How to prevent singleton base class getting re-initialised

TL;DR my singleton BLEManager managing Bluetooth communication keeps getting re-initialised (see console log). How should I prevent this?

Using Swift 5.9 for iOS in Xcode 15.1

My code finds multiple BT devices, and lists them for selection, also building an array of devices for reference.

Most code examples connect each device immediately. I am trying to connect later, when a specific device is selected and its View opens.

I pass the array index of the device to the individual Model to serve as a reference, hoping to pass that back to BLEManager to connect and do further communication.

After scanning has completed, the log message shows there is 1 device in it, so its not empty. As soon as I try and pass a reference back to BLEManager, the app crashes saying the array reference is out of bounds. The log shows that BLEManager is being re-initialised, presumably clearing and emptying the array.

How should I be declaring the relationship to achieve this?

Console log showing single device found:

ContentView init
  BLEManager init
didDiscover id: 39D43C90-F585-792A-5BD6-8749BA0B5385
In didDiscover devices count is 1
stopScanning
After stopScanning devices count is 1
                          <--  selection made here
DeviceModel init to device id: 0       
  BLEManager init
BLEManager connectToDevice id: 0
devices is empty
Swift/ContiguousArrayBuffer.swift:600: Fatal error: Index out of range
2023-12-28 11:45:55.149419+0000 BlueTest1[20773:1824795] Swift/ContiguousArrayBuffer.swift:600: Fatal error: Index out of range

BlueTest1App.swift

import SwiftUI

@main
struct BlueTest1App: App {
    var body: some Scene {
        WindowGroup {
            ContentView(bleManager: BLEManager())
        }
    }
}

ContentView.swift

import SwiftUI

struct TextLine: View {
    @State var dev: Device

    var body: some View {
        HStack {
            Text(dev.name).padding()
            Spacer()
            Text(String(dev.rssi)).padding()
        }
    }
}

struct PeripheralLineView: View {
    @State var devi: Device

    var body: some View {
        NavigationLink(destination: DeviceView(device: DeviceModel(listIndex: devi.id))) {
            TextLine(dev: devi)
        }
    }
}

struct ContentView: View {
    @StateObject var bleManager = BLEManager.shared

    init(bleManager: @autoclosure @escaping () -> BLEManager) {
        _bleManager = StateObject(wrappedValue: bleManager())
        print("ContentView init")
    }

    var body: some View {
        VStack (spacing: 10) {
            if !bleManager.isSwitchedOn {
                Text("Bluetooth is OFF").foregroundColor(.red)
                Text("Please enable").foregroundColor(.red)
            }
            else {
                HStack {
                    Spacer()
                    if !bleManager.isScanning {Button(action: self.bleManager.startScanning){ Text("Scan  ")
                        }
                    } else { Text("Scanning")
                    }
                }
                NavigationView {
                    List(bleManager.devices) { peripheral in
                        PeripheralLineView(devi: peripheral)
                    }.frame(height: 300)
                }
            }
        }
    }
}

//@available(iOS 15.0, *)
struct DeviceView: View {
    var device: DeviceModel
    var body: some View {
        ZStack {
            VStack {
                Text("Data Window")
                Text("Parameters")
            }
        }.onAppear(perform: {
            device.setUpModel()
        })
    }
}

BLEManager.swift

import Foundation
import CoreBluetooth

struct Device: Identifiable {
    let id: Int
    let name: String
    let rssi: Int
    let peri: CBPeripheral
}

class BLEManager: NSObject, ObservableObject, CBCentralManagerDelegate, CBPeripheralDelegate {
    static let shared: BLEManager = {
        let instance = BLEManager()
        return instance
    }()

    var BleManager = BLEManager.self
    var centralBE: CBCentralManager!
    @Published var isSwitchedOn = false
    @Published var isScanning = false
    var devices = [Device]()
    var deviceIds = [UUID]()
    private var activePeripheral: CBPeripheral!

    override init() {
        super.init()
        print("  BLEManager init")
        centralBE = CBCentralManager(delegate: self, queue: nil)
    }

    func centralManagerDidUpdateState(_ central: CBCentralManager) {
        if central.state == .poweredOn {
            isSwitchedOn = true
        }
        else { isSwitchedOn = false }
    }

    func centralManager(_ central: CBCentralManager, didDiscover peripheral: CBPeripheral, advertisementData: [String : Any], rssi RSSI: NSNumber) {
 
        if let name = advertisementData[CBAdvertisementDataLocalNameKey] as? String {
 
            if !deviceIds.contains(peripheral.identifier) {
                print("didDiscover id: \(peripheral.identifier)")
                deviceIds.append(peripheral.identifier)
                let newPeripheral = Device(id: devices.count, name: name, rssi: RSSI.intValue, peri: peripheral)
                devices.append(newPeripheral)
                print("didDiscover devices count now \(devices.count)")
            }
        }
    }

    /// save as activePeripheral and connect
    func connectToDevice(to index: Int) {
        print("BLEManager connectToDevice id: \(index)")
        if devices.isEmpty {print ("devices is empty")}
        activePeripheral = devices[index].peri
        activePeripheral.delegate = self
        centralBE.connect(activePeripheral, options: nil)
    }

    func startScanning() {
        centralBE.scanForPeripherals(withServices: nil, options: nil)
        isScanning = true
        // Stop scan after 5.0 seconds
        let _: Timer = Timer.scheduledTimer(timeInterval: 5.0, target: self, selector: #selector(stopScanning), userInfo: nil, repeats: false)
    }
    @objc func stopScanning() {   // need @objc for above Timer selector
        print("stopScanning")
        centralBE.stopScan()
        isScanning = false
        print("After stopScanning devices count is \(devices.count)")
    }

    func peripheral(_ peripheral: CBPeripheral, didDiscoverCharacteristicsFor service: CBService, error: Error?) { }

    func disconnect(peripheral: Int) { }

    func discoverServices(peripheral: CBPeripheral) { }

    func discoverCharacteristics(peripheral: CBPeripheral) { }

    func peripheral(_ peripheral: CBPeripheral, didDiscoverServices error: Error?) { }

    func peripheral(_ peripheral: CBPeripheral, didUpdateValueFor characteristic: CBCharacteristic, error: Error?) { }
}

DeviceModel.swift

import Foundation
import CoreBluetooth

class DeviceModel: BLEManager {
    var index: Int   //CBPeripheral position in found array

    init(listIndex: Int) {
        index = listIndex
        print("DeviceModel init to device id: \(index)")
   }

    func setUpModel() {
        connectToDevice(to: index)
    }

}