swift - Cocoa Listen to Keyboard command+up Event -

i working on macos app , handle local hotkey event (command + arrow key) in nsviewcontroller.

here's how swift:

override func keydown(with event: nsevent) {      let modifierkeys = event.modifierflags.intersection(.deviceindependentflagsmask);     let hascommand = modifierkeys == .command;      switch int(event.keycode) {     case kvk_uparrow hascommand:         print("command up");         break;     case kvk_ansi_b hascommand:         print("command b");         break;     default:         break;     } } 

when build , press command+up in view, console shows nothing. when press command+b, "command b" logged out.

so why isn't working command+up? how should achieve this?

i've found solution:

self.keymonitor = nsevent.addlocalmonitorforevents(matching: nseventmask.keydown, handler: { (event) -> nsevent? in      if (event.modifierflags.contains(.command)){         if (int(event.keycode) == kvk_uparrow){             print("command up");             return nil;         }     }      return event;  }); 

the key point interrupt keydown event , prevent being dispatched returning nil