SetCtlAction
ProcPtr actionProc ; address of Pascal-type procedure SetCtlAction sets the default procedure to be called repeatedly when a control is being tracked. It is only needed if you expect to call TrackControl with (-1) as the final parameter.
theControl is a handle leading to a variable-length ControlRecord structure. It specifies which control to modify.
actionProc is a ProcPtr (pointer to a Pascal-type function). The value passed
here is stored into (* theControl )->contrlAction.
Notes: See TrackControl for the particulars of how to define the actionProc routine. The routine will be called repeatedly while the mouse button is
pressed during a TrackControl call, but only if the final parameter of that call is -1.
There is little reason to set a default action procedure, since you can
specify custom action-handling at the time of the call to TrackControl. Also, you may need to create two such procedures-one to handle indicators
and one to handle other types of controls-then switch back and forth,
making sure that the correct default procedure is in place. In most cases,
it's best to leave the contrlAction field set to NIL.