通过NSNotification 获得用户信息

The user information dictionary associated with the receiver. (read-only)

May be nil.

The user information dictionary stores any additional objects that objects receiving the notification might use.

For example, in the Application Kit, NSControl objects post the NSControlTextDidChangeNotification whenever the field editor (an NSText object) changes text inside the NSControl. This notification provides the NSControl object as the notification's associated object. In order to provide access to the field editor, the NSControl object posting the notification adds the field editor to the notification's user information dictionary. Objects receiving the notification can access the field editor and the NSControl object posting the notification as follows: