Swift Delegate and Optional - ios

Question

I'm working on my first iOS app using swift. I'm trying to load the a value from one viewController into another. I am using a protocol, but I can't get it to execute properly. I have searched around both stack overflow and elsewhere but haven't been able to find an answer that works in my situation.
Here's the VC I'm trying to pull the value from:
protocol AddHelperVCDelegate {
func didFinishAddingHelper(controller: AddHelperViewController)
}
class AddHelperViewController: UIViewController, UITableViewDataSource, UITableViewDelegate, NSFetchedResultsControllerDelegate {
#IBOutlet weak var tableView: UITableView!
let managedObjectContext = (UIApplication.sharedApplication().delegate as AppDelegate).managedObjectContext!
var fetchedResultsController:NSFetchedResultsController = NSFetchedResultsController()
var delegate:AddHelperVCDelegate! = nil
var helperBonus:NSNumber = 0
override func viewDidLoad() {
super.viewDidLoad()
fetchedResultsController = getFetchResultsController()
fetchedResultsController.delegate = self
fetchedResultsController.performFetch(nil)
// Do any additional setup after loading the view.
}
}
And here is where I am trying to move the value (and the view) back to a proceeding VC.
// UITableViewDelegate
func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
var indexPathForRow = tableView.indexPathForSelectedRow()
println("indexPath for selected row is: \(indexPathForRow)")
let thisUser = fetchedResultsController.objectAtIndexPath(indexPath) as UserModel
var cell:UserCell = tableView.dequeueReusableCellWithIdentifier("helperCell") as UserCell
helperBonus = thisUser.effectiveCombat
helperBonus = Int(helperBonus)
println("helperBonus is: \(helperBonus)")
delegate.didFinishAddingHelper(self)
}
If I make the delegate an optional (delegate?.didFinishAddingHelper(self)) then nothing happens. If I do not, I get a crash with the error message:
indexPath for selected row is: Optional(<NSIndexPath: 0xc000000000018016> {length = 2, path = 0 - 3})
helperBonus is: 0
fatal error: unexpectedly found nil while unwrapping an Optional value
Now, I know I'm declaring delegate as nil, but that's the limit to my understanding of what's going on. I need to add the value in the proceeding VC in this function:
func didFinishAddingHelper(controller: AddHelperViewController) {
self.effectiveCombat = Int(controller.helperBonus)
controller.navigationController?.popViewControllerAnimated(true)
}

Answer 1

The crash is happening because AddHelperViewController's delegate property is nil. This is because you aren't setting it.
Wherever you create the AddHelperViewController, set its delegate on the next line:
let addHelperVC = AddHelperViewController()
addHelperVC.delegate = self
Then when you call the delegate property, it will point back to the view controller that created it.
If your AddHelperViewController is created using a storyboard, set delegate in the prepareForSegue(_:sender:) of the method that is about to show the new controller:
override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
if let vc = segue.destinationViewController as? AddHelperViewController {
// If we got here, vc is an AddHelperViewController
vc.delegate = self
}
}

Answer 2

var delegate:AddHelperVCDelegate! = nil
Should be
var delegate:AddHelperVCDelegate?
It is failing because you are using !, which means that you guarantee that, while it can't be initialized during the classes init, it will not be nil by the time you want to use it.
Aaron Brager is absolutely correct when he says you need to set the delegate property.
With your delegate declared as optional (with ?), you can call it only if the object is not nil (ignored otherwise):
delegate?.didFinishAddingHelper(self)
On a side note, you might also consider making the delegate property weak in order to help prevent retain cycles.