即使在按下主页按钮时我处于后台，我也想继续计时。我该怎么做？

这是我的工作代码，它是锻炼的计时器。计数完成后我正在使用闹钟:

import UIKit
import AVFoundation
class ViewController: UIViewController, UIPickerViewDelegate, UIPickerViewDataSource {

var pickerInfo: [String] = []
var tempsCuisson:Int = 0
var timer:Timer = Timer()
var lecteur:AVAudioPlayer = AVAudioPlayer()
var estActif:Bool = false
var selection:Int?

//outlets
@IBOutlet weak var minuteurLabel: UILabel!

override func viewDidAppear(_ animated: Bool) {
    minuteurLabel.text = minuteurString(temps: tempsCuisson)
}
@IBOutlet weak var activerMinuteurBtn: UIButton!



@IBOutlet weak var pickerView: UIPickerView!
@IBOutlet weak var navBar: UINavigationBar!


//actions
@IBAction func activerMinuteurAction(_ sender: UIButton) {

    compteur()
}

@IBAction func resetMinuteurAction(_ sender: UIButton) {
    resetCompteur()
}



override func viewDidLoad() {
    super.viewDidLoad()

    //datasource + delegate
    pickerView.dataSource = self
    pickerView.delegate = self

    pickerInfo = ["00.15", "00.30", "00:45",
                  "01:00", "01:15", "01:30", "01:45",
                  "02:00", "02:15", "02:30", "02:45",
                  "03:00", "03:15", "03:30", "03:45",
                  "04:00", "04:15", "04:30", "04:45",
                  "05:00", "05:15", "05:30", "05:45",
                  "06:00", "06:15", "06:30", "06:45",
                  "07:00", "07:15", "07:30", "07:45",
                  "08:00", "08:15", "08:30", "08:45",
                  "09:00", "09:15", "09:30", "09:45", "10:00"
    ]

    activerMinuteurBtn.setTitleColor(UIColor.white, for: UIControlState.normal)

    activerMinuteurBtn.isEnabled = false
    activerMinuteurBtn.alpha = 0.3

    alarm()
}



func selectionCuisson(selection: Int) {

    var titreVC:String?

    switch selection {
    case 0:
        //code
        tempsCuisson = 015
        minuteurLabel.text = minuteurString(temps: tempsCuisson)
        navBar.topItem?.title = titre(str: pickerInfo[selection])
        break

    case 1:
        //code
        tempsCuisson = 030
        minuteurLabel.text = minuteurString(temps: tempsCuisson)
        navBar.topItem?.title  = titre(str: pickerInfo[selection])
        break


    case 2:
        //code
        tempsCuisson = 045
        minuteurLabel.text = minuteurString(temps: tempsCuisson)
        navBar.topItem?.title  = titre(str: pickerInfo[selection])
        break

    case 3:
        //code
        tempsCuisson = 060
        minuteurLabel.text = minuteurString(temps: tempsCuisson)
        navBar.topItem?.title  = titre(str: pickerInfo[selection])
        break

all cases...

    default:
        //code
        print("Aucune sélection")
        break

    }

    //pour afficher option sélectionnée dans barre navigation
    //self.title = titreVC

    activerMinuteurBtn.isEnabled = true
    activerMinuteurBtn.alpha = 1
    minuteurLabel.textColor = UIColor.black

}

func minuteurString(temps: Int) -> String {
    let minutes = Int(temps) / 60 % 60
    let secondes = Int(temps) % 60

    return String(format: "%02i:%02i", minutes, secondes)
}

func compteur() {

    if (!estActif) {

        timer = Timer.scheduledTimer(timeInterval: 1, target: self, selector: #selector(ViewController.incrementer), userInfo: nil, repeats: true)
        timer.fire()
        activerMinuteurBtn.setTitle("STOP", for: UIControlState.normal)
        activerMinuteurBtn.setTitleColor(UIColor.orange, for: UIControlState.normal)
        estActif = true

    } else {

        timer.invalidate()
        activerMinuteurBtn.setTitle("Démarrer", for: UIControlState.normal)
        activerMinuteurBtn.setTitleColor(UIColor.blue, for: UIControlState.normal)
        estActif = false

    }


}

func incrementer() {

    if (tempsCuisson == 0) {

        timer.invalidate()
        minuteurLabel.text = "00:00"
        activerMinuteurBtn.setTitle("Démarrer", for: UIControlState.normal)
        activerMinuteurBtn.setTitleColor(UIColor.blue, for: UIControlState.normal)

        minuteurLabel.textColor = UIColor.green

        activerMinuteurBtn.isEnabled = false
        activerMinuteurBtn.alpha = 0.3

        lecteur.play()

    } else {
        tempsCuisson -= 1
        minuteurLabel.text = minuteurString(temps: tempsCuisson)
    }

}

func resetCompteur() {
    timer.invalidate()
    tempsCuisson = 0
    minuteurLabel.text = "00:00"
    activerMinuteurBtn.setTitle("Démarrer", for: UIControlState.normal)
    activerMinuteurBtn.setTitleColor(UIColor.white, for: UIControlState.normal)

    estActif = false

    activerMinuteurBtn.isEnabled = false
    activerMinuteurBtn.alpha = 0.3

    pickerView.selectRow(0, inComponent: 0, animated: true)

}

//AVAudioPlayer

func alarm() {
   DispatchQueue.global(qos: .userInitiated).async {
    let fichier = Bundle.main.path(forResource: "alarm", ofType: "mp3")

    do {
        try AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryAmbient, with:[.duckOthers])
        try AVAudioSession.sharedInstance().setActive(true)
        try self.lecteur = AVAudioPlayer(contentsOf: (URL(string: fichier!))!)
    } catch {
        print("erreur lecture ficher MP3")
        }
    }
}

//Retourner Titre

func titre(str:String) -> String {
    return str
}

//MARK - PickerViewDataSource

// returns the number of 'columns' to display.
func numberOfComponents(in pickerView: UIPickerView) -> Int {
    return 1
}


// returns the # of rows in each component..
func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
    return pickerInfo.count
}

func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {

    return pickerInfo[row]

}

//changer couleur pickerView label
func pickerView(_ pickerView: UIPickerView, viewForRow row: Int, forComponent component: Int, reusing view: UIView?) -> UIView {
    let label = UILabel(frame: CGRect(x: 0, y: 0, width: pickerView.frame.size.width, height: 44))
    label.textColor = UIColor.white
    label.font = UIFont(name: "HelveticaNeue-Bold", size: 22)
    label.textAlignment = .center
    label.text = String(format:" %@", pickerInfo[row])

    if (row == selection) {
        label.textColor = UIColor.yellow
    }

    return label
}
//MARK - PickerViewDelegate
func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {

    selectionCuisson(selection: row)
    selection = row
}
}

最佳答案

好吧，无需深入研究您的代码，您似乎正在使用 Timer.scheduledTimer 每秒手动递减用户设置的时间。

正如您所发现的那样，这不是一项好技术 - 只有当您知道您可以绝对控制应用程序的时间时，它才有效。

相反，您应该做的是存储用户启动警报的时间、预计的结束时间，并运行计时器以定期更新 UI。

(我的代码在这里并不完美，但它应该为您指明正确的方向，以解决让计时器在后台运行的问题。)

例如

class ViewController: UIViewController {
    // this is pseudo-code as I don't have my compiler open :(
    let start: Date!
    let end: Date!

    func selectionCuisson(selection: Int) {

         ...

         start = Date()
         end = Date(timeInterval: tempsCuisson, since: start)
    }

 }

然后您创建一个计时器，它只会更新 UI。

// You can set this to be faster than the increment, for a smoother UI experience
// put in compteur()? I think
timer = Timer.scheduledTimer(timeInterval: 0.2, target: self, selector: #selector(ViewController.incrementer), userInfo: nil, repeats: true)
timer.fire()

...

func incrementer() {
    let tempsCuisson = end - start
    if tempsCuisson < 0 {
        // End your Timing Function here
        timer.invalidate()
        ...
        lecteur.play()
    } else {
        minuteurLabel.text = minuteurString(temps: tempsCuisson)
    }
}

您还可以使用 end 日期将本地通知设置为在应用程序进入后台时关闭

// when the app becomes inactive
let notification = UILocalNotification()
...
notification.fireDate = end
UIApplication.shared.scheduleLocalNotification(notification)

关于ios - Swift 3 - 如何让我的计时器在后台计数？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/43330907/