从创建对象开始设置计时器倒计时

Question

我正在 Parse 中的多个对象中查询 createdAt 日期。我想创建一个 24 小时（或 48/72 等）倒计时计时器，该计时器从创建对象到 24 小时后倒计时。 （我也在格式化它，并在单元格 UILabel 上显示它。）

示例：如果一个对象是在 19:34:33 创建的，我希望它在 24 小时后过期（或者我在创建后指定多少小时）。最终在 UILabel 上显示距离对象过期的时间。

目前，我正在检索它的创建时间，使其从创建时间开始重复倒计时。

但是，我想制定逻辑，以便在创建对象时需要它，然后显示在 24 小时或 48 小时、72 小时等结束之前还剩多少小时。

编辑

感谢@pulsar，我在下面的描述中添加了几行代码。现在的问题是我只能检索并正确倒计时 1 个对象的 createdAt 日期和时间，因为 仅 查询第一个对象，使所有其他对象都具有在它们各自的 indexPath.row 中与 Parse 中的第一个对象相同的过期 countDown 计时器。

我不知道如何添加所有对象，以便它们都有自己的由 expiresAt 函数触发的 countDown 过期时间。

以下是我查询和格式化它的方式（在 viewDidLoad 中）： 这是我问的帮助我格式化日期的问题：Swift countDown timer Logic

请看代码中的 cmets！

            var createdAt = object.createdAt
            if createdAt != nil {


                 //assuming this is where i have to set expiration logic?

                let calendar = NSCalendar.currentCalendar()
                let comps = calendar.components([.Hour, .Minute, .Second], fromDate: createdAt as NSDate!)
                let hours = comps.hour  * 3600
                let minutes = comps.minute * 60
                let seconds = comps.second

                 //I'm adding these two lines below but not sure what to do with them considering I need to add all the objects to an array that will then display it on indexPath.row(s)

                   let twentyFourHours = NSTimeInterval(60 * 60 * 24)
                    self.expiresAt = NSDate(timeInterval: twentyFourHours, sinceDate: object.createdAt!!)


                self.timerInt.append(hours + minutes + seconds)
                //What do i append to the timerInt array? How can i append the objects while triggering the the expiresAt function? 

           } 

这是我的倒计时功能：

               func countDown() {

        //timerInt is an array where I'm storing the Int values.
        for i in 0 ..< timerInt.count {

            let hours = timerInt[i] / 3600 
          //have to somehow add the expiresAt method while looping through each value [i]...?
            let minsec = timerInt[i] % 3600
            let minutes = minsec / 60
            let seconds = minsec % 60
       print(String(format: "%02d:%02d:%02d", hours, minutes, seconds))
          timerInt[i]--

           //Im assuming best practice would be to loop through the values in order to change the values/set the expiration time to each object (the expiresAt method). Any ideas of how and where I can add this in this loop so that it reflects the countDown I want to set?

        }

        self.tableView.reloadData()

}

最后，对于我的 indexPath.row，我将其格式化并显示如下：

          override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
         let myCell = tableView.dequeueReusableCellWithIdentifier("cell", forIndexPath: indexPath) as! cell

  //I'm formatting the hours, minutes, seconds. However I'm missing the expiresAt function and I have no clue as to where and how to include it... Should it be here or in the countDown() loop?  

     let hours = timerInt[indexPath.row] / 3600
     let minsec = timerInt[indexPath.row] % 3600
     let minutes = minsec / 60
     let seconds = minsec % 60


      myCell.secondLabel.text = String(format: "%02d:%02d:%02d", hours, minutes, seconds)


        return myCell
}

关于如何将其设置为从创建之日起 24/48/72 小时后倒计时的想法？

非常感谢任何和所有帮助！

Answer 1

听起来您需要设置到期日期，然后获取当前日期和到期日期之间的日期组件。然后您可以使用NSTimer 来刷新显示。 （完成后别忘了致电NSTimer.invalidate()）。

一个例子：

class YourViewController: UIViewController {

    var expiresAt: NSDate?

    func viewDidLoad() {
        // your parse logic here
        let twentyFourHours = NSTimeInterval(60 * 60 * 24)
        expiresAt = NSDate(timeInterval: twentyFourHours, sinceDate: createdAt)
        scheduleTimer()
    }

    func scheduleTimer() {
        NSTimer.scheduledTimerWithTimeInterval(1.0 / 30.0, target: self, selector: "tick:", userInfo: nil, repeats: true)
    }

    @objc
    func tick(timer: NSTimer) {
        guard let expiresAt = expiresAt else {
            return
        }
        let calendar = NSCalendar(calendarIdentifier: NSCalendarIdentifierGregorian)
        if let components = calendar?.components([.Hour, .Minute, .Second], fromDate: NSDate(), toDate: expiresAt, options: []) {
            print(formatDateComponents(components))
        }
    }

    func formatDateComponents(components: NSDateComponents) -> String {
        let hours = components.hour
        let minutes = components.minute 
        let seconds = components.second
        return "\(hours):\(minutes):\(seconds)"
    }

}

您还可以通过使用结构来存储日期组件而不是对 timerInt 字符串进行复杂的解析，从而使您的生活更轻松。

struct Time {
    let hours: String
    let minutes: String
    let seconds: String
}

Answer 2

//: Playground - noun: a place where people can play

import XCPlayground
XCPlaygroundPage.currentPage.needsIndefiniteExecution = true
import UIKit

class MyView: UIView {
    weak var l1: UILabel?
    weak var l2: UILabel?
    weak var l3: UILabel?

    let validFor: NSTimeInterval
    var validTo: NSDate = NSDate()

    lazy var timer: NSTimer = NSTimer(timeInterval: self.validFor, target: self, selector: "done", userInfo: nil, repeats: false)

    init(validFor: NSTimeInterval) {
        self.validFor = validFor
        super.init(frame: CGRect(x: 0, y: 0, width: 500, height: 100))
        validTo = timer.fireDate

        let ll1 = UILabel(frame: CGRect(x: 1, y: 1, width: 498, height: 30))
        ll1.text = "created at: \(NSDate())"
        self.addSubview(ll1)
        l1 = ll1

        let ll2 = UILabel(frame: CGRect(x: 1, y: 33, width: 498, height: 30))
        ll2.text = "valid to: \(validTo)"
        self.addSubview(ll2)
        l2 = ll2

        let ll3 = UILabel(frame: CGRect(x: 1, y: 66, width: 498, height: 30))
        ll3.text = "valid for next: \(validTo.timeIntervalSinceNow) second"
        self.addSubview(ll3)
        l3 = ll3

        NSRunLoop.currentRunLoop().addTimer(timer, forMode: NSRunLoopCommonModes)
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    // when MyView expires it trigers this function
    // and give me a chance to update UI
    func done() {
        // update UI
        dispatch_async(dispatch_get_main_queue(), { [unowned self] () -> Void in
            self.l2?.text = "     EXPIRED"
            self.l3?.text = ""
            if let text1 = self.l1?.text,
                let text2 = self.l2?.text,
                let text3 = self.l3?.text
            {
                print("")
                print(text1, text2, text3)

            }
        })
    }
    func updateState() {
        // periodically updating UI on request
        if timer.valid {
            let v = validTo.timeIntervalSinceNow

            // update UI
            dispatch_async(dispatch_get_main_queue(), { [unowned self] () -> Void in
                self.l3?.text = "valid for next: \(v) second"
                if let text1 = self.l1?.text,
                    let text2 = self.l2?.text,
                    let text3 = self.l3?.text
                {

                    print(text1, text2, text3)


                }
            })
        }
    }
}


let c = MyView(validFor: 10.0) // in seconds

let queue = dispatch_queue_create("update", DISPATCH_QUEUE_SERIAL)

// periodic action tu update UI
// in regular intervals
// this is just for demonstration, avoid using use sleep
// in real application
dispatch_async(queue) { () -> Void in
    repeat {
        c.updateState()
        sleep(3)
    } while true
}

dispatch_async(dispatch_get_main_queue(), { () -> Void in
    print("the app is running and responding on user actions")
    print("MyView labels are updating 'automatically'\n")
})

print("playground continue ....\n")