Recognize when user close a window (when click on close button)

How can i recognize when user close a window ?

i want to do something before window close.

I use it in a viewcontroller

//initWithNibName

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(windowWillClose:) name:NSWindowWillCloseNotification object:self.view.window];

- (void)windowWillClose:(NSNotification *)notification
    {
        NSWindow *win = [notification object];
        //...
    }