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To allow another call-back function to be called.




Usually if a window invokes a call-back function (in response to a menu, say) most of the standard controls are inhibited from raising further call-backs. This action is normally desirable as it prevents unfortunate complications if the user's mouse 'bounces' on a button.

The subroutine PERMIT_ANOTHER_CALLBACK@ allows a call-back function to permit an additional call-back. This routine will only permit one additional call-back, but it can be called as many times as desired, each time enabling a further call-back. When using this routine it is assumed that a call will also be made to a routine such as TEMPORARY_YIELD@ to permit the processing of further messages.


Many programs that seem to require this facility may be presenting the user with a non-standard interface and should be re-structured. For example, suppose a window offers a menu item which will start a lengthy calculation which the user may wish to abort. The usual way to handle this is to display a small additional window with a Cancel button and possibly a progress bar. Since this additional window is distinct from the window which contained the original menu item, there is no need to call the above routine.

See also




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