How to stop a Function from Running in Swift 3.0

Question

I have a function that starts playing an animation that is running asynchronously (in the background). This animation is called indefinitely using a completion handler (see below). Is there a way to close this function upon pressing another button?

Here is my code:

func showAnimation() {
    UIView.animate(withDuration: 1, animations: {
        animate1(imageView: self.Anime, images: self.animation1)
    }, completion: { (true) in
        DispatchQueue.main.asyncAfter(deadline: .now() + 2.0) {
            self.showAnimation() // replay first showAnimation
        }
    }) 
 }

Then upon pressing another button we closeout the above function

showAnimation().stop();

Thanks

Answer 1

You can add a property to the class to act as a flag indicating whether the animation should be run or not.

var runAnimation = true

func showAnimation() {
    if !runAnimation { return }

    UIView.animate(withDuration: 1, animations: {
        animate1(imageView: self.Anime, images: self.animation1)
    }, completion: { (true) in
        DispatchQueue.main.asyncAfter(deadline: .now() + 2.0) {
            if runAnimation {
                self.showAnimation() // replay first showAnimation
            }
        }
    }) 
}

Then in the button handler to stop the animation you simply do:

runAnimation = false

Note that this does not stop the currently running 1 second animation. This just prevent any more animations.

Answer 2

There are a lot of ways to do this. The simplest is to have a Boolean property (which you should make properly atomic) that you check in your asyncAfter block, and don't just don't call showAnimation() again if it's true.

Another thing you can do, and what I like to do for more complex tasks, is to use OperationQueue instead of DispatchQueue. This allows you to cancel operations, either individually or all at once, or even suspend the whole queue (obviously don't suspend the main queue or call removeAllOperations() on it, though, since there may be other operations in there unrelated to your code).