I have a window (in Cocoa) and I need to be able to tell when it is hidden/shown, is minimized/unminimized, and looses/gains focus. Strangely, I can't seem to find any documentation that says how to do this.

You can observe the relevant notifications (listed in the section at the bottom of the NSWindow docs), or you can subclass the window and override the relevant methods (e.g. becomeKeyWindow).

Thank you. And I've just discovered the wonderful world of window delegates.

What's the difference though between a window becoming the key window and a window becoming the main window?