在手机休眠时运行计时器

Question

我正在构建一个应用程序，如果用户将屏幕发送到后台，或者如果他们让手机进入睡眠状态并再次打开它，我需要一个计时器来运行。我需要计时器继续运行。

我尝试记录退出并再次输入的时间，减去两者并将其添加到运行计数中，它似乎在 Xcode 模拟器上运行良好，但当我在手机上运行它时却没有工作。有任何想法吗？

这是供参考的代码。
计时器从一个按钮开始，我没有包含该部分，但它只是一个调用 timer.fire() 函数的简单 IBAction。

var time = 0.0
var timer = Timer()
var exitTime : Double = 0
var resumeTime : Double = 0

override func viewWillDisappear(_ animated: Bool) {
    super.viewWillDisappear(true)
    exitTime = Date().timeIntervalSinceNow
}

override func awakeFromNib() {
    super.awakeFromNib()
    resumeTime = Date().timeIntervalSinceNow
    time += (resumeTime-exitTime)
    timer.fire()
}


func startTimer() {
    if !isTimeRunning {
        timer = Timer.scheduledTimer(timeInterval: 0.1, target: self, selector: 
        #selector(WorkoutStartedViewController.action), userInfo: nil, repeats: true)
        isTimeRunning = true
    }
}

func pauseTimer() {
    timer.invalidate()
    isTimeRunning = false
}

@objc func action()
{
    time += 0.1
    timerLabel.text = String(time)
    let floorCounter = Int(floor(time))
    let hour = floorCounter/3600
    let minute = (floorCounter % 3600)/60
    var minuteString = "\(minute)"
    if minute < 10 {
        minuteString = "0\(minute)"
    }

    let second = (floorCounter % 3600) % 60
    var secondString = "\(second)"
    if second < 10 {
        secondString = "0\(second)"
    }

    if time < 3600.0 {
        timerLabel.text = "\(minuteString):\(secondString)"
    } else {
        timerLabel.text = "\(hour):\(minuteString):\(secondString)"
    }

}

Answer 1

您确实有正确的想法，但我看到的第一个问题是 viewWillDissapear 仅在您离开视图控制器以转到新的视图控制器时调用 - 当应用程序离开视图进入后台时不会调用它（主页按钮按下）

我相信您正在寻找的回调函数是UIApplication.willResignActive（进入后台）和UIApplication.didBecomeActive（应用重新打开）

您可以在AppDelegate 中访问这些方法，或者您可以在视图控制器上设置它们，在这里混合您的代码和一些更改以在一个初始 VC 上生成一个工作示例：

import UIKit
import CoreData

class ViewController: UIViewController {

    @IBOutlet weak var timerLabel: UILabel!

    var time = 0.0
    var timer = Timer()
    var exitTime : Date?    // Change to Date
    var resumeTime : Date?    // Change to Date
    var isTimeRunning = false

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        startTimer()
    }

    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        NotificationCenter.default.addObserver(self,
        selector: #selector(applicationDidBecomeActive),
        name: UIApplication.didBecomeActiveNotification,
        object: nil)
        // Add willResign observer
        NotificationCenter.default.addObserver(self,
        selector: #selector(applicationWillResign),
        name: UIApplication.willResignActiveNotification,
        object: nil)
    }

    override func viewWillDisappear(_ animated: Bool) {
        // Remove becomeActive observer
        NotificationCenter.default.removeObserver(self,
                                                  name: UIApplication.didBecomeActiveNotification,
                                                  object: nil)
        // Remove becomeActive observer
        NotificationCenter.default.removeObserver(self,
                                                  name: UIApplication.willResignActiveNotification,
                                                  object: nil)

    }

    func startTimer() {
        if !isTimeRunning {
            timer = Timer.scheduledTimer(timeInterval: 0.1, target: self, selector:
                #selector(self.action), userInfo: nil, repeats: true)
            isTimeRunning = true
        }
    }

    @objc func action() {
        time += 0.1
        timerLabel.text = String(time)
        let floorCounter = Int(floor(time))
        let hour = floorCounter/3600
        let minute = (floorCounter % 3600)/60
        var minuteString = "\(minute)"
        if minute < 10 {
            minuteString = "0\(minute)"
        }

        let second = (floorCounter % 3600) % 60
        var secondString = "\(second)"
        if second < 10 {
            secondString = "0\(second)"
        }

        if time < 3600.0 {
            timerLabel.text = "\(minuteString):\(secondString)"
        } else {
            timerLabel.text = "\(hour):\(minuteString):\(secondString)"
        }
    }

    @objc func applicationDidBecomeActive() {
        // handle event
        lookForActiveTimers()
    }

    func lookForActiveTimers() {

        var timers = [NSManagedObject]()

        guard let appDelegate = UIApplication.shared.delegate as? AppDelegate else {
            return
        }
        let managedContext = appDelegate.persistentContainer.viewContext
        let fetchRequest = NSFetchRequest<NSManagedObject>(entityName: "Timers")

        //3
        do {
            timers = try managedContext.fetch(fetchRequest)
            print("timers: \(timers)")

            var activeTimer: NSManagedObject?

            for timer in timers {
                if let active = timer.value(forKey: "active") as? Bool {
                    if active {
                        activeTimer = timer
                    }
                }
            }

            if let activeTimer = activeTimer {

                // Handle active timer (may need to go to a new view)
                if let closeDate = activeTimer.value(forKey: "appCloseTime") as? Date {

                    if let alreadyTimed = activeTimer.value(forKey: "alreadyTimed") as? Double {

                        let now = Date()
                        let difference = now.timeIntervalSince(closeDate)

                        // Handle set up again here
                        print("App opened with a difference of \(difference) and already ran for a total of \(alreadyTimed) seconds before close")

                        time = alreadyTimed + difference
                        startTimer()

                    }
                }

            } else {
                print("We dont have any active timers")
            }

            // Remove active timers because we reset them up
            for timer in timers {
                managedContext.delete(timer)
            }
            do {
                print("deleted")
                try managedContext.save() // <- remember to put this :)
            } catch {
                // Do something... fatalerror
            }

        } catch let error as NSError {
          print("Could not fetch. \(error), \(error.userInfo)")
        }
    }

    @objc func applicationWillResign() {
        // handle event
        saveActiveTimer()
    }


    func saveActiveTimer() {
        if isTimeRunning {
            // Create a new alarm object
            guard let appDelegate =
              UIApplication.shared.delegate as? AppDelegate else {
              return
            }

            let context = appDelegate.persistentContainer.viewContext
            if let entity = NSEntityDescription.entity(forEntityName: "Timers", in: context) {

                let newTimer = NSManagedObject(entity: entity, insertInto: context)
                newTimer.setValue(true, forKey: "active")

                let now = Date()
                newTimer.setValue(now, forKey: "appCloseTime")
                newTimer.setValue(self.time, forKey: "alreadyTimed")

                do {
                   try context.save()
                    print("object saved success")
                  } catch {
                   print("Failed saving")
                }
            }
        }
    }
}

编辑 - 这是在 xCode 11.3 和物理设备 iOS 13.2 上经过完整测试和工作的代码 - 您必须弄清楚如何根据您的按钮启动和停止计时器 - 但此示例只是在应用程序时启动计时器首次打开并且永远不会停止或重置它。

您可以通过创建一个新的单视图 xCode 项目并用上面的代码替换它为您创建的第一个视图控制器中的代码来重现这一点。然后创建一个标签以附加到 VC 上的插座timerLabel

• 还要确保在创建新项目时在项目中启用 CoreData * 然后在 xcdatamodel 文件中设置实体和属性：

希望对你有帮助