NSTimeInterval as a countdown timer, applying it as a seperate reusable class - ios

Question

EDIT: I'm an idiot. I was trying to put the variable into NSTimer() and not NSTimeInterval for whatever silly reason. I guess my question is how can I wrap this all up in a separate class?
Ideally, I'd like all this wrapped up in a separate class (CountdownTimer), so I can create new instance of a timer but still retain all the functionality that NSTimer includes such as the ability to check timer.isValid. Psuedocode would look something like:
var timer = CountdownTimer(countDownFrom: 300)
timer.start()
timer.isValid()
My UIViewController class (not in viewDidLoad):
var totalCountDownTimeInterval = NSTimeInterval(480.0)
var startTime = NSDate()
var timer = NSTimer()
var isRunning = false
func updateTime() {
var elapsedTime : NSTimeInterval = NSDate().timeIntervalSinceDate(startTime)
var remainingTime : NSTimeInterval = totalCountDownTimeInterval - elapsedTime
if remainingTime <= 0.0 {
timer.invalidate()
}
let minutes = UInt8(remainingTime / 60.0)
remainingTime = remainingTime - (NSTimeInterval(minutes) * 60)
let seconds = UInt8(remainingTime)
println("The time is \(minutes) and \(seconds)")
}
#IBOutlet weak var TimerCount: UILabel!
#IBAction func StartButton(sender: AnyObject) {
if !timer.valid {
startTime = NSDate()
let aSelector : Selector = "updateTime"
timer = NSTimer.scheduledTimerWithTimeInterval(0.10, target: self, selector: aSelector, userInfo: nil, repeats: true)
}
}
#IBAction func StopButton(sender: AnyObject) {
timer.invalidate()
}
#IBAction func ResetButton(sender: AnyObject) {
timer.invalidate()
TimerCount.text = "00:00"
}

Answer 1

Make sure that you're actually passing in a double. I like to explicitly state the type of my variables when I declare them; it helps to avoid problems just like this.
You're most likely declaring doubleValue like this:
let doubleValue = 480
instead of like this:
let doubleValue = 480.0
or like this:
let doubleValue: Double = 480
If you've declared your variable correctly, this should work:
let timeInterval = NSTimeInterval(doubleValue)
If you are going to let the compiler infer the variable's type, just make sure that whatever's on the right side of your assignment operator evaluates to the type you're looking for. 480 evaluates to Int(480) while 480.0 evaluates to Double(480).
EDIT: Here's the answer to your second question: How can I wrap this [timer functionality] up in a separate class?
It's actually really simple. Assuming that all you want to do with the class is to be able to start it and check if it's still valid, here's how I would go about doing this:
class CountdownTimer
{
var time: NSTimeInterval
private var startTime: NSDate?
init(countDownFrom timeInSeconds: Int)
{
time = NSTimeInterval(timeInSeconds)
}
func start()
{
startTime = NSDate()
}
func isValid() -> Bool
{
if (startTime != nil)
{
let timePassed: NSTimeInterval = -(startTime!.timeIntervalSinceNow)
return timePassed < time
}
else
{
return false
}
}
}
Now, be warned, I barely tested this. Playground isn't complaining and from the looks of it, this should work. Now, just use the class like so:
var myCountdownTimer = CountdownTimer(countDownFrom: 300)
// and then whenever we want to start the countdown:
myCountdownTimer.start()
// and then whenever we want to check if the clock's still "ticking", so to speak:
myCountdownTimer.isValid()
// and if we want to restart the timer:
myCountdownTimer.time = NSTimeInterval(900) // we can change the time if we want
myCountdownTimer.start()
Essentially, all a CountdownTimer object does is save the exact time start() is called to a variable called startTime. Note that NSDate() by default is set to the time-and-date it's created. Then isValid() simply checks to see if the timePassed is less than whatever time the timer was set to count down from; if it is, then it returns true.

Answer 2

I tried this code on playground of Xcode 6.1, And It worked fine.
That's strange...
let someValue: Double = 60.0
var timeInterval = NSTimeInterval(someValue)
println(timeInterval)