How to repeat every X seconds in Swift? - ios

Question

I am trying to build a simple single view app which runs an infinite slide show of a selection of images with a time delay between each image change.
The code I wrote for this is below. I tried to put this into viewDidLoad and viewDidAppear but the screen remained blank which I guess is because the function never finishes due to the infinite loop.
I learnt a bit of Python before iOS and with tkinter, your code would go into the mainloop. But I am not quite sure how to do the equivalent in Swift
Could someone please explain why I am having this problem and how to do this in Swift. Thanks.
var arrayimages: [UIImage] = [UIImage(named: "charizard")!,UIImage(named:"Flying_Iron_Man")!]
var x: Int = 0
var images: UIImage
let arraycount = arrayimages.count
repeat{
images = arrayimages[(x % arraycount)]
sleep(1)
slideshow.image = images
x++
} while true
NB: slideshow is an image view outlet.

Answer 1

You're looking for NSTimer
let timer = NSTimer.scheduledTimerWithTimeInterval(
1.0, target: self, selector: Selector("doYourTask"),
userInfo: nil, repeats: true)
The first argument is how frequently you want the timer to fire, the second is what object is going to have the selector that gets called, the third is the selector name, the fourth is any extra information you want to pass as a parameter on the timer object, and the fifth is whether this should repeat.
If you want to stop the code at any future point:
timer.invalidate()

Answer 2

Create a repeating NSTimer:
var timer = NSTimer.scheduledTimerWithTimeInterval(2.0,
target: self,
selector: "animateFunction:",
userInfo: nil,
repeats: true)
Then write a function animateFunction:
func animateFunction(timer: NSTimer)
{
//Display the next image in your array, or loop back to the beginning
}
Edit: Updated for modern Swift versions: (>= Swift 5)
This has changed a lot since I posted this answer. NSTimer is now called Timer in Swift, and the syntax of the scheduledTimer() method has changed. The method signature is now scheduledTimer(timeInterval:target:selector:userInfo:repeats:)
Also, the way you create a selector has changed
So the call would be
var timer = Timer.scheduledTimer(timeInterval: 2.0,
target: self,
selector: #selector(animateFunction(_:)),
userInfo: nil,
repeats: true)
And the animateFunction might look like this:
func animateFunction(timer: Timer)
{
//Display the next image in your array, or loop back to the beginning
}