoothLESample.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 4 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["CentralViewController"]
    N3["TransferService"]
    N4["CoreBluetooth APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

CoreBluetoothLESample/AppDelegate.swift:11 — architecture anchor

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.

        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 Core Bluetooth.

Ownership and state

classDiagram
    AppDelegate o-- UIWindow : window
    CentralViewController o-- UITextView : textView
    CentralViewController o-- CBCentralManager : centralManager
    CentralViewController o-- CBPeripheral : discoveredPeripheral

Ownership evidence

CoreBluetoothLESample/AppDelegate.swift:14 — 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

CoreBluetoothLESample/CentralViewController.swift:338 — representative execution boundary

            DispatchQueue.main.async() {
                self.textView.text = String(data: self.data, encoding: .utf8)
            }

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

CoreBluetoothLESample/AppDelegate.swift:12 — 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

CoreBluetoothLESample/CentralViewController.swift:52 — representative boundary

    private func retrievePeripheral() {
        // ...
        let connectedPeripherals: [CBPeripheral] = (centralManager.retrieveConnectedPeripherals(withServices: [TransferService.serviceUUID]))
        // ...
    }

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

Receiving text is a callback chain across central discovery, peripheral service discovery, characteristic subscription, and repeated value notifications.

sequenceDiagram
    participant Central as CBCentralManager
    participant Controller as CentralViewController
    participant Peripheral as CBPeripheral
    participant UI as UITextView
    Central-->>Controller: didDiscover(peripheral, RSSI)
    Controller->>Central: connect(peripheral)
    Central-->>Controller: didConnect(peripheral)
    Controller->>Peripheral: discoverServices(transfer UUID)
    Peripheral-->>Controller: didDiscoverServices
    loop each discovered service
        Controller->>Peripheral: discoverCharacteristics(transfer UUID)
    end
    Peripheral-->>Controller: didDiscoverCharacteristicsFor
    Controller->>Peripheral: setNotifyValue(true)
    loop characteristic notifications
        Peripheral-->>Controller: didUpdateValueFor
        Controller->>Controller: Append bytes until EOM
    end
    Controller-->>UI: Display assembled text on main queue

Reference code

CoreBluetoothLESample/CentralViewController.swift:223 — centralManager

    func centralManager(_ central: CBCentralManager, didConnect peripheral: CBPeripheral) {
        os_log("Peripheral Connected")

        // Stop scanning
        centralManager.stopScan()
        os_log("Scanning stopped")

        // set iteration info
        connectionIterationsComplete += 1
        writeIterationsComplete = 0

        // Clear the data that we may already have
        data.removeAll(keepingCapacity: false)

        // Make sure we get the discovery callbacks
        peripheral.delegate = self

        // Search only for services that match our UUID
        peripheral.discoverServices([TransferService.serviceUUID])
    }

CoreBluetoothLESample/CentralViewController.swift:278 — peripheral

    func peripheral(_ peripheral: CBPeripheral, didDiscoverServices error: Error?) {
        if let error = error {
            os_log("Error discovering services: %s", error.localizedDescription)
            cleanup()
            return
        }

        // Discover the characteristic we want...

        // Loop through the newly filled peripheral.services array, just in case there's more than one.
        guard let peripheralServices = peripheral.services else { return }
        for service in peripheralServices {
            peripheral.discoverCharacteristics([TransferService.characteristicUUID], for: service)
        }
    }

Naming conventions

• Types: Controller: CentralViewController, PeripheralViewController; Delegate: AppDelegate; Service: TransferService.
• Protocols: no local protocol declaration in the scanned source.
• Methods: application, viewDidLoad, viewWillDisappear, retrievePeripheral, cleanup, writeData, centralManagerDidUpdateState, centralManager.
• Files: CoreBluetoothLESample/AppDelegate.swift, CoreBluetoothLESample/CentralViewController.swift, CoreBluetoothLESample/PeripheralViewController.swift, CoreBluetoothLESample/TransferService.swift.

Architecture takeaways

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