Swift 3 Method from Class not working with #selector syntax - swift

Question

I feel as though I'm not understanding the Swift #selectors properly. I'm trying to connect a button to a method from another class.
I have a class to print the button when pushed:
class printThings {
#IBAction func printMe(_ sender: UIButton){
print("Button Pushed.")
}
}
And then the ViewController:
class ViewController : UIViewController {
override func ViewDidLoad(){
super.viewDidLoad()
//button setup here
let printMe = printThings()
button.addTarget(printMe, action: #selector(printMe.printMe(_:)), for: .touchUpInside)
//add button to subview
}
}
This never triggers the print statement in the class. I'm sure I'm missing something simple.
Thanks.

Answer 1

The problem is that printMe is a temporary, local variable:
let printMe = printThings() // local variable
button.addTarget(printMe, action: #selector(printMe.printMe(_:)), for: .touchUpInside)
// ... and then viewDidLoad ends, and `printMe` vanishes
So by the time you push the button, printMe has vanished; there is no one to send the button message to.
If you want this to work, you need to make printMe persist:
class ViewController : UIViewController {
let printMe = printThings() // now it's a _property_ and will persist
override func viewDidLoad(){
super.viewDidLoad()
//button setup here
button.addTarget(self.printMe, action: #selector(self.printMe.printMe(_:)), for: .touchUpInside)
//add button to subview
}
}