On a Mac how to determine a user logout is occuring

I am very new to the Mac platform and Objective-C in g开发者_开发知识库eneral and in my application I would like to know how to determine that a user is logging out and perform some actions prior to this. Any info or pointers for this?

The official way to put the hook at logging in / logging out is described in these Apple documents Customizing Login and Logout and Tech Note 2228. But I'm afraid that the log-out hook was no longer directly supported.

So, the second best way is to run a headless Cocoa app, and receive a notification from the system using NSWorkspace, see the document and the list of available notifications.

To make a headless Cocoa app, you need to set an entry in its Info.plist called LSUIElement, see here. By setting LSUIElement to be yes, the app don't appear in the dock, but perform various operation in the background.

Take a look at Receiving Workspace Notifications in this Workspace Services document.

NSWorkspaceWillPowerOffNotification

Posted when the user has requested a logout or that the machine be powered off.