events.m

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification {
  [NSEvent addLocalMonitorForEventsMatchingMask: (NSKeyDownMask | NSKeyUpMask | NSFlagsChangedMask)
                                        handler: ^(NSEvent *event) {
    NSEvent *result = event;
                                          
    int flags = [event modifierFlags];
    int cmdDown = !!(flags & NSCommandKeyMask);
    int shiftDown = !!(flags & NSShiftKeyMask);
    int ctrlDown = !!(flags & NSControlKeyMask);
    int altDown = !!(flags & NSAlternateKeyMask);
    switch ([event type]) {
      case NSKeyDown: {
        unichar c = [[event charactersIgnoringModifiers] characterAtIndex:0];
        printf("KEYDOWN Key: %d, Cmd: %d, Shift: %d, Ctrl: %d, Alt: %d\n", c, cmdDown, shiftDown, ctrlDown, altDown);
        result = nil;
      } break;
      case NSKeyUp: {
        unichar c = [[event charactersIgnoringModifiers] characterAtIndex:0];
        printf("KEYUP   Key: %d, Cmd: %d, Shift: %d, Ctrl: %d, Alt: %d\n", c, cmdDown, shiftDown, ctrlDown, altDown);
        result = nil;
      } break;
      case NSFlagsChanged: {
        printf("FLAGS Cmd: %d, Shift: %d, Ctrl: %d, Alt: %d\n", cmdDown, shiftDown, ctrlDown, altDown);
      } break;
      default:
        break;
    }
    return result;
  }];
}