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_CreateGenericHandler 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 handler: 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