NSTimer 倒计时产生两次 0

Question

我有一些代码可以获取今天和另一个时间字符串之间的时间差。

使用NSTimer.scheduledTimerWithTimeInterval每秒刷新显示。

除计时器达到 0 外，一切正常。0 显示两次。

示例：

3,2,1,0,0,-1,-2

下面是我在操场上完成的代码：

   //: Playground - Time Countdown
import UIKit
import XCPlayground
XCPSetExecutionShouldContinueIndefinitely()

class MyClass {

    var totalSecondsText = ""

    init(classSecondsText: String){
        totalSecondsText = classSecondsText
    }

    @objc func ontimer(timer:NSTimer!){

        let total = determineTimeDifference(totalSecondsText)

                let (hour,min,sec) = secondsConverter(total)

                if hour >= 1 {
                    if min >= 1 {
                        NSLog(String(hour)+"h "+String(min)+"m")
                    }else {
                        NSLog(String(hour)+"h")
                    }
                }else{
                    if min >= 1{
                        NSLog(String(min)+"m "+String(sec)+"s")
                    } else if min > -1 {
                        NSLog(String(sec)+"s")
                    } else if min <= -1 {
                        NSLog(String(min)+"m")
                    }
                }
    }

    func determineTimeDifference(timeInputed: String) -> Int {

         let dateFormat = NSDateFormatter()
         dateFormat.dateFormat = "yyyy-MM-dd'T'HH:mm:ssZ"
         let finalDate = dateFormat.dateFromString(raceTime)
         let differenceTimeInSeconds =  (finalDate?.timeIntervalSinceNow)!

    return differenceInSeconds

   }

    func secondsConverter (seconds : Int) -> (Int  , Int, Int){
        return (seconds / 3600, (seconds % 3600) / 60, (seconds % 3600) % 60)
    }

}

// Add +1 minute on time to test.
var dateString = "2016-08-31T6:49:00Z"

NSTimer.scheduledTimerWithTimeInterval(1, target: MyClass(classSecondsText: dateString), selector: #selector(MyClass.ontimer(_:)), userInfo: nil, repeats: true)

知道哪里出了问题吗？

更新：

正如所承诺的，这是针对此问题的错误修复：

    func determineTimeDifference(timeInputed: String) -> Int {

             let dateFormat = NSDateFormatter()
             dateFormat.dateFormat = "yyyy-MM-dd'T'HH:mm:ssZ"
             let finalDate = dateFormat.dateFromString(raceTime)?.timeIntervalSince1970
             let dateNow = NSDate().timeIntervalSince1970
             let differenceTimeInSeconds = Int(finalDate) -  Int(dateNow)

     return differenceInSeconds
}

Answer 1

您的代码提供得很好，并且条件设置正确。看起来 Data.components 没有正确处理计数差异。这可能是由秒分量的舍入引起的。

如果在时刻之前计数，当当前时间和最终时间相等时，（达到0,0），结果带有-1的错误.

当我用额外的打印更新您的代码时，显示如下：

CURRENT date: 2016-08-31 13:10:57 +0000 - FINAL date: 2016-08-31 13:11:00 +0000
-->> diff by DateComponents: 2s (BAD)
CURRENT unix: 1472649057.28685 - FINAL unix: 1472649060.0
--->>> Diff in UNIX:  -3.0s (counted as Rounded CURRENT UNIX - FINAL UNIX)
2s 

CURRENT date: 2016-08-31 13:10:58 +0000 - FINAL date: 2016-08-31 13:11:00 +0000
-->> diff by DateComponents: 1s (BAD)
CURRENT unix: 1472649058.28734 - FINAL unix: 1472649060.0
--->>> Diff in UNIX:  -2.0s (counted as Rounded CURRENT UNIX - FINAL UNIX)
1s 

CURRENT date: 2016-08-31 13:10:59 +0000 - FINAL date: 2016-08-31 13:11:00 +0000
-->> diff by DateComponents: 0s (BAD)
CURRENT unix: 1472649059.28731 - FINAL unix: 1472649060.0
--->>> Diff in UNIX:  -1.0s (counted as Rounded CURRENT UNIX - FINAL UNIX)
0s 

CURRENT date: 2016-08-31 13:11:00 +0000 - FINAL date: 2016-08-31 13:11:00 +0000
-->> diff by DateComponents: 0s (OK)
CURRENT unix: 1472649060.28731 - FINAL unix: 1472649060.0
--->>> Diff in UNIX:  0.0s (counted as Rounded CURRENT UNIX - FINAL UNIX)
0s 

CURRENT date: 2016-08-31 13:11:01 +0000 - FINAL date: 2016-08-31 13:11:00 +0000
-->> diff by DateComponents: -1s (OK)
CURRENT unix: 1472649061.28731 - FINAL unix: 1472649060.0
--->>> Diff in UNIX:  1.0s (counted as Rounded CURRENT UNIX - FINAL UNIX)
-1s 

CURRENT date: 2016-08-31 13:11:02 +0000 - FINAL date: 2016-08-31 13:11:00 +0000
-->> diff by DateComponents: -2s (OK)
CURRENT unix: 1472649062.28729 - FINAL unix: 1472649060.0
--->>> Diff in UNIX:  2.0s (counted as Rounded CURRENT UNIX - FINAL UNIX)
-2s

因此，如果使用四舍五入的 unix 时间之间的差异进行计数，结果是正确的。

结论：错误有时出现在方程之前，有时出现在方程之后。这取决于该脚本启动的时间。如果按数据组件计数以错误开始，则在 0、0 之后进行清理。如果以正确结果开始计数，则结果开始带来错误结果。这就是零出现两次的原因 - 在结果改变其精确状态的那一刻。

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