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

<p>The error is in this presented <code>UIViewController</code>:</p>

<pre><code>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.
    }
}
</code></pre>

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

<p>The relevant code of my presenting <code>UIViewController</code> is:</p>

<pre><code>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)
    }
}
</code></pre>

<p>I've done all kinds of research on how to use <code>#selector</code> and I thought <a href="https://stackoverflow.com/questions/24007650/selector-in-swift?rq=1">this post</a> had all the answers, but it doesn't.</p>

<p>I've tried this Dismissable protocol with and without exposing it to <code>@objc</code>:</p>

<pre><code>@objc protocol Dismissable: class {
    weak var dismissalDelegate: DismissalDelegate? {
        get set }
    }
</code></pre>

<p>And I've also tried it with my DismissalDelegate protocol:</p>

<pre><code>@objc protocol DismissalDelegate : class {
    func selectionDidFinish(controller: UIViewController)
}

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

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

<p><strong>EDIT: Final fix</strong></p>

<p>Based on the accepted answer, I added a function to do the dismissal:</p>

<pre><code>func dismiss() {
    dismissalDelegate?.selectionDidFinish(self)
}
</code></pre>

<p>and then called the selector like this:</p>

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