You must set #Com_Owner.avNotifyDeactivation to TRUE if you want to use it.
The uQueryCanDeactivate method may be invoked several times by a single user click, so it is important to reset #pty_NeedsSaving in the routine, so that subsequent invokes do not check with the user again.
There are warnings in the feature help about using method uQueryCanDeactivate and property avNotifyDeactivation in version epc831 of the Framework. These warning can be ignored.
This method can be useful when dealing with objects that don't signal when they have changed. By using this method you can compare a snapshot of the object's current status with its as-loaded status, just at the point the user has finished with the command handler. (Rather than checking for changes every second).
In VLF-WIN, if Framework locks seem to be released automatically after a number of minutes, check that the Framework's autosave interval is set to zero.