为什么没有调用发现外围设备？

Question

我想扫描附近的所有蓝牙设备。 我不知道我在代码中做错了什么，所以我的 didDiscover 外围方法没有被调用。 下面是我尝试过的代码。

import UIKit
import CoreBluetooth

class HomeViewController: UIViewController {

var centralManager: CBCentralManager?
var peripherals = Array<CBPeripheral>()

override func viewDidLoad() {
    super.viewDidLoad()

    //Initialise CoreBluetooth Central Manager
    centralManager = CBCentralManager(delegate: self, queue: nil)
}
}
extension HomeViewController: CBCentralManagerDelegate {
func centralManagerDidUpdateState(_ central: CBCentralManager) {
    if (central.state == .poweredOn){
        self.centralManager?.scanForPeripherals(withServices: nil, options: nil)
    }
    else {
        // do something like alert the user that ble is not on
        let alert = UIAlertController(title: "Bluetooth is off", message: "Please turn on your bluetooth", preferredStyle: .alert)
        alert.addAction(UIAlertAction(title: "Ok", style: .default, handler: nil))
        self.present(alert, animated: true, completion: nil)
    }
}

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

    print(peripheral)

}
}

请帮忙。