NAME

       Tk_CreateEventHandler,  Tk_DeleteEventHandler  -  associate  procedure  callback with an X
       event

SYNOPSIS

       #include <tk.h>

       Tk_CreateEventHandler(tkwin, mask, proc, clientData)

       Tk_DeleteEventHandler(tkwin, mask, proc, clientData)

ARGUMENTS

       Tk_Window tkwin (in)                   Token for window in which events may occur.

       unsigned long mask (in)                Bit-mask of events (such  as  ButtonPressMask)  for
                                              which proc should be called.

       Tk_EventProc *proc (in)                Procedure  to  invoke  whenever  an  event  in mask
                                              occurs in the window given by tkwin.

       ClientData clientData (in)             Arbitrary one-word value to pass to proc.
_________________________________________________________________________________________________

DESCRIPTION

       Tk_CreateEventHandler arranges for proc to be invoked in the future whenever  one  of  the
       event  types  specified  by mask occurs in the window specified by tkwin.  The callback to
       proc will be made by Tk_HandleEvent; this mechanism only works in programs  that  dispatch
       events  through  Tk_HandleEvent  (or through other Tk procedures that call Tk_HandleEvent,
       such as Tcl_DoOneEvent or Tk_MainLoop).

       Proc should have arguments and result that match the type Tk_EventProc:
              typedef void Tk_EventProc(
                      ClientData clientData,
                      XEvent *eventPtr);
       The clientData  parameter  to  proc  is  a  copy  of  the  clientData  argument  given  to
       Tk_CreateEventHandler  when  the  callback was created.  Typically, clientData points to a
       data structure containing application-specific information about the window in  which  the
       event  occurred.   EventPtr  is  a  pointer  to the X event, which will be one of the ones
       specified in the mask argument to Tk_CreateEventHandler.

       Tk_DeleteEventHandler may be called to delete  a  previously-created  event  handler:   it
       deletes  the  first  handler  it finds that is associated with tkwin and matches the mask,
       proc, and clientData arguments.  If no such handler exists,  then  Tk_HandleEvent  returns
       without  doing  anything.   Although Tk supports it, it's probably a bad idea to have more
       than one callback with the same mask, proc, and clientData arguments.  When  a  window  is
       deleted  all of its handlers will be deleted automatically;  in this case there is no need
       to call Tk_DeleteEventHandler.

       If multiple handlers are declared for the same type of X event on the  same  window,  then
       the handlers will be invoked in the order they were created.

KEYWORDS

       bind, callback, event, handler