Tk_DoOneEvent(3Tk)Tk_DoOneEvent(3Tk)NAME
Tk_DoOneEvent, Tk_MainLoop, Tk_HandleEvent - wait for events and invoke
event handlers
SYNOPSIS
#include <tk.h>
int
Tk_DoOneEvent(flags)Tk_MainLoop()Tk_HandleEvent(eventPtr)ARGUMENTS
int flags (in) This parameter is normally zero. It may
be an OR-ed combination of any of the
following flag bits: TK_X_EVENTS,
TK_FILE_EVENTS, TK_TIMER_EVENTS,
TK_IDLE_EVENTS, TK_ALL_EVENTS, or
TK_DONT_WAIT.
XEvent *eventPtr (in) Pointer to X event to dispatch to relevant
handler(s).
DESCRIPTION
These three procedures are responsible for waiting for events and
dispatching to event handlers created with the procedures
Tk_CreateEventHandler, Tk_CreateFileHandler, Tk_CreateTimerHandler, and
Tk_DoWhenIdle. Tk_DoOneEvent is the key procedure. It waits for a
single event of any sort to occur, invokes the handler(s) for that event,
and then returns. Tk_DoOneEvent first checks for X events and file-
related events; if one is found then it calls the handler(s) for the
event and returns. If there are no X or file events pending, then
Tk_DoOneEvent checks to see if timer callbacks are ready; if so, it
makes a single callback and returns. If no timer callbacks are ready,
Tk_DoOneEvent checks for Tk_DoWhenIdle callbacks; if any are found, it
invokes all of them and returns. Finally, if no events or work have been
found, Tk_DoOneEvent sleeps until a timer, file, or X event occurs; then
it processes the first event found (in the order given above) and
returns. The normal return value is 1 to signify that some event or
callback was processed. If no event or callback is processed (under
various conditions described below), then 0 is returned.
If the flags argument to Tk_DoOneEvent is non-zero then it restricts the
kinds of events that will be processed by Tk_DoOneEvent. Flags may be an
OR-ed combination of any of the following bits:
TK_X_EVENTS - Process X events.
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Tk_DoOneEvent(3Tk)Tk_DoOneEvent(3Tk)
TK_FILE_EVENTS - Process file events.
TK_TIMER_EVENTS - Process timer events.
TK_IDLE_EVENTS - Process Tk_DoWhenIdle callbacks.
TK_ALL_EVENTS - Process all kinds of events: equivalent to OR-
ing together all of the above flags or specifying
none of them.
TK_DONT_WAIT - Don't sleep: process only events that are ready
at the time of the call.
If any of the flags TK_X_EVENTS, TK_FILE_EVENTS, TK_TIMER_EVENTS, or
TK_IDLE_EVENTS is set, then the only events that will be considered are
those for which flags are set. Setting none of these flags is equivalent
to the value TK_ALL_EVENTS, which causes all event types to be processed.
The TK_DONT_WAIT flag causes Tk_DoWhenIdle not to put the process to
sleep: it will check for events but if none are found then it returns
immediately with a return value of 0 to indicate that no work was done.
Tk_DoOneEvent will also return 0 without doing anything if flags is
TK_IDLE_EVENTS and there are no Tk_DoWhenIdle callbacks pending. Lastly,|
Tk_DoOneEvent will return 0 without doing anything if there are no events|
or work found and if there are no files, displays, or timer handlers to |
wait for.
Tk_MainLoop is a procedure that loops repeatedly calling Tk_DoOneEvent.
It returns only when there are no applications left in this process (i.e.
no main windows exist anymore). Most X applications will call
Tk_MainLoop after initialization; the main execution of the application
will consist entirely of callbacks invoked by Tk_DoOneEvent.
Tk_HandleEvent is a lower-level procedure invoked by Tk_DoOneEvent. It
makes callbacks to any event handlers (created by calls to
Tk_CreateEventHandler) that match eventPtr and then returns. In some
cases it may be useful for an application to read events directly from X
and dispatch them by calling Tk_HandleEvent, without going through the
additional mechanism provided by Tk_DoOneEvent.
These procedures may be invoked recursively. For example, it is possible
to invoke Tk_DoOneEvent recursively from a handler called by
Tk_DoOneEvent. This sort of operation is useful in some modal
situations, such as when a notifier has been popped up and an application
wishes to wait for the user to click a button in the notifier before
doing anything else.
KEYWORDS
callback, event, handler, idle, timer
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