I need to get arrow key presses, but keyDown won't call (Swift)

Question

I am trying to build a Mac App which displays images and I want to move on to the next image when I press the right arrow key. I have looked all over stackoverflow and the internet, but just can't seem to get it.

What I tried... I tried to use keyDown(theEvent: NSEvent)but it does not call when I press any keys. I believe this is because it is not in a text field of some kind, but not sure.

What Happens... When i'm testing the program, I press a key (with keyDown function ready to println("Key Pressed")) and I get the OS X reject noise and no println to the console.

I have heard of some people subclassing NSView to override acceptsFirstResponder, but I am new to subclassing so any direction you could point me in would be great. Or if there is a way to do it w/o subclassing NSView that would be great!

Thanks in advance! Sorry for the noobness.

Answer 1

Subclassing is less difficult than it seems.

Short tutorial:

General assumption: keystrokes are going to be received in the view of a NSViewController subclass and to be processed in the view controller class

• Create a new Cocoa Class named MyView as a subclass of NSView

• Replace the contents of the created class with

  import Cocoa
  
  let leftArrowKey = 123
  let rightArrowKey = 124
  
  protocol MyViewDelegate {
    func didPressLeftArrowKey()
    func didPressRightArrowKey()
  }
  
  class MyView: NSView {
  
     var delegate : MyViewDelegate?
  
     override func keyDown(event: NSEvent) {
       let character = Int(event.keyCode)
       switch character {
       case leftArrowKey, rightArrowKey:
         break
       default:
         super.keyDown(event)
       }
     }
  
     override func keyUp(event: NSEvent) {
       let character = Int(event.keyCode)
       switch character {
       case leftArrowKey:
         delegate?.didPressLeftArrowKey()
       case rightArrowKey:
         delegate?.didPressRightArrowKey()
       default:
         super.keyUp(event)
       }
     }
  
      override var acceptsFirstResponder : Bool {
        return true
      }
    } 
  

  • Change the class of the view of the ViewController in Interface Builder to MyView

  • In the ViewController class add the protocol MyViewDelegate- for example

    class ViewController: NSViewController, MyViewDelegate {
    

  • In viewDidLoad() add

    let view = self.view as! MyView
    view.delegate = self
    self.nextResponder = view
    

  • Implement the following delegate methods and add your code to switch the image(s)

    func didPressLeftArrowKey() {
      println("didPressLeftArrowKey")
      // process keystroke left arrow
    }
    
    func didPressRightArrowKey() {
      println("didPressRightArrowKey")
      // process keystroke right arrow
    }
    

The delegate methods are called when the appropriate arrow keys are released