iOS Core Bluetooth: Building BLE Apps for iPhone

iOS Core Bluetooth Guide

Core Bluetooth is Apple's BLE framework for iOS, macOS, watchOS, and tvOS. It uses a delegate-based API centered on CBCentralManager (the central role) and CBPeripheralManager (the peripheral role).

CBCentralManager Setup

Always check radio state before scanning:

class BLEManager: NSObject, CBCentralManagerDelegate {
    var centralManager: CBCentralManager!

    override init() {
        super.init()
        centralManager = CBCentralManager(delegate: self,
                                          queue: .global(qos: .userInitiated))
    }

    func centralManagerDidUpdateState(_ central: CBCentralManager) {
        guard central.state == .poweredOn else { return }
        let uuid = CBUUID(string: "6E400001-B5A3-F393-E0A9-E50E24DCCA9E")
        central.scanForPeripherals(withServices: [uuid], options: nil)
    }
}

CBPeripheral and Service Discovery

Discovery is asynchronous and delegate-driven. Chain calls through delegate methods:

func centralManager(_ central: CBCentralManager, didConnect peripheral: CBPeripheral) {
    peripheral.delegate = self
    peripheral.discoverServices(nil)
}

func peripheral(_ peripheral: CBPeripheral, didDiscoverServices error: Error?) {
    peripheral.services?.forEach { peripheral.discoverCharacteristics(nil, for: $0) }
}

func peripheral(_ peripheral: CBPeripheral,
                didDiscoverCharacteristicsFor service: CBService, error: Error?) {
    service.characteristics?.forEach {
        if $0.properties.contains(.notify) { peripheral.setNotifyValue(true, for: $0) }
    }
}

Use the GATT Profile Browser to resolve UUID values to standard service names during development.

Characteristic Properties

Background Modes

<key>UIBackgroundModes</key>
<array>
    <string>bluetooth-central</string>
    <string>bluetooth-peripheral</string>
</array>

State restoration (CBCentralManagerOptionRestoreIdentifierKey) re-launches the app when the system kills it while a connection is active. Bonding is transparent — iOS stores keys in the Keychain automatically. Reconnect known devices with retrievePeripherals(withIdentifiers:) rather than scanning again.

For the Android equivalent, see Android BLE Development.