Jim Jim - 1 month ago 11
Swift Question

Argument of '#selector' does not 'refer' to an initializer or method

I have a method called

selectionDidFinish(controller:)
in a delegate to dismiss the viewController the delegate presented. The presented controller, which adopts my
Dismissable
protocol, has a
UIBarButtonItem
with an action attached to it that should call the
selectionDidFinish(controller:)
method but it's giving me the "Argument of '#selector' does not 'refer' to an initializer or method" error.

The error is in this presented
UIViewController
:

class FormulaInfoViewController: UIViewController, Dismissable {

weak var dismissalDelegate: DismissalDelegate?
override func viewDidLoad() {
super.viewDidLoad()

// Xcode doesn't like this selector
navigationItem.rightBarButtonItem = UIBarButtonItem(title: "Done", style: .Plain, target: self, action: #selector(dismissalDelegate?.selectionDidFinish(self)))
}

override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
}


I've confirmed that the
dismissalDelegate
is getting set properly to
FormulasTableViewController
so I can't understand why it can't see
dismissalDelegate?.selectionDidFinish(self))
.

The relevant code of my presenting
UIViewController
is:

class FormulasTableViewController: UITableViewController, DismissalDelegate {

let formulas: [CalculationFormula] = [
CalculationFormula.epley,
CalculationFormula.baechle,
CalculationFormula.brzychi,
CalculationFormula.lander,
CalculationFormula.lombardi,
CalculationFormula.mayhewEtAl,
CalculationFormula.oConnerEtAl]

override func viewDidLoad() {
super.viewDidLoad()

let liftInfoImage = UIImage(named: "info_icon")
let liftInfoButton = UIBarButtonItem(image: liftInfoImage, style: .Plain, target: self, action: #selector(self.segueToFormulaInfo(_:)))
self.navigationItem.rightBarButtonItem = liftInfoButton
}

func selectionDidFinish(controller: UIViewController) {
self.dismissViewControllerAnimated(true, completion: nil)
}

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
let nav = segue.destinationViewController as! UINavigationController
let vc = nav.topViewController as! Dismissable
vc.dismissalDelegate = self
}

func segueToFormulaInfo(sender: UIButton) {
performSegueWithIdentifier("segueToFormulaInfo", sender: self)
}
}


I've done all kinds of research on how to use
#selector
and I thought this post had all the answers, but it doesn't.

I've tried this Dismissable protocol with and without exposing it to
@objc
:

@objc protocol Dismissable: class {
weak var dismissalDelegate: DismissalDelegate? {
get set }
}


And I've also tried it with my DismissalDelegate protocol:

@objc protocol DismissalDelegate : class {
func selectionDidFinish(controller: UIViewController)
}

extension DismissalDelegate where Self: UIViewController {
func selectionDidFinish(viewController: UIViewController) {
self.dismissViewControllerAnimated(true, completion: nil)
}
}


I can't expose my protocol extension to
@objc
- is that why this doesn't work? Is my
#selector
really the problem here? Does it have something to do with my protocols?

EDIT: Final fix

Based on the accepted answer, I added a function to do the dismissal:

func dismiss() {
dismissalDelegate?.selectionDidFinish(self)
}


and then called the selector like this:

navigationItem.rightBarButtonItem = UIBarButtonItem(title: "Done", style: .Plain, target: self, action: #selector(dismiss))

Answer

You can't have the action parameter specify an arbitrary expression. It needs to invoke a specific selector - a class and function in that class.

You will need to create a function in your class that invokes the delegate method:

class FormulaInfoViewController: UIViewController, Dismissable {

    weak var dismissalDelegate: DismissalDelegate?
    override func viewDidLoad() {
        super.viewDidLoad()

      navigationItem.rightBarButtonItem = UIBarButtonItem(title: "Done", style: .Plain, target: self, action: #selector(FormulaInfoViewController.selectionDidFinish)
    }  

    @objc func selectionDidFinish() {
        self.dismissalDelegate?.selectionDidFinish(self)
    }
}