Anyways after trying out so many options and digging into the NSWorkspace i have found way through which we can achieve this their is notification
"NSWorkspaceActiveSpaceDidChangeNotification"
Apple doc says "Posted when a Spaces change has occurred." so by using we can register for it. along with this we need to use the NSWindow's property "isOnActiveSpace" , so by this we can detect when application enters full screen mode and exits from it.