如何在 Swift 中为两个日期减法运行计时器

Question

*我有两个约会。 那些，我必须在UTC中做日期格式，然后必须做两个日期的减法。 我必须为剩余时间运行计时器。 一旦达到 0 秒，我就必须停止计时器，并且必须调用一些 api。

从日期：2021-07-21T09:04:38.306Z，到日期：2021-07-21T09:06:08.000Z

    override func viewDidLoad() {
        super.viewDidLoad()

let when = DispatchTime.now() + 0.1 // change 2 to desired number of seconds
                    DispatchQueue.main.asyncAfter(deadline: when) {
                        self.countDownTimer = Timer.scheduledTimer(timeInterval: 1.0, target: self, selector: #selector(MyViewController.countDownTime), userInfo: nil, repeats: true)
                    }

}

  @objc func countDownTime() {
        
        let unlockDuration = self.getCountDownTime(currentTime: "2021-07-21T09:04:38.306Z" , unlockTime: "2021-07-21T09:06:08.000Z")
        if unlockDuration == "0d :0h : 0: 0" {
            self.stopTimer()
        }
    }
    
    func stopTimer(){
            guard self.countDownTimer != nil else {
                fatalError("No timer active, start the timer before you stop it.")
            }
            self.countDownTimer?.invalidate()
            self.callAPI()
        }

  func getCountDownTime(currentTime: String, unLockTime: String) -> String {
        
        let dateFormatter = DateFormatter()
        dateFormatter.dateFormat = "yyyy-MM-dd HH:mm:ssZ"
        dateFormatter.timeZone = TimeZone(abbreviation: "UTC")
        let unlockDate = dateFormatter.date(from: "\(unlockTime)") ?? Date()
        let currentDate = dateFormatter.date(from: "\(currentTime)") ??  Date()
        print(currentDate)
        print(unlockDate)
        let calendar = Calendar.current
        let diffDateComponents = calendar.dateComponents([.day, .hour, .minute, .second], from: unlockDate, to: currentDate)
        let countdown = "\(String(describing:diffDateComponents.day!))d :\(String(describing: diffDateComponents.hour!))h : \(String(describing: diffDateComponents.minute!)): \(String(describing: diffDateComponents.second!))"

        print(countdown)
        return countdown
        
    }

func callAPI() {
//Calling api here
}

但是，始终将其打印为 0d :0h : 0: 0 并且不显示秒，分钟它的打印始终如下所示

2021-07-21 11:14:23 +0000
2021-07-21 11:14:23 +0000
0d :0h : 0: 0

有什么建议么？*

Answer 1

要使用此格式解析日期：

2021-07-21T09:04:38.306Z

采用

dateFormatter.dateFormat = "yyyy-MM-dd'T'HH:mm:ss.SSSZ"

因为dateFormatter.date(from: "\\(unlockTime)")返回 nil，所以你得到 0 的差异，所以你从Date()减去Date()并得到 0 差异。