Detect whether Apple Pencil is connected to an iPad Pro

Question

Is there an API that allows you to determine whether the Apple Pencil is connected to an iPad Pro? Looking over the 9.1 SDK I don\'t see anything that directly does this. Or per

Answer 1

Took me quite a while to figure out that CBCentralManager's centralManager(_ central: CBCentralManager, didConnect peripheral: CBPeripheral) is only called when the connection is initiated via its connect(_ peripheral: CBPeripheral, options: [String : Any]? = nil) function (yes, reading the docs helps :]).

Since we have no callback for when devices have been connected to the device through the user (as is the case with Apple Pencil - I'd love to be proven wrong on this one btw), I had to resort to using a timer here.

This is how it works:

When you initialize ApplePencilReachability a timer is setup that checks for the availability of the pencil every second. If a pencil is found the timer gets invalidated, if bluetooth is turned off it also gets invalidated. When it's turned on again a new timer is created.

I am not particularly proud of it but it works :-)

import CoreBluetooth

class ApplePencilReachability: NSObject, CBCentralManagerDelegate {

  private let centralManager = CBCentralManager()
  var pencilAvailabilityDidChangeClosure: ((_ isAvailable: Bool) -> Void)?

  var timer: Timer? {
    didSet {
      if oldValue !== timer { oldValue?.invalidate() }
    }
  }

  var isPencilAvailable = false {
    didSet { 
      guard oldValue != isPencilAvailable else { return }
      pencilAvailabilityDidChangeClosure?(isPencilAvailable)
    }
  }

  override init() {
    super.init()
    centralManager.delegate = self
    centralManagerDidUpdateState(centralManager) // can be powered-on already?
  }
  deinit { timer?.invalidate() }

  func centralManagerDidUpdateState(_ central: CBCentralManager) {
    if central.state == .poweredOn {
      timer = Timer.scheduledTimer(withTimeInterval: 1, repeats: true) { 
        [weak self] timer in // break retain-cycle
        self?.checkAvailability()
        if self == nil { timer.invalidate() }
      }
    } else {
      timer = nil
      isPencilAvailable = false
    }
  }

  private func checkAvailability() {
    let peripherals = centralManager.retrieveConnectedPeripherals(withServices: [CBUUID(string: "180A")])
    let oldPencilAvailability = isPencilAvailable
    isPencilAvailable = peripherals.contains(where: { $0.name == "Apple Pencil" })
    if isPencilAvailable {
      timer = nil // only if you want to stop once detected
    }
  }

}