How to intercept toggling fullscreen mode - xcode

Question

I'm creating Mac OS plugin(bundle) for Unity3D. How can I intercept entering cmd-f combination (toggling full screen mode)? I can't create my own window, I can only use default (mainWindow). I've tried to use NSNotificationCenter, but I need to stop event, I don't need just a notification. I've tried to create NSResponder and add it to capture input events, but something don't work. Any ideas how to do it?
NSWindow* window = [[NSApplication sharedApplication] mainWindow];
NSView* view = [window contentView];
NSResponder* oldresp = [view nextResponder];
MyResponder* myres = [MyResponder alloc];
[myres retain];
[view setNextResponder:myres];
and
#interface MyResponder : NSResponder
{
}
- (void)keyDown:(NSEvent *)theEvent;
#end
#implementation MyResponder
- (void)keyDown:(NSEvent *)theEvent
{
NSLog(#"%#",#"!KeyDown Event");
NSString *theArrow = [theEvent charactersIgnoringModifiers];
unichar keyChar = 0;
if ( [theArrow length] == 1 )
{
keyChar = [theArrow characterAtIndex:0];
if ( keyChar == NSModeSwitchFunctionKey )
{
NSLog(#"%#",#"!!!___!!! GOT NSModeSwitchFunctionKey !!!");
return;
}
NSLog(#"%# %d",#"! Key:",keyChar);
}
[super keyDown:theEvent];
}
#end

Answer 1

One solution is to check constantly if the user has switched to fullscreen mode, and if he has, toggle fullscreen off from your program. This may cause some brief lag or graphics sketchiness momentarily, but it should work.
function Update ()
{
if (Screen.fullScreen) {
Screen.fullScreen = false;
}
}
Im not sure of a way to intercept the key press and ignore the command before the program switches though.
See this related post on unity answers about dealing with this on windows:
http://answers.unity3d.com/questions/544183/block-or-override-alt-enter-fullscreen.html