Swift 3 Draggable UIButton - swift

Question

Apologies as I'm still learning the basics of Swift.
I'm trying to move a button when I drag it which sounds simple. I can't figure out how to pass along the sender information to the drag function so I can associate it with the button that is being dragged.
I create multiple one word buttons which are only text and attach a pan gesture recognizer to each of them:
let pan = UIPanGestureRecognizer(target: self, action: #selector(panButton(_:)))
let word = UIButton(type: .system)
word.addGestureRecognizer(pan)
I've created this function to trigger when the button is moved:
func panButton(sender: UIPanGestureRecognizer){
if sender.state == .began {
//wordButtonCenter = button.center // store old button center
} else if sender.state == .ended || sender.state == .failed || sender.state == .cancelled {
//button.center = wordButtonCenter // restore button center
} else {
let location = sender.location(in: view) // get pan location
//button.center = location // set button to where finger is
}
}
I'm getting the following error:
Use of unresolved identifier 'panButton'

Answer 1

First of all, your action needs to be a selector in Swift 3. So that would look something like this:
let pan = UIPanGestureRecognizer(target: self, action: #selector(panButton(_:))
Also, you can't pass the value of a button through a selector, so you would need to change your func to be:
func panButton(sender: UIPanGestureRecognizer){
...
}
If you're wondering how you are supposed to find the button if you can't pass it as a parameter, then you might consider using tags.

Answer 2

As #benjamin points out in Swift 3 you needs to be a selector. I've updated my code to the following in order to extract the button tag:
let panGesture = UIPanGestureRecognizer(target: self, action: #selector(self.panGestureHandler(panGesture:)))
panGesture.minimumNumberOfTouches = 1
let word = UIButton(type: .system)
With the following selector:
#objc func panGestureHandler(panGesture recognizer: UIPanGestureRecognizer) {
let buttonTag = (recognizer.view?.tag)!
if let button = view.viewWithTag(buttonTag) as? UIButton {
if recognizer.state == .began {
wordButtonCenter = button.center // store old button center
} else if recognizer.state == .ended || recognizer.state == .failed || recognizer.state == .cancelled {
button.center = wordButtonCenter // restore button center
} else {
let location = recognizer.location(in: view) // get pan location
button.center = location // set button to where finger is
}
}
}