ios - NotificationCenter 在 Swift 3.1 中返回 batteryLevel 和 batteryState 的正确语法是什么

Question

我是 Swift 的新手(使用 Xcode 8.3.3、Swift 3.1)，我正在尝试显示电池电量和电池状态并在值更改时更新它们。这是我到目前为止所拥有的:

import UIKit
class ViewController: UIViewController {

@IBOutlet weak var myBatteryPercent: UILabel!
@IBOutlet weak var myBatteryState: UILabel!

override func viewDidLoad() {
    super.viewDidLoad()

    UIDevice.current.isBatteryMonitoringEnabled = true


    NotificationCenter.default.addObserver(self, selector: Selector(("batteryLevelDidChange:")),
     name: NSNotification.Name.UIDeviceBatteryLevelDidChange,
     object: nil)

    NotificationCenter.default.addObserver(self, selector: Selector(("batteryStateDidChange:")),
     name: NSNotification.Name.UIDeviceBatteryStateDidChange,
     object: nil)

    var batteryLevel: Float {
        return UIDevice.current.batteryLevel
    }

    var batteryState: UIDeviceBatteryState {
        return UIDevice.current.batteryState
    }

    switch batteryState {
    case .unplugged, .unknown:
        myBatteryState.text = "not charging"
    case .charging, .full:
        myBatteryState.text = "charging or full"
    }

    myBatteryPercent.text = "\(Int((batteryLevel) * 100))%"



    func batteryLevelDidChange (notification: Notification) {
        myBatteryPercent.text = "\(Int((batteryLevel) * 100))%"
    }
    func batteryStateDidChange (notification: Notification) {
        switch batteryState {
        case .unplugged, .unknown:
            myBatteryState.text = "not charging"
        case .charging, .full:
            myBatteryState.text = "charging or full"
        }
    }    
}

当级别或状态发生变化时，我的应用程序崩溃并生成此错误消息:[Battery_Display.ViewController batteryLevelDidChange:]: unrecognized selector sent to instance 0x100b0cf10'。

我做错了什么？

Answer 1

基本上您对通知处理程序的放置是错误的。处理程序在 viewDidLoad 方法内声明，它们超出了 NotificationCenter 单例的范围。只需将它们从 viewDidLoad 中取出，它就可以工作了:

import UIKit
class ViewController: UIViewController {

    @IBOutlet weak var myBatteryPercent: UILabel!
    @IBOutlet weak var myBatteryState: UILabel!
    var batteryLevel: Float {
        return UIDevice.current.batteryLevel
    }

    var batteryState: UIDeviceBatteryState {
        return UIDevice.current.batteryState
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        UIDevice.current.isBatteryMonitoringEnabled = true


        NotificationCenter.default.addObserver(self, selector: #selector(batteryLevelDidChange), name: NSNotification.Name.UIDeviceBatteryLevelDidChange, object: nil)

        NotificationCenter.default.addObserver(self, selector: #selector(batteryStateDidChange), name: NSNotification.Name.UIDeviceBatteryStateDidChange, object: nil)

        switch batteryState {
        case .unplugged, .unknown:
            myBatteryState.text = "not charging"
        case .charging, .full:
            myBatteryState.text = "charging or full"
        }

        myBatteryPercent.text = "\(Int((batteryLevel) * 100))%"

    }

    func batteryLevelDidChange (notification: Notification) {
        myBatteryPercent.text = "\(Int((batteryLevel) * 100))%"
    }

    func batteryStateDidChange (notification: Notification) {
        switch batteryState {
        case .unplugged, .unknown:
            myBatteryState.text = "not charging"
        case .charging, .full:
            myBatteryState.text = "charging or full"
        }
    }
}