Custom Function's CompletionHandler for Dummies - ios

Question

I searched everywhere on the internet but couldn't really deal with the answers I found. So if someone could help me here, that'd be appreciated.
I wrote a function that looks like this:
func setImage(imageName: String, completion: ((String) -> Void)?) {
UIView.transitionWithView(self.myImageView, duration: 0.3, options: .CurveEaseOut, animations: {
self.lockImageView.image = UIImage(named: "\(imageName).png")
}, completion: { finished in
//execute the completionBlock that was passed
})
}
I call it like this:
setImage("lockCheck", completion: { finished in
print("done")
})
Now, how do I execute whatever was passed as completion?
In the function, in the transition's completion block, I tried something like
for x in completion {self.x}
but that didn't work.
Thanks in advance :)

Answer 1

You could for example execute the completion handler right away in the completionHandler of the animation block like so:
func setImage(imageName: String, completion: ((Bool) -> Void)?) {
UIView.transitionWithView(self.myImageView, duration: 0.3, options: .CurveEaseOut, animations: { () -> Void in
self.lockImageView.image = UIImage(named: "\(imageName).png")
}, completion: completion)
}
You can also run an completion handler with extra parameters like the following (I hope it is clear like this):
func setImage(imageName: String, completion: ((Bool, String) -> Void)?) {
UIView.transitionWithView(self.lockImageView, duration: 0.3, options: .CurveEaseOut, animations: { () -> Void in
self.lockImageView.image = UIImage(named: "\(imageName).png")
}) { (finished) -> Void in
// Do some things for example print
print("Hi, this is the animation completion handler")
// Notice the ? because the completion handler is an optional
completion?(finished, "some string")
}
}