How do I make a label keep switching between two colors in Swift? - swift

Question

I am trying to make my label flash two colors on repeat. I want it to continuously repeat the text color Blue and Black. Is this possible? And can someone help me do this?

Answer 1

You can do it by using NSTimer and below is complete code for that:
import UIKit
class ViewController: UIViewController {
#IBOutlet weak var lbl: UILabel!
var timer : NSTimer?
override func viewDidLoad() {
super.viewDidLoad()
timer = NSTimer.scheduledTimerWithTimeInterval(0.4, target: self, selector: "update", userInfo: nil, repeats: true)
}
var textColorIsBlue = false
func update() {
if !textColorIsBlue {
lbl.textColor = UIColor.blueColor()
} else {
lbl.textColor = UIColor.blackColor()
}
textColorIsBlue = !textColorIsBlue
}
}
And your result will be:
And you can modify timer as per your need.
And whenever you don't need time you can stop it by using timer?.invalidate().

Answer 2

I couldn't help but create an alternative example
class ViewController: UIViewController {
#IBOutlet private var label: UILabel! {
didSet {
label.text = "This is just some sample text"
}
}
private var timer: dispatch_source_t?
private var generator: AlternatingColorGenerator?
deinit {
guard let timer = timer else { return }
dispatch_source_cancel(timer)
}
override func viewDidLoad() {
super.viewDidLoad()
generator = AlternatingColorGenerator(colors: [.redColor(), .blueColor(), .greenColor()])
let t = repeatingTimer(1, queue: dispatch_get_main_queue()) { [weak self] () -> Void in
self?.label.textColor = self?.generator?.next()
}
dispatch_resume(t)
timer = t
label.textColor = generator?.next()
}
}
private class AlternatingColorGenerator: GeneratorType {
var currentIndex: Int = 0
let numberOfColors: Int
let colors: [UIColor]
init(colors: [UIColor]) {
self.colors = colors
numberOfColors = colors.count
}
func next() -> UIColor? {
let color = colors[currentIndex]
currentIndex = (currentIndex + 1) % numberOfColors
return color
}
}
private func repeatingTimer(interval: NSTimeInterval, queue: dispatch_queue_t, action: () -> Void) -> dispatch_source_t {
let timer = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue)
let timerInterval = UInt64(interval) * NSEC_PER_SEC
let timerLeeway = timerInterval / 10
dispatch_source_set_event_handler(timer, action)
dispatch_source_set_timer(timer, DISPATCH_TIME_NOW, timerInterval, timerLeeway)
return timer
}
This uses a GCD timer, rather than an NSTimer, and rather than toggle the colours with a method, I've created a generator.
This uses a different programming style: one where the generation of things (timers and colours to use) is separated from the place where they are consumed.