NotificationCenter在Swift 3.1中返回batteryLevel和batteryState的正確語法是什么

Question

我是Swift的新手（使用Xcode 8.3.3，Swift 3.1），並且我試圖顯示電池電量和電池狀態並在值更改時更新它們。 這是我到目前為止的內容：

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"
        }
    }    
}

當級別或狀態更改生成此錯誤消息時，我的應用程序崩潰：[Battery_Display.ViewController batteryLevelDidChange：]：無法識別的選擇器發送到實例0x100b0cf10'。

我究竟做錯了什么？

Answer 1

基本上，您錯於通知處理程序的位置。 這些處理程序在viewDidLoad方法中聲明，並且不在NotificationCenter單例的范圍內。 只需將它們從viewDidLoad取出，它應該可以工作：

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"
        }
    }
}