实例成员不能在Xcode 9中的类型'ViewController'上使用

Question

我一直在尝试使用Swift在Xcode 9中创建一个应用程序，而我正试图在电池电量变化时刷新标签显示。

但每次我使用“label.text = value”时都会收到错误消息，指出实例成员'LineTwo'不能用于'ViewController'类型。

我不确定为什么我会收到此错误。

这是我的完整代码。

import UIKit

class ViewController: UIViewController {

@IBOutlet weak var LineTwo: UILabel!

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.
    UIDevice.current.isBatteryMonitoringEnabled = true
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
    // Dispose of any resources that can be recreated.
}

let observer = NotificationCenter.default.addObserver(
    forName: NSNotification.Name.UIDeviceBatteryLevelDidChange,
    object: nil, queue: nil) {_ in

        let msgOne = String(Int(UIDevice.current.batteryLevel*100))+"% ,Battery changed!"
        print(msgOne)
        LineTwo.text = msgOne //error:Instance member 'LineTwo' cannot be used on type 'ViewController'
        }
}