Days countdown iOS swift

Question

My app requires that I start countdown of days from first launch. If someone launch my app for the first time I want to count day 1 after 12 midnight (using the device clock of course) and then day2 ... and perform an action after the 21st day. It shouldn't matter if the person close the app or switch off phone. When the app come back up, it should automatically detect how many days have passed.

Does anyone have an idea how to realise that ? . I am thinking of NStimer but kind of confuse.

Answer 1

I think you want to use UILocalNotification. That would allow you to alert the user regardless if your app is active or not.

Please consult the documentation here, do a trial implementation and ask a new stack overflow question if you get stuck and cannot find an answer.

Answer 2

Ok, After fiddling around for some time and tried several stuffs in playground, I came up with a solution that work just perfect. So in case someone is trying to work out something similar, here is my solution.

    func checkElapsedDay (){

    //make sure the date register only run 1 time.
    if NSUserDefaults.standardUserDefaults().boolForKey("firstLaunch"){

        lauchDate =  NSUserDefaults.standardUserDefaults().objectForKey("start")! as! NSDate
        endDate = NSUserDefaults.standardUserDefaults().objectForKey("end")! as! NSDate
    }
    else{

        NSUserDefaults.standardUserDefaults().setBool(true, forKey: "firstLaunch")
        NSUserDefaults.standardUserDefaults().synchronize()

        endDate = lauchDate.dateByAddingTimeInterval(1814400) // 1814400 = 21 days
        NSUserDefaults.standardUserDefaults().setObject(lauchDate, forKey: "start")
        NSUserDefaults.standardUserDefaults().setObject(endDate, forKey: "end")
    }

    var today = NSDate()
    let compareResult = today.compare(endDate)
    let cal = NSCalendar.currentCalendar()
    let unit:NSCalendarUnit = .CalendarUnitDay
    let components = cal.components(unit, fromDate: today, toDate: endDate, options: nil)
    let biss = cal.compareDate(today, toDate: endDate, toUnitGranularity: nil)
    var bbb = components.day
    daysleft.image = UIImage(named: "\(bbb).png") //change the remaining day stamp

}