Add completion handler to presentViewControllerAsSheet(NSViewController)?

Question

I am attempting to present a sheet configuration view (AddSoundEffect) for my main window/view controller (I'm using storyboards), and when the configuration view controller is dismissed, take the values entered in the AddSoundEffect view and pass that back to the main view. My current code in the main view controller:

presentViewControllerAsSheet(self.storyboard!.instantiateControllerWithIdentifier("AddSoundEffect") as! AddSoundViewController

And in the AddSoundViewController.swift file, the code to dismiss it is:

self.dismissViewController(self)

To pass the data, I have a class-independent tuple that I save data to. How do I add a completion handler to presentViewControllerAsSheet, and (optionally) is there a better way to pass the data between view controllers?

Setup: Xcode version 6.4, OS X 10.10.4

Answer 1

Delegation pattern is the easiest way for you.

// Replace this with your tuple or whatever data represents your sound effect
struct SoundEffect {}

protocol AddSoundViewControllerDelegate: class {
  func soundViewController(controller: AddSoundViewController, didAddSoundEffect: SoundEffect)
}

//
// Let's say this controller is a modal view controller for adding new sound effects
//
class AddSoundViewController: UIViewController {
  weak var delegate: AddSoundViewControllerDelegate?

  func done(sender: AnyObject) {
    // Dummy sound effect info, replace it with your own data
    let soundEffect = SoundEffect()

    //
    // Call it whenever you would like to inform presenting view controller
    // about added sound effect (in case of Done, Add, ... button tapped, do not call it
    // when user taps on Cancel to just dismiss AddSoundViewController)
    //
    self.delegate?.soundViewController(self, didAddSoundEffect: soundEffect)

    // Dismiss self
    self.dismissViewControllerAnimated(true, completion: {})
  }
}

//
// Let's say this controller is main view controller, which contains list of all sound effects,
// with button to add new sound effect via AddSoundViewController
//
class SoundEffectsViewController: UIViewController, AddSoundViewControllerDelegate {
  func presentAddSoundEffectController(sender: AnyObject) {
    if let addSoundController = self.storyboard?.instantiateViewControllerWithIdentifier("AddSoundEffect") as? AddSoundViewController {
      addSoundController.delegate = self
      self.presentViewController(addSoundController, animated: true, completion: {})
    }
  }

  func soundViewController(controller: AddSoundViewController, didAddSoundEffect: SoundEffect) {
    // This method is called only when new sound effect is added
  }
}

Another way is to use closures:

// Replace this with your tuple or whatever data represents your sound effect
struct SoundEffect {}

//
// Let's say this controller is a modal view controller for adding new sound effects
//
class AddSoundViewController: UIViewController {
  var completionHandler: ((SoundEffect) -> ())?

  func done(sender: AnyObject) {
    // Dummy sound effect info, replace it with your own data
    let soundEffect = SoundEffect()

    //
    // Call it whenever you would like to inform presenting view controller
    // about added sound effect (in case of Done, Add, ... button tapped, do not call it
    // when user taps on Cancel to just dismiss AddSoundViewController)
    //
    self.completionHandler?(soundEffect)

    // Dismiss self
    self.dismissViewControllerAnimated(true, completion: {})
  }
}

//
// Let's say this controller is main view controller, which contains list of all sound effects,
// with button to add new sound effect via AddSoundViewController
//
class SoundEffectsViewController: UIViewController {
  func presentAddSoundEffectController(sender: AnyObject) {
    if let addSoundController = self.storyboard?.instantiateViewControllerWithIdentifier("AddSoundEffect") as? AddSoundViewController {
      addSoundController.completionHandler = { [weak self] (soundEffect) -> () in
        // Called when new sound effect is added
      }
      self.presentViewController(addSoundController, animated: true, completion: {})
    }
  }
}

Or many other ways like sending notification, ... Whatever suits your needs. But delegation pattern or closures is the best way to go in this specific case.

---

I missed that your question is about NSViewController. This example is for iOS, but same pattern can be used on OS X without any issues.

Answer 2

The easiest way to detect sheet opening or closing is to use the Sheet Notifications:

class ViewController: NSViewController, NSWindowDelegate {

    override func viewDidLoad(){
        NSApplication.sharedApplication().windows.first?.delegate = self
    }
    func windowDidEndSheet(notification: NSNotification) {

    }
    func windowWillBeginSheet(notification: NSNotification) {

    }
}