How to use NSTrackingArea

Answer by Matt Bierner really helped me out; needing to implement -viewWillMoveToWindow: method.

I would also add that you will also need to implement this if you want to handle tracking areas when the view is resized:

- (void)updateTrackingAreas
{
   // remove out-of-date tracking areas and add recomputed ones..
}

in the custom sub-class, to handle the view's changing geometry; this'll be invoked for you automatically.

Apple provides documentation and examples for NSTrackingAreas.

The easiest way to track when a mouse enters or exits a window is by setting a tracking area in the window's contentView. This will however not track the window's toolbar

Just as a quick example, in the custom content view's code:

- (void) viewWillMoveToWindow:(NSWindow *)newWindow {
    // Setup a new tracking area when the view is added to the window.
    NSTrackingArea* trackingArea = [[NSTrackingArea alloc] initWithRect:[self bounds] options: (NSTrackingMouseEnteredAndExited | NSTrackingActiveAlways) owner:self userInfo:nil];
    [self addTrackingArea:trackingArea];
}

- (void) mouseEntered:(NSEvent*)theEvent {
    // Mouse entered tracking area.
}

- (void) mouseExited:(NSEvent*)theEvent {
    // Mouse exited tracking area.
}

You should also implement NSView's updateTrackingAreas method and test the event's tracking area to make sure it is the right one.