在Swift 3.1中，NotificationCenter返回batteryLevel和batteryState的正确语法是什么

import UIKit

let notificationCenter = NotificationCenter.default

// 监听电池状态变化
notificationCenter.addObserver(forName: UIDevice.batteryLevelDidChangeNotification, object: nil, queue: nil) { notification in
    let batteryLevel = UIDevice.current.batteryLevel
    print("Battery Level: \(batteryLevel)")
}

// 监听电池电量变化
notificationCenter.addObserver(forName: UIDevice.batteryStateDidChangeNotification, object: nil, queue: nil) { notification in
    let batteryState = UIDevice.current.batteryState
    print("Battery State: \(batteryState.rawValue)")
}