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CentOS 7.0 - man page for tk_creategenerichandler (centos section 3)

Tk_CreateGenericHandler(3)	      Tk Library Procedures	       Tk_CreateGenericHandler(3)

_________________________________________________________________________________________________

NAME
       Tk_CreateGenericHandler, Tk_DeleteGenericHandler - associate procedure callback with all X
       events

SYNOPSIS
       #include <tk.h>

       Tk_CreateGenericHandler(proc, clientData)

       Tk_DeleteGenericHandler(proc, clientData)

ARGUMENTS
       Tk_GenericProc *proc (in)	       Procedure to invoke whenever any X event occurs on
					       any display.

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

DESCRIPTION
       Tk_CreateGenericHandler arranges for proc to be invoked in the future whenever any X event
       occurs.	This mechanism is not intended for dispatching X events on windows managed by  Tk
       (you  should  use  Tk_CreateEventHandler  for  this  purpose).  Tk_CreateGenericHandler is
       intended for other purposes, such as tracing X events, monitoring events  on  windows  not
       owned  by Tk, accessing X-related libraries that were not originally designed for use with
       Tk, and so on.

       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_GenericProc:
	      typedef int Tk_GenericProc(
		  ClientData clientData,
		  XEvent *eventPtr);
       The clientData parameter to proc is a copy of the clientData argument given to  Tk_Create-
       GenericHandler  when  the  callback  was  created.  Typically, clientData points to a data
       structure  containing  application-specific  information  about	how  to  handle   events.
       EventPtr is a pointer to the X event.

       Whenever an X event is processed by Tk_HandleEvent, proc is called.  The return value from
       proc is normally 0.  A non-zero return value indicates that the event is not to be handled
       further; that is, proc has done all processing that is to be allowed for the event.

       If  there  are  multiple generic event handlers, each one is called for each event, in the
       order in which they were established.

       Tk_DeleteGenericHandler may be called to delete a previously-created  generic  event  han-
       dler:   it  deletes  each handler it finds that matches the proc and clientData arguments.
       If no such handler exists, then Tk_DeleteGenericHandler returns	without  doing	anything.
       Although  Tk supports it, it's probably a bad idea to have more than one callback with the
       same proc and clientData arguments.

       Establishing a generic event handler does nothing to ensure that the process will actually
       receive	the  X events that the handler wants to process.  For example, it is the caller's
       responsibility to invoke XSelectInput to select the desired events, if that is necessary.

KEYWORDS
       bind, callback, event, handler

Tk								       Tk_CreateGenericHandler(3)


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