swift: Calling a function in another file - swift

Question

I would like to call functions residing in other files. In my given example I received no syntax errors, and the app runs. When I click the IBAction, the App crashes. I have no idea why. I am using Xcode 6.4 and coding for OS X
please advise.
// FileUtilties.swift
import Foundation
import Cocoa
class FileUtilities: NSObject, NSAlertDelegate {
var fileList : String!
func listFilesFromDocumentsFolder() -> [String]
{
var theError = NSErrorPointer()
let dirs = NSSearchPathForDirectoriesInDomains(NSSearchPathDirectory.DocumentDirectory, NSSearchPathDomainMask.AllDomainsMask, true) as? [String]
if dirs != nil {
let dir = dirs![0]
let fileList = NSFileManager.defaultManager().contentsOfDirectoryAtPath(dir, error: theError)
return fileList as! [String] // edit: added ! for Swift 1.2 compatibitily
}
else{
let fileList : String!
}
return [fileList]
}
// Alert popup Window
func IdialogOKCancel(myQuestion: String, myText: String) -> Bool {
let myPopup: NSAlert = NSAlert()
myPopup.messageText = myQuestion
myPopup.informativeText = myText
myPopup.alertStyle = NSAlertStyle.WarningAlertStyle
myPopup.addButtonWithTitle("OK")
myPopup.addButtonWithTitle("Cancel")
let res = myPopup.runModal()
if res == NSAlertFirstButtonReturn {
return true
}
return false
}
}
// ViewController.swift
import Cocoa
class ViewController: NSViewController, NSTableViewDataSource, NSTableViewDelegate {
// setsup outlet to add data to ListViewer
#IBOutlet weak var ListViewer: NSScrollView!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
}
override var representedObject: AnyObject? {
didSet {
// Update the view, if already loaded.
}
}
#IBAction func AddButtonClicked(sender: AnyObject) {
var rtnText: String = "this is the text "
var rtn: Bool = false
let instance = FileUtilities()
rtn = instance.IdialogOKCancel("Ok?", myText: rtnText)
}
}