Create a blinking label

Question

Luise_2020 OP

Created Jan ’21

Replies 6

Boosts 0

Views 3.2k

Participants 3

I have a normal label and want that Label to blink three times, by changing the backgroundcolor from red to black an so on. I did some research and many people work with Timer or animations, but I cannot change this methods, like I need them. What can I do to make my Label blink?

Answered by OOPer in 656311022

I tired this in the viewDidLoad() function,

It would be better if you could show more context.

There's one very simple principle in iOS programming: NEVER call sleep.
(Never call blocking functions in the main thread.)

All the UI updates begins when the current task in the main thread is finished.
UI updates starts after viewDidLoad() is finished, meaning all the intermediate results are not shown and only the last result done in viewDidLoad() will be shown with very long delay.

As you wrote yourself, using Timer is one of the right ways:

Code Block         caption.backgroundColor = .black
        var backgroundColorIsRed = false
        var blinkCount = 0
        Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) {timer in
            backgroundColorIsRed.toggle()
            self.caption.backgroundColor = backgroundColorIsRed ? .systemRed : .black
            blinkCount += 1
            if blinkCount >= 4 {
                timer.invalidate()
            }
        }

Boost

Answer 1

OOPer OP

Jan ’21

What can I do to make my Label blink?

Please show what you have tried till now. Even if it may not work as you expect, that would be very useful to write an answer.

1

Answer 2

Luise_2020 OP

Jan ’21

I tired this in the viewDidLoad() function, but this does not show me the blinking, instead the View show up, when the for-loop has finished.

Code Block 	caption.backgroundColor = UIColor.black
        for _ in 0...2{
            var bool = false
                if bool{
                    caption.backgroundColor = UIColor.black
                    bool = false
                }
                else {
                    caption.backgroundColor = UIColor.systemRed
                    bool = true
            }
            sleep(1)
        }

0

Answer 3

OOPer OP

Jan ’21

Accepted Answer

I tired this in the viewDidLoad() function,

It would be better if you could show more context.

There's one very simple principle in iOS programming: NEVER call sleep.
(Never call blocking functions in the main thread.)

All the UI updates begins when the current task in the main thread is finished.
UI updates starts after viewDidLoad() is finished, meaning all the intermediate results are not shown and only the last result done in viewDidLoad() will be shown with very long delay.

As you wrote yourself, using Timer is one of the right ways:

Code Block         caption.backgroundColor = .black
        var backgroundColorIsRed = false
        var blinkCount = 0
        Timer.scheduledTimer(withTimeInterval: 1.0, repeats: true) {timer in
            backgroundColorIsRed.toggle()
            self.caption.backgroundColor = backgroundColorIsRed ? .systemRed : .black
            blinkCount += 1
            if blinkCount >= 4 {
                timer.invalidate()
            }
        }

1

Answer 4

Claude31 OP

Jan ’21

I did this with a UIView extension

Code Block extension UIView {  
    func flashIt(repeated: Int, cycleTime: Double, delayed: Double = 5.0) {
        if repeated < 0 { return }
        
        let initAlpha = self.alpha
        UIView.animate(withDuration: cycleTime,  //Time duration
            delay: delayed,
            options:[.allowUserInteraction, .curveEaseInOut, .autoreverse, .repeat],
            animations: {
                UIView.setAnimationRepeatCount(Float(repeated)) // repeat 3 times.
                self.alpha = 0.1    // Not 0.0, to allow user interaction
        },
            completion: { (done: Bool) in self.alpha = initAlpha } )
    }
}

In your case, instead of setting the alpha, just set the background color.
And restore it in completion.

1

Answer 5

Luise_2020 OP

Jan ’21

@OOPer thank you very much for you advice and the solution! It works like it should. Now I call a method in the viewDidLoad() called blinkred(), is that correct?

0

Answer 6

OOPer OP

Jan ’21

Now I call a method in the viewDidLoad() called blinkred(), is that correct?

It depends on how you implemented blinkred(), but I guess you have done it correctly if you can see the right result.

0