iOS 13 Core Bluetooth saved peripheral services showing nil after already being discovered

Question

I am connecting to a peripheral using Core Bluetooth on iOS 13 and swift 5. I have no issues connecting or discovering services and characteristics. However, I can't seem to save the said services and characteristics for later use.

Here is my main CentralManager class that connects to the peripheral and accesses its services:

class CentralManager : NSObject{

    private var centralManager : CBCentralManager!
    var peripheralZero : CBPeripheral!
    override init(){
        super.init()

        centralManager = CBCentralManager(delegate: self, queue: nil)
    }

    func startScanning(){
        if centralManager.state == .poweredOn{
            centralManager.scanForPeripherals(withServices: nil, options: nil)
        }
    }

}

// MARK: - CBCentralManager Delegate Methods
extension CentralManager: CBCentralManagerDelegate{
    func centralManagerDidUpdateState(_ central: CBCentralManager) {
        if central.state == .poweredOn{
            print("central powered on")
        }else{
            print("Central does not support bluetooth")
        }
    }
    func centralManager(_ central: CBCentralManager, didDiscover peripheral: CBPeripheral, advertisementData: [String : Any], rssi RSSI: NSNumber){
        if(peripheral.identifier == ParticlePeripheral.DeviceUUID! as UUID){
            centralManager.stopScan()
            peripheralZero = peripheral //Here I save the found peripheral
            peripheral.delegate = self
            centralManager.connect(self.peripheralZero, options: nil)
        }
    }
    func centralManager(_ central: CBCentralManager, didConnect peripheral: CBPeripheral) {
        print("connection successful")
        peripheralZero.discoverServices(nil)
    }
}

//MARK: - CBPeripheral Delegate Methods
extension CentralManager: CBPeripheralDelegate{
    func peripheral(_ peripheral: CBPeripheral, didDiscoverServices error: Error?) {
        if let services = peripheralZero.services { // this executes to nil but if I instead use:
            // if let services = peripheral.services 
            // it works
            for service in services{
                print(service)
                peripheral.discoverCharacteristics(nil, for: service)
            }
        }

    }
}

from Apple's documentation in regards to the services property of the peripheral:

If you haven't yet called the discoverServices(_:) method to discover the services of the peripheral, or if there was an error in doing so, the value of this property is nil.

Since I have already called discoverServices shouldn't I be able to retrieve them using my peripheralZero variable? Regardless of where I try to access it in my code, the value is nil. I'm guessing the way I'm saving the peripheral is where the issue is being caused, but I really have no idea. I'm new to swift so any help would be greatly appreciated!

Answer 1

extension XXTrain: CBCentralManagerDelegate {
  func centralManagerDidUpdateState(_ central: CBCentralManager) {
    let cState = central.state
    
    switch cState {
    case .poweredOn:
      print(">>central.state is .poweredOn")
      centralManager.scanForPeripherals(withServices: services)
    @unknown default: break
    }
  }
  
  
  func centralManager(_ central: CBCentralManager, didDiscover peripheral: CBPeripheral, advertisementData: [String : Any], rssi RSSI: NSNumber) {
    discoveredPeripherals[peripheral.identifier] = peripheral
    myPeripheral = peripheral
    centralManager.connect(peripheral)
  }
  
  func centralManager(_ central: CBCentralManager, didConnect peripheral: CBPeripheral) {
    print("  -- Connected: \((peripheral.state == .connected) ? "YES" : "NO"), \(String(describing: peripheral.name)), UUID: \(peripheral.identifier)")
    
    peripheral.delegate = self
    peripheral.discoverServices(services)
  }
}


extension XXTrain: CBPeripheralDelegate {
  func peripheral(_ peripheral: CBPeripheral, didDiscoverServices error: Error?) {
    guard let services = peripheral.services else { return }
    
    for service in services {
      print("  >> Discover Services Found : \(service.uuid) service")
      peripheral.discoverCharacteristics(nil, for: service)
    }
  }

what I found was the order/placement of

peripheral.delegate = self

is important to be placed in didConnect instead of in disDiscover and

myPeripheral = peripheral

where it is "to hold a strong reference" to be placed in didDiscover