EventHndlr

Tk_CreateEventHandler(3)     Tk Library Procedures    Tk_CreateEventHandler(3)



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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 But-
                                              tonPressMask)  for  which   proc
                                              should be called.

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

       ClientData      clientData   (in)      Arbitrary one-word value to pass
                                              to proc.
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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_Han-
       dleEvent;  this  mechanism  only works in programs that dispatch events
       through Tk_HandleEvent  (or  through  other  Tk  procedures  that  call
       Tk_HandleEvent, such as Tk_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.  Typi-
       cally, 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  associ-
       ated  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  argu-
       ments.   When  a  window is deleted all of its handlers will be deleted
       automatically;  in this case there is no need  to  call  Tk_DeleteEven-
       tHandler.

       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



Tk                                                    Tk_CreateEventHandler(3)