Main loop and Events
Library initialization, main event loop, and events
Before using GTK+, you need to initialize it; initialization connects
to the window system display, and parses some standard command line
arguments. The gtk_init() function initializes GTK+. gtk_init() exits
the application if errors occur; to avoid this, use gtk_init_check().
gtk_init_check() allows you to recover from a failed GTK+
initialization - you might start up your application in text mode instead.
Like all GUI toolkits, GTK+ uses an event-driven programming
model. When the user is doing nothing, GTK+ sits in the
main loop and waits for input. If the user
performs some action - say, a mouse click - then the main loop "wakes
up" and delivers an event to GTK+. GTK+ forwards the event to one or
more widgets.
When widgets receive an event, they frequently emit one or more
signals. Signals notify your program that
"something interesting happened" by invoking functions you've
connected to the signal with g_signal_connect(). Functions connected
to a signal are often termed callbacks.
When your callbacks are invoked, you would typically take some action
- for example, when an Open button is clicked you might display a
#GtkFileSelectionDialog. After a callback finishes, GTK+ will return
to the main loop and await more user input.
Typical <function>main</function> function for a GTK+ application
int
main (int argc, char **argv)
{
/* Initialize i18n support */
gtk_set_locale ();
/* Initialize the widget set */
gtk_init (&argc, &argv);
/* Create the main window */
mainwin = gtk_window_new (GTK_WINDOW_TOPLEVEL);
/* Set up our GUI elements */
...
/* Show the application window */
gtk_widget_show_all (mainwin);
/* Enter the main event loop, and wait for user interaction */
gtk_main ();
/* The user lost interest */
return 0;
}
It's OK to use the GLib main loop directly instead of gtk_main(),
though it involves slightly more typing. See #GMainLoop in the GLib
documentation.
See the GLib manual, especially #GMainLoop and signal-related
functions such as g_signal_connect().
@Returns:
@Returns:
@argc:
@argv:
@argc:
@argv:
@Returns:
Terminates the program and returns the given exit code to the caller.
This function will shut down the GUI and free all resources allocated
for GTK+.
@error_code: Return value to pass to the caller. This is dependend on the
target system but at least on Unix systems %0 means
success.
Checks if any events are pending. This can be used to update the GUI
and invoke timeouts etc. while doing some time intensive computation.
Updating the GUI during a long computation.
/* computation going on */
...
while (gtk_events_pending ())
gtk_main_iteration ();
...
/* computation continued */
@Returns: %TRUE if any events are pending, %FALSE otherwise.
Runs the main loop until gtk_main_quit() is called. You can nest calls to
gtk_main(). In that case gtk_main_quit() will make the innermost invocation
of the main loop return.
Asks for the current nesting level of the main loop. This can be useful
when calling gtk_quit_add().
@Returns: the nesting level of the current invocation of the main loop.
Makes the innermost invocation of the main loop return when it regains
control.
Runs a single iteration of the mainloop. If no events are waiting to be
processed GTK+ will block until the next event is noticed. If you don't
want to block look at gtk_main_iteration_do() or check if any events are
pending with gtk_events_pending() first.
@Returns: %TRUE if gtk_main_quit() has been called for the innermost mainloop.
Runs a single iteration of the mainloop. If no events are available either
return or block dependent on the value of @blocking.
@blocking: %TRUE if you want GTK+ to block if no events are pending.
@Returns: %TRUE if gtk_main_quit() has been called for the innermost mainloop.
Processes a single GDK event. This is public only to allow filtering of events
between GDK and GTK+. You will not usually need to call this function directly.
While you should not call this function directly, you might want to know
how exactly events are handled. So here is what this function does with
the event:
Compress enter/leave notify events. If the event passed build an
enter/leave pair together with the next event (peeked from GDK)
both events are thrown away. This is to avoid a backlog of (de-)highlighting
widgets crossed by the pointer.
Find the widget which got the event. If the widget can't be determined
the event is thrown away unless it belongs to a INCR transaction. In that
case it is passed to gtk_selection_incr_event().
Then the event is passed on a stack so you can query the currently handled
event with gtk_get_current_event().
The event is sent to a widget. If a grab is active all events for
widgets that are not in the contained in the grab widget are sent to the
latter with a few exceptions:
Deletion and destruction events are still sent to the event widget for
obvious reasons.
Events which directly relate to the visual representation of the event
widget.
Leave events are delivered to the event widget if there was an enter
event delivered to it before without the paired leave event.
Drag events are not redirected because it is unclear what the semantics
of that would be.
Another point of interest might be that all key events are first passed
through the key snooper functions if there are any. Read the description
of gtk_key_snooper_install() if you need this feature.
After finishing the delivery the event is popped from the event stack.
@event: An event to process (normally) passed by GDK.
Each GTK+ module must have a function gtk_module_init() with this prototype.
This function is called after loading the module with the @argc and @argv
cleaned from any arguments that GTK+ handles itself.
@argc: Pointer to the number of arguments remaining after gtk_init().
@argv: Points to the argument vector.
@display:
All this function does it to return %TRUE. This can be useful for example
if you want to inhibit the deletion of a window. Of course you should
not do this as the user expects a reaction from clicking the close
icon of the window...
A persistent window
##include <gtk/gtk.h>
int
main (int argc, char **argv)
{
GtkWidget *win, *but;
gtk_init( &argc, &argv );
win = gtk_window_new (GTK_WINDOW_TOPLEVEL);
g_signal_connect (GTK_OBJECT(win), "delete-event",
G_CALLBACK (gtk_true), NULL);
g_signal_connect (GTK_OBJECT(win), "destroy",
G_CALLBACK (gtk_main_quit), NULL);
but = gtk_button_new_with_label ("Close yourself. I mean it!");
g_signal_connect_swapped (GTK_OBJECT (but), "clicked",
G_CALLBACK (gtk_object_destroy), (gpointer) win);
gtk_container_add (GTK_CONTAINER (win), but);
gtk_widget_show_all (win);
gtk_main ();
return 0;
}
@Returns: %TRUE
Analogical to gtk_true() this function does nothing
but always returns %FALSE.
@Returns: %FALSE
Makes @widget the current grabbed widget. This means that interaction with
other widgets in the same application is blocked and mouse as well as
keyboard events are delivered to this widget.
@widget: The widget that grabs keyboard and pointer events.
Queries the current grab.
@Returns: The widget which currently has the grab or %NULL if no grab is active.
Removes the grab from the given widget. You have to pair calls to gtk_grab_add()
and gtk_grab_remove().
@widget: The widget which gives up the grab.
Registers a function to be called when the mainloop is started.
@function: Function to invoke when gtk_main() is called next.
@data: Data to pass to that function.
Trigger destruction of @object in case the mainloop at level @main_level
is quit.
@main_level: Level of the mainloop which shall trigger the destruction.
@object: Object to be destroyed.
Registers a function to be called when an instance of the mainloop is left.
@main_level: Level at which termination the function shall be called. You
can pass 0 here to have the function run at the termination of the current
mainloop.
@function: The function to call. This should return 0 to be removed from the
list of quit handlers. Otherwise the function might be called again.
@data: Pointer to pass when calling @function.
@Returns: A handle for this quit handler (you need this for gtk_quit_remove())
or 0 if you passed a %NULL pointer in @function.
Registers a function to be called when an instance of the mainloop is left.
In comparison to gtk_quit_add() this function adds the possibility to
pass a marshaller and a function to be called when the quit handler is freed.
The former can be used to run interpreted code instead of a compiled function
while the latter can be used to free the information stored in @data (while
you can do this in @function as well)... So this function will mostly be
used by GTK+ wrappers for languages other than C.
@main_level: Level at which termination the function shall be called. You
can pass 0 here to have the function run at the termination of the current
mainloop.
@function: The function to call. This should return 0 to be removed from the
list of quit handlers. Otherwise the function might be called again.
@marshal: The marshaller to be used. If this is non-%NULL, @function is
ignored.
@data: Pointer to pass when calling @function.
@destroy: Function to call to destruct @data. Gets @data as argument.
@Returns: A handle for this quit handler (you need this for gtk_quit_remove())
or 0 if you passed a %NULL pointer in @function.
Removes a quit handler by it's identifier.
@quit_handler_id: Identifier for the handler returned when installing it.
Removes a quit handler identified by it's @data field.
@data: The pointer passed as @data to gtk_quit_add() or gtk_quit_add_full().
Registers a function to be called periodically. The function will be called
repeatedly after @interval milliseconds until it returns %FALSE at which
point the timeout is destroyed and will not be called again.
@interval: The time between calls to the function, in milliseconds
(1/1000ths of a second.)
@function: The function to call periodically.
@marshal: The marshaller to use instead of the function (if non-%NULL).
@data: The data to pass to the function.
@destroy: Function to call when the timeout is destroyed or %NULL.
@Returns: A unique id for the event source.
Registers a function to be called periodically. The function will be called
repeatedly after @interval milliseconds until it returns %FALSE at which
point the timeout is destroyed and will not be called again.
@interval: The time between calls to the function, in milliseconds
(1/1000ths of a second.)
@function: The function to call periodically.
@data: The data to pass to the function.
@Returns: A unique id for the event source.
Removes the given timeout destroying all information about it.
@timeout_handler_id: The identifier returned when installing the timeout.
Causes the mainloop to call the given function whenever no events with
higher priority are to be processed. The default priority is
%GTK_PRIORITY_DEFAULT, which is rather low.
@function: The function to call.
@data: The information to pass to the function.
@Returns: a unique handle for this registration.
Like gtk_idle_add() this function allows you to have a function called
when the event loop is idle. The difference is that you can give a
priority different from %GTK_PRIORITY_DEFAULT to the idle function.
@priority: The priority which should not be above %G_PRIORITY_HIGH_IDLE.
Note that you will interfere with GTK+ if you use a priority above
%GTK_PRIORITY_RESIZE.
@function: The function to call.
@data: Data to pass to that function.
@Returns: A unique id for the event source.
Like gtk_idle_add() this function allows you to have a function called
when the event loop is idle. The difference is that you can give a
priority different from %GTK_PRIORITY_DEFAULT to the idle function.
@priority: The priority which should not be above %G_PRIORITY_HIGH_IDLE.
Note that you will interfere with GTK+ if you use a priority above
%GTK_PRIORITY_RESIZE.
@function: The function to call.
@marshal: The marshaller to use instead of the function (if non-%NULL).
@data: Data to pass to that function.
@destroy: Function to call when the timeout is destroyed or %NULL.
@Returns: A unique id for the event source.
Removes the idle function with the given id.
@idle_handler_id: Identifies the idle function to remove.
Removes the idle function identified by the user data.
@data: remove the idle function which was registered with this user data.
Registers a function to be called when a condition becomes true
on a file descriptor.
@source: a file descriptor.
@condition: the condition.
@function: The function to call.
@marshal: The marshaller to use instead of the function (if non-%NULL).
@data: callback data passed to @function.
@destroy: callback function to call with @data when the input
handler is removed, or %NULL.
@Returns: A unique id for the event source; to be used with gtk_input_remove().
Removes the function with the given id.
@input_handler_id: Identifies the function to remove.
Use this priority for redrawing related stuff. It is used internally by
GTK+ to do pending redraws. This priority is lower than %GTK_PRIORITY_RESIZE
to avoid redrawing a widget just before resizing (and therefore redrawing
it again).
This macro is deprecated. You should use %GDK_PRIORITY_REDRAW instead.
Use this priority for resizing related stuff. It is used internally by
GTK+ to compute the sizes of widgets. This priority is higher than
%GTK_PRIORITY_REDRAW to avoid resizing a widget which was just redrawn.
Use this for high priority timeouts. This priority is never used inside
GTK+ so everything running at this priority will be running before anything
inside the toolkit.
This macro is deprecated. You should use %G_PRIORITY_HIGH instead.
This priority is for GTK+ internal stuff. Don't use it in your applications.
Default priority for idle functions.
This macro is deprecated. You should use %G_PRIORITY_DEFAULT_IDLE instead.
Priority for very unimportant background tasks.
This macro is deprecated. You should use %G_PRIORITY_LOW instead.
Installs a key snooper function, which will get called on all key events
before delivering them normally.
@snooper: a #GtkKeySnoopFunc.
@func_data: data to pass to @snooper.
@Returns: a unique id for this key snooper for use with gtk_key_snooper_remove().
Key snooper functions are called before normal event delivery.
They can be used to implement custom key event handling.
@grab_widget: the widget to which the event will be delivered.
@event: the key event.
@func_data: the @func_data supplied to gtk_key_snooper_install().
@Returns: %TRUE to stop further processing of @event, %FALSE to continue.
Removes the key snooper function with the given id.
@snooper_handler_id: Identifies the key snooper to remove.
@Returns:
@Returns:
@state:
@Returns:
@event:
@Returns:
@widget:
@event: