Cannot call "..." with an argument list like "..."

This line:

appDelegate.navigationController.pushViewControllerOnTopOfEverything(controller)

      

        
        
        
      

    

raises this error:

Cannot invoke 'pushViewControllerOnTopOfEverything' with an argument list of type '(VUPickerController!)'

      

        
        
        
      

    

Here's the complete function:

    func onSortTapped() {

    if self.pickerModel == nil {
        self.pickerModel = VUPickerModel.newOrExistingPickerModelForKey(VUPickerModelKeyType.ShowsSort)
    }

    var controller = VUPickerController(model: self.pickerModel) { (selectionChanged) in

        if selectionChanged {
            self.pickerModel?.archiveWithModelKeyType(VUPickerModelKeyType.ShowsSort)

            let userSelections = self.pickerModel!.selectedRows()
            let sectionItem = userSelections![0] as! VUPickerSectionItem
            self.leftGenreBar?.genreName = sectionItem.title
        }
    }

    let appDelegate = UIApplication.sharedApplication().delegate
    appDelegate.navigationController.pushViewControllerOnTopOfEverything(controller)

}

      

        
        
        
      

    

navigationController

is the usual UIViewController

, written in Obj-C, and pushViewControllerOnTopOfEverything

is defined as:

- (void)pushViewControllerOnTopOfEverything:(UIViewController *)viewController;

      

        
        
        
      

    

It is also VUPickerController

subclassed from UIViewController

.

onSortTapped()

was originally written in Obj-C and I am trying to do a simple translation, but I am missing something.

I tried casting for UIViewController

:

appDelegate.navigationController.pushViewControllerOnTopOfEverything(controller as! UIViewController)

      

        
        
        
      

    

but got a similar error:

Cannot invoke 'pushViewControllerOnTopOfEverything' with an argument list of type '(UIViewController)'

      

        
        
        
      

    

EDIT

When I try:

po appDelegate.navigationController

      

        
        
        
      

    

in the debug console:

error: <EXPR>:1:13: error: type of expression is ambiguous without more context

      

        
        
        
      

    

If I just po:

po appDelegate

      

        
        
        
      

    

I get:

Printing description of appDelegate:
Optional(<AppDelegate: 0x7f81a2d1cc40>)

      

        
        
        
      

    

And it navigationController

is the appDelegate property declared in the Obj-C source file appDelegate.h

.