Tk_CreateEventHandler (3)
associate procedure callback with an X event
SYNOPSIS
#include <tk.h>
Tk_CreateEventHandler(tkwin, mask, proc, clientData)
Tk_DeleteEventHandler(tkwin, mask, proc, clientData)
ARGUMENTS
"unsigned long" clientData
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 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
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