IOS: Updating Labels in a UITableViewCell using an NSTimer

Question

I'm trying to create a countdown app that will show the number of Years....Seconds until an upcoming date. I want to be able to view several countdowns in a table view. I have some basic logic that works idependently of a tableview cell to create the countdown:

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var timer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: "countdown", userInfo: nil, repeats: true)

func  countdown() {
    let hourMinuteComponents: NSCalendarUnit =
        NSCalendarUnit.CalendarUnitYear |
        NSCalendarUnit.CalendarUnitMonth |
        NSCalendarUnit.CalendarUnitDay |
        NSCalendarUnit.CalendarUnitHour |
        NSCalendarUnit.CalendarUnitMinute |
        NSCalendarUnit.CalendarUnitSecond
    let timeDifference = userCalendar.components(
        hourMinuteComponents,
        fromDate: NSDate(),
        toDate: date1.enteredDate as NSDate,
        options: nil)
// Sample Output
    println("Year: \(timeDifference.year)")
    println("Month: \(timeDifference.month)")
    println("Day: \(timeDifference.day)")
    println("Hour: \(timeDifference.hour)")
    println("Minute: \(timeDifference.minute)")
    println("Second: \(timeDifference.second)")
}

This works well and the console shows the countdown. However, I can't get past an error when I try to call it from a cell.

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFTimer row]: unrecognized selector sent to instance

Here's the code that isn't working.

override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
    println("Index Path: \(indexPath)")
    let cell = tableView.dequeueReusableCellWithIdentifier("countDownCell") as! UITableViewCell
    let cellIndex = indexPath
    var timer = NSTimer.scheduledTimerWithTimeInterval(1, target: self, selector: "update:", userInfo: cellIndex, repeats: true)
    //let secondlabel = cell.viewWithTag(1005) as! UILabel
    //secondlabel.text = "Test"


    return cell

}


func  update(cellIndex: NSIndexPath) {
    let hourMinuteComponents: NSCalendarUnit =
    NSCalendarUnit.CalendarUnitYear |
    NSCalendarUnit.CalendarUnitMonth |
    NSCalendarUnit.CalendarUnitDay |
        NSCalendarUnit.CalendarUnitHour |
        NSCalendarUnit.CalendarUnitMinute |
        NSCalendarUnit.CalendarUnitSecond
    let timeDifference = userCalendar.components(
        hourMinuteComponents,
        fromDate: NSDate(),
        toDate: date1.enteredDate as NSDate,
        options: nil)
    println("Year: \(timeDifference.year)")
    println("Month: \(timeDifference.month)")
    println("Day: \(timeDifference.day)")
    println("Hour: \(timeDifference.hour)")
    println("Minute: \(timeDifference.minute)")
    println("Second: \(timeDifference.second)")


    if let cell = tableView.cellForRowAtIndexPath(cellIndex) {
        let yearlabel = cell.viewWithTag(1000) as! UILabel
        let secondlabel = cell.viewWithTag(1005) as! UILabel!
    }

    secondlabel.text = "\(timeDifference.second)"


}

I appreciate any help you can provide. I initially focused my fixing attempts on changing how I'm calling update() from the timer. I tried passing the cell explicitly and then thought it better to try calling the indexPath of the cell. I also checked my syntax as was suggested in a number of NSTimer posts. I think I have it right (and believe I've tried pretty much all other options).

The code breaks at this line:

if let cell = tableView.cellForRowAtIndexPath(cellIndex) { ...

Answer 1

The selector passed to NSTimer's scheduledTimerWithTimeInterval(_:target:selector:userInfo:repeats:) receives a NSTimer object, not a NSIndexPath.

That is, your update(_:) method should be defined as

func update(timer: NSTimer) {
    cellIndex = timer.userInfo as! NSIndexPath
    ...
}

See the method's documentation for more information