Scanning for Peripherals

Once the CBCentralManager is up and powered on, you can create a function that scan for peripherals around us.

Create a function called startScanning. Call the method scanForPeripherals(withServices:).

This method scans for peripherals that are advertising services. Now since the unique identifier is set up, add that reference to the method.

func startScanning() -> Void {
  // Start Scanning
  centralManager?.scanForPeripherals(withServices: [CBUUIDs.BLEService_UUID])

Now add the startScanning() function to the centralManagerDidUpdateState to scan as soon as the app opens.

extension ViewController: CBCentralManagerDelegate {

  func centralManagerDidUpdateState(_ central: CBCentralManager) {
     switch central.state {
          case .poweredOff:
              print("Is Powered Off.")
          case .poweredOn:
              print("Is Powered On.")
          case .unsupported:
              print("Is Unsupported.")
          case .unauthorized:
          print("Is Unauthorized.")
          case .unknown:
          case .resetting:
          @unknown default:


When you run your app, your device will start scanning for peripherals.

Discovering Peripherals

Now that scanning is started, what happens when a peripheral is discovered?

Every time a peripheral is discovered, the CBCentralManager will notify you by calling the centralManager(_:didDiscover:advertisementData:rssi:) function on its delegate.

This function provides the following information about the newly discovered peripheral:

  • The discovered peripheral is recognized and can be stored as a CBPeripheral.
  • The discovered peripheral has stored advertisement data.
  • The current received signal strength indicator (RSSI) of the peripheral, in decibels.

Since you are interested in connecting to one peripheral, create an instance of a peripheral.

private var bluefruitPeripheral: CBPeripheral!

Call the didDiscover function. This tells the delegate the central manager discovered a peripheral while scanning for devices.

func centralManager(_ central: CBCentralManager, didDiscover peripheral: CBPeripheral,advertisementData: [String : Any], rssi RSSI: NSNumber) {

    bluefruitPeripheral = peripheral

    bluefruitPeripheral.delegate = self

    print("Peripheral Discovered: \(peripheral)")
  	print("Peripheral name: \(")
    print ("Advertisement Data : \(advertisementData)")

The implementation of this function performs the following actions:

  • Set the bluefruitPeripheral variable to the new peripheral found.
  • Set the peripheral's delegate to self (ViewController)
  • Printed the newly discovered peripheral's information in the console.
  • Stopped scanning for peripherals.

Next up - actually connect to that peripheral.

This guide was first published on Jul 27, 2017. It was last updated on 2021-02-23 12:51:57 -0500.

This page (Scanning for Peripherals) was last updated on Dec 04, 2021.

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