eventhndlr(3Tk)

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 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.  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_EventHandler 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 mutliple 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