Swift - Capture keydown from NSViewController

I was trying to find an answer for swift 3, here is what worked for me:

Swift 3

import Cocoa

// We subclass an NSView

class MainView: NSView {

    // Allow view to receive keypress (remove the purr sound)
    override var acceptsFirstResponder : Bool {
        return true
    }

    // Override the NSView keydown func to read keycode of pressed key
    override func keyDown(with theEvent: NSEvent) {
        Swift.print(theEvent.keyCode)
    }

}

I manage to get it work from subclass of NSWindowController

class MyWindowController: NSWindowController {

    override func keyDown(theEvent: NSEvent) {
        print("keyCode is \(theEvent.keyCode)")
    }
}

UPDATE:

import Cocoa

protocol WindowControllerDelegate {
    func keyDown(aEvent: NSEvent)
}

class WindowController: NSWindowController {

    var delegate: WindowControllerDelegate?

    override func windowDidLoad() {
        super.windowDidLoad()
        delegate = window?.contentViewController as! ViewController
    }
    override func keyDown(theEvent: NSEvent) {
        delegate?.keyDown(theEvent)
    }

}

and ViewController:

class ViewController: NSViewController, WindowControllerDelegate {

    @IBOutlet weak var textField: NSTextField!

    override func viewDidLoad() {
        super.viewDidLoad()

        // Do any additional setup after loading the view.
    }

    override var representedObject: AnyObject? {
        didSet {
        // Update the view, if already loaded.
        }
    }
    override func keyDown(theEvent: NSEvent) {
        textField.stringValue = "key = " + (theEvent.charactersIgnoringModifiers
            ?? "")
        textField.stringValue += "\ncharacter = " + (theEvent.characters ?? "")
        textField.stringValue += "\nmodifier = " + theEvent.modifierFlags.rawValue.description
    }

}

Xcode 8.2.1 • Swift 3.0.2

import Cocoa

class ViewController: NSViewController {

    @IBOutlet var textField: NSTextField!

    override func viewDidLoad() {
        super.viewDidLoad()
        NSEvent.addLocalMonitorForEvents(matching: .flagsChanged) {
            self.flagsChanged(with: $0)
            return $0
        }
        NSEvent.addLocalMonitorForEvents(matching: .keyDown) {
            self.keyDown(with: $0)
            return $0
        }
    }
    override func keyDown(with event: NSEvent) {
        switch event.modifierFlags.intersection(.deviceIndependentFlagsMask) {
        case [.command] where event.characters == "l",
             [.command, .shift] where event.characters == "l":
            print("command-l or command-shift-l")
        default:
            break
        }
        textField.stringValue = "key = " + (event.charactersIgnoringModifiers
            ?? "")
        textField.stringValue += "\ncharacter = " + (event.characters ?? "")
    }
    override func flagsChanged(with event: NSEvent) {
        switch event.modifierFlags.intersection(.deviceIndependentFlagsMask) {
        case [.shift]:
            print("shift key is pressed")
        case [.control]:
            print("control key is pressed")
        case [.option] :
            print("option key is pressed")
        case [.command]:
            print("Command key is pressed")
        case [.control, .shift]:
            print("control-shift keys are pressed")
        case [.option, .shift]:
            print("option-shift keys are pressed")
        case [.command, .shift]:
            print("command-shift keys are pressed")
        case [.control, .option]:
            print("control-option keys are pressed")
        case [.control, .command]:
            print("control-command keys are pressed")
        case [.option, .command]:
            print("option-command keys are pressed")
        case [.shift, .control, .option]:
            print("shift-control-option keys are pressed")
        case [.shift, .control, .command]:
            print("shift-control-command keys are pressed")
        case [.control, .option, .command]:
            print("control-option-command keys are pressed")
        case [.shift, .command, .option]:
            print("shift-command-option keys are pressed")
        case [.shift, .control, .option, .command]:
            print("shift-control-option-command keys are pressed")
        default:
            print("no modifier keys are pressed")
        }
    }
}

---

To get rid of the purr sound when pressing the character keys you need to subclass your view, override the method performKeyEquivalent and return true.

import Cocoa

class View: NSView {
    override func performKeyEquivalent(with event: NSEvent) -> Bool {
        return true
    }
}

Sample Project

Swift4

Just found a solution for the very same problem, Swift4. The idea behind that: if the pressed key was handled by a custom logic, the handler shall return nil, otherwise the (unhandled) event...

class MyViewController: NSViewController {
   override func viewDidLoad() {
      super.viewDidLoad()
      // ...
      NSEvent.addLocalMonitorForEvents(matching: .keyDown) {
         if self.myKeyDown(with: $0) {
            return nil
         } else {
            return $0
         }
      }
   }
   func myKeyDown(with event: NSEvent) -> Bool {
      // handle keyDown only if current window has focus, i.e. is keyWindow
      guard let locWindow = self.view.window,
         NSApplication.shared.keyWindow === locWindow else { return false }
      switch Int( event.keyCode) {
      case kVK_Escape:
         // do what you want to do at "Escape"
         return true
      default: 
         return false
      }
   }
}

And here we are: no Purr / Funk sound when key is pressed...

[Update] Added check of keyWindow. Without this, keyDown() is fired even if another view/window contains the first responder...