当应用程序在后台/暂停运行时继续倒数计时器 [英] Continue countdown timer when app is running in background/suspended

问题描述

我有一个功能性的倒数计时器.

I have a functional countdown timer.

问题是，当用户将应用置于后台时，我需要继续倒数计时.或暂停应用程序?我不确定描述此操作的正确术语是什么.

The problem is that I need to continue the countdown when the user puts the app in the background. Or suspends the app? I am not sure what the correct terminology is to describe this action.

换句话说，用户打开应用程序并开始倒计时.用户应该可以使用其他应用，但倒数计时仍然有效.另外，倒计时应该可以永久运行，直到完成或用户终止运行应用程序为止.

In other words, the user opens the app and starts the countdown. The user should be able to use other apps but the countdown still operate. Also, the countdown should be able to run forever until it finishes or when the user terminates running the app.

这是我的计时器的代码:

Here is the code for my timer:

    class Timer{
var timer = NSTimer();
// the callback to be invoked everytime the timer 'ticks'
var handler: (Int) -> ();
//the total duration in seconds for which the timer should run to be set by the caller
let duration: Int;
//the amount of time in seconds elapsed so far
var elapsedTime: Int = 0;
var targetController = WaitingRoomController.self

var completionCallback: (() -> Void)!



/**
:param: an integer duration specifying the total time in seconds for which the timer should run repeatedly
:param: handler is reference to a function that takes an Integer argument representing the elapsed time allowing the implementor to process elapsed time and returns void
*/
init(duration: Int , handler : (Int) -> ()){
    self.duration = duration;
    self.handler = handler;
}

/**
Schedule the Timer to run every 1 second and invoke a callback method specified by 'selector' in repeating mode
*/
func start(){
    self.timer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: "onTick", userInfo: nil, repeats: true);
}

/**
invalidate the timer
*/
func stop(){
    println("timer was invaidated from stop()")
    timer.invalidate();
}


/**
Called everytime the timer 'ticks'. Keep track of the total time elapsed and trigger the handler to notify the implementors of the current 'tick'. If the amount of time elapsed is the same as the total duration for the timer was intended to run, stop the timer.
*/


@objc func onTick() {
    //println("onTick")
    //increment the elapsed time by 1 second
    self.elapsedTime++;
    //Notify the implementors of the updated value of elapsed time
    self.handler(elapsedTime);
    //If the amount of elapsed time in seconds is same as the total time in seconds for which this timer was intended to run, stop the timer
    if self.elapsedTime == self.duration {
        self.stop();

    }
}
deinit{
    println("timer was invalidated from deinit()")
    self.timer.invalidate();
}

}

推荐答案

我建议取消计时器，并在应用程序进入后台时存储NSDate. 您可以使用此通知来检测应用程序进入后台:

What I suggest is cancel the timer and store a NSDate when the app goes to the background. You can use this notification to detect the app going to the background:

NSNotificationCenter.defaultCenter().addObserver(self, selector: "pauseApp", name: UIApplicationDidEnterBackgroundNotification, object: nil)

然后取消计时器并存储日期:

Then cancel the timer and store the date:

func pauseApp(){
    self.stop() //invalidate timer
    self.currentBackgroundDate = NSDate()
}

使用此通知来检测用户回来:

Use this notification to detect the user coming back:

NSNotificationCenter.defaultCenter().addObserver(self, selector: "startApp", name: UIApplicationDidBecomeActiveNotification, object: nil)

然后计算从存储日期到当前日期的差额，更新您的计数器并再次启动计时器:

Then calculate the difference from the stored date to the current date, update your counter and start the timer again:

func startApp(){
    let difference = self.currentBackgroundDate.timeIntervalSinceDate(NSDate())
    self.handler(difference) //update difference
    self.start() //start timer
}

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