Breathing animation in Xcode-Swift while app being responsive

Question

I am trying to have a image of a star "breathe" in a loop. Getting bigger and then smaller and then repeating itself. I want this to continue while my app is still running and being responsive. And when I go to another view in my app , then I want the animation to stop.

Here is what I got

    override func viewDidLoad() {
    super.viewDidLoad()

    DispatchQueue.main.async {
            self.animateStars()
    }
}

func animateStars() {
  UIView.animate(withDuration: 4, animations : {
        self.star.transform = CGAffineTransform(scaleX: 2.5, y: 2.5)

    }) { finished in
        NSLog("Star is big. Finished = \(finished)")
    }

    UIView.animate(withDuration: 4, animations : {
        self.star.transform = CGAffineTransform(scaleX: 0.5, y: 0.5)

    }) { finished in
        NSLog("Star is small. Finished = \(finished)")
    }
}

This does not loop tough. And I dont know how to make it loop without it running like mad in the background, when the user click on a button with segue, to go to another view.

I have found one solution in Objective C, but I cant seem to understand how I should translate it to Swift 3.0. Example here: https://stackoverflow.com/a/31978173/5385322

 [UIView animateWithDuration:1
                  delay:0
                options:UIViewKeyframeAnimationOptionAutoreverse | UIViewKeyframeAnimationOptionRepeat
             animations:^{
                 yourView.transform = CGAffineTransformMakeScale(1.5, 1.5);
             }
             completion:nil];

Thank you for your time and suggestions! //Simon

Answer 1

The Swift version of the Objective-C repeating animation code you posted would be:

UIView.animate(withDuration: 1.0,
               delay: 0,
               options: [.autoreverse, .repeat, .allowUserInteraction],
               animations: {
                self.star.transform = CGAffineTransform(scaleX: 1.5, y: 1.5)
},
               completion: nil

)

(In Swift, most option flag parameters like the options parameter in that animation code are of type OptionSet, which is bit flags that supports Swift Set syntax, so you list the options you want in square brackets, separated by commas.

Note that @TungFam's solution would not work as written, but you COULD use that approach if you used a completion block that checked an animate boolean and re-invoked the animation method if it was true.

EDIT:

If you want to stop the animation, use

self.star.layer.removeAllAnimations()
self.star.layer.transform = CGAffineTransform.identity

EDIT #2:

If you want to be able to start and stop an animation at will, you can use code like this:

func animateView(_ view: UIView, animate: Bool) {
  if animate {
    UIView.animate(withDuration: 1.0,
                   delay: 0,
                   options: [.autoreverse, .repeat, .allowUserInteraction],
                   animations: {
                    view.transform = CGAffineTransform(scaleX: 1.5, y: 1.5)
    },
                   completion: nil

    )
  } else {
    self.button.layer.removeAllAnimations()
    UIView.animate(withDuration: 1.0,
                   delay: 0,
                   options: [.curveEaseOut, .beginFromCurrentState, .allowUserInteraction],
                   animations: {
                    view.transform = CGAffineTransform.identity
    },
                   completion: nil

    )
  }
}

That code will cause the view to smoothly animated back to normal size when the animation is stopped. It also adds the .allowUserInteraction flag to the animation, in case the view you're animating is a button that you want to be able to tap on while it's size is changing.

Answer 2

Try to add the variable that holds the bool value that says either it needs to animate or not. and change it when user taps the button to go to next screen.

Something like this:

var animate = true

override func viewDidLoad() {
   super.viewDidLoad()

   self.animateStars()
}

func animateStars() {
  while animate == true   {
    // breathing animation
  }
}

@IBAction func buttonPressed(_ sender: UIButton) {
   animate = false

   // perform your segue
}

if you want to animate it back again when the user comes back to this screen then place self.animateStars() to the viewWillAppear method.

Answer 3

With some insights from @DuncanC I was able to get this to work quite well. The animation now stops when I go to another view and continues when I get back to the original view.

The code looks like this:

class MainViewController: UIViewController {

@IBOutlet weak var star: UIImageView!

var queue = DispatchQueue.main

  override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    self.star.layer.removeAllAnimations()
    self.star.transform = CGAffineTransform.identity

    queue.async {
        self.animateStars()
    }
}
    @IBAction func someAction(_ sender: Any) {
    performSegue(withIdentifier: "someSegue", sender: self)
    }

    func animateStars() {
    UIView.animate(withDuration: 1,
                   delay: 0,
                   options:[.autoreverse, .repeat],
                   animations : {
                    self.star.transform = CGAffineTransform(scaleX: 2.5, y: 2.5)})
    { finished in
        UIView.animate(withDuration: 1.0,
                       delay: 0,
                       options: [.curveEaseOut, .beginFromCurrentState],
                       animations: {
                        self.star.transform = CGAffineTransform.identity
        },
                       completion: nil
        )
    }
    UIView.animate(withDuration: 1, 
                   delay: 0, 
                   options: [.autoreverse, .repeat], 
                   animations: { self.star.transform = CGAffineTransform(scaleX: 2.5, y: 2.5) })
}
}

I'm very new to programming still, going to school for it, and so far I havent learned about testing that much. Because of that, I havent tested this for memoryleaks and whatnots. But the code works and that means I'm happy for the time being.

Thank you all for your help! And do come with suggestions if your think you can improve on the code. :)

//Simon