獲取電池狀態和電池電量

override func viewDidLoad() {
    super.viewDidLoad()
    NotificationCenter.default.addObserver(self, selector: Selector(("batteryStateDidChange:")), name: NSNotification.Name.UIDeviceBatteryStateDidChange, object: nil)
    NotificationCenter.default.addObserver(self, selector: Selector(("batteryLevelDidChange:")), name: NSNotification.Name.UIDeviceBatteryLevelDidChange, object: nil)

    // Stuff...
}

func batteryStateDidChange(notification: NSNotification){
    // The stage did change: plugged, unplugged, full charge...
}

func batteryLevelDidChange(notification: NSNotification){
    
    let batteryLevel = UIDevice.current.batteryLevel
    if batteryLevel < 0.0 {
        print(" -1.0 means battery state is UIDeviceBatteryStateUnknown")
        return
    }
    
    print("Battery Level : \(batteryLevel * 100)%")
    // The battery's level did change (98%, 99%, ...)
}