Description
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() macro 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
GtkFileChooserDialog. After a callback finishes, GTK+ will return to the
main loop and await more user input.
Typical main() function for a GTK+ application
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.
Functions
gtk_disable_setlocale ()
void
gtk_disable_setlocale (void);
Prevents gtk_init(), gtk_init_check(), gtk_init_with_args() and
gtk_parse_args() from automatically
calling setlocale (LC_ALL, ""). You would
want to use this function if you wanted to set the locale for
your program to something other than the user’s locale, or if
you wanted to set different values for different locale categories.
Most programs should not need to call this function.
gtk_get_default_language ()
PangoLanguage *
gtk_get_default_language (void);
Returns the PangoLanguage for the default language currently in
effect. (Note that this can change over the life of an
application.) The default language is derived from the current
locale. It determines, for example, whether GTK+ uses the
right-to-left or left-to-right text direction.
This function is equivalent to pango_language_get_default().
See that function for details.
Returns
the default language as a PangoLanguage,
must not be freed.
[transfer none]
gtk_get_locale_direction ()
GtkTextDirection
gtk_get_locale_direction (void);
Get the direction of the current locale. This is the expected
reading direction for text and UI.
This function depends on the current locale being set with
setlocale() and will default to setting the GTK_TEXT_DIR_LTR
direction otherwise. GTK_TEXT_DIR_NONE will never be returned.
GTK+ sets the default text direction according to the locale
during gtk_init(), and you should normally use
gtk_widget_get_direction() or gtk_widget_get_default_direction()
to obtain the current direcion.
This function is only needed rare cases when the locale is
changed after GTK+ has already been initialized. In this case,
you can use it to update the default text direction as follows:
Since: 3.12
gtk_parse_args ()
gboolean
gtk_parse_args (int *argc,
char ***argv);
Parses command line arguments, and initializes global
attributes of GTK+, but does not actually open a connection
to a display. (See gdk_display_open(), gdk_get_display_arg_name())
Any arguments used by GTK+ or GDK are removed from the array and
argc
and argv
are updated accordingly.
There is no need to call this function explicitly if you are using
gtk_init(), or gtk_init_check().
Note that many aspects of GTK+ require a display connection to
function, so this way of initializing GTK+ is really only useful
for specialized use cases.
Returns
TRUE if initialization succeeded, otherwise FALSE
gtk_init ()
void
gtk_init (int *argc,
char ***argv);
Call this function before using any other GTK+ functions in your GUI
applications. It will initialize everything needed to operate the
toolkit and parses some standard command line options.
Although you are expected to pass the argc
, argv
parameters from main() to
this function, it is possible to pass NULL if argv
is not available or
commandline handling is not required.
argc
and argv
are adjusted accordingly so your own code will
never see those standard arguments.
Note that there are some alternative ways to initialize GTK+:
if you are calling gtk_parse_args(), gtk_init_check(),
gtk_init_with_args() or g_option_context_parse() with
the option group returned by gtk_get_option_group(),
you don’t have to call gtk_init().
And if you are using GtkApplication, you don't have to call any of the
initialization functions either; the “startup” handler
does it for you.
This function will terminate your program if it was unable to
initialize the windowing system for some reason. If you want
your program to fall back to a textual interface you want to
call gtk_init_check() instead.
Since 2.18, GTK+ calls signal (SIGPIPE, SIG_IGN)
during initialization, to ignore SIGPIPE signals, since these are
almost never wanted in graphical applications. If you do need to
handle SIGPIPE for some reason, reset the handler after gtk_init(),
but notice that other libraries (e.g. libdbus or gvfs) might do
similar things.
gtk_init_check ()
gboolean
gtk_init_check (int *argc,
char ***argv);
This function does the same work as gtk_init() with only a single
change: It does not terminate the program if the commandline
arguments couldn’t be parsed or the windowing system can’t be
initialized. Instead it returns FALSE on failure.
This way the application can fall back to some other means of
communication with the user - for example a curses or command line
interface.
Note that calling any GTK function or instantiating any GTK type after
this function returns FALSE results in undefined behavior.
Returns
TRUE if the commandline arguments (if any) were valid and
the windowing system has been successfully initialized, FALSE
otherwise
gtk_init_with_args ()
gboolean
gtk_init_with_args (gint *argc,
gchar ***argv,
const gchar *parameter_string,
const GOptionEntry *entries,
const gchar *translation_domain,
GError **error);
This function does the same work as gtk_init_check().
Additionally, it allows you to add your own commandline options,
and it automatically generates nicely formatted
--help output. Note that your program will
be terminated after writing out the help output.
Returns
TRUE if the commandline arguments (if any) were valid and
if the windowing system has been successfully initialized,
FALSE otherwise
Since: 2.6
gtk_events_pending ()
gboolean
gtk_events_pending (void);
Checks if any events are pending.
This can be used to update the UI and invoke timeouts etc.
while doing some time intensive computation.
Updating the UI during a long computation
Returns
TRUE if any events are pending, FALSE otherwise
gtk_main ()
void
gtk_main (void);
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.
gtk_main_level ()
guint
gtk_main_level (void);
Asks for the current nesting level of the main loop.
Returns
the nesting level of the current invocation
of the main loop
gtk_main_quit ()
void
gtk_main_quit (void);
Makes the innermost invocation of the main loop return
when it regains control.
gtk_main_iteration ()
gboolean
gtk_main_iteration (void);
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.
gtk_main_iteration_do ()
gboolean
gtk_main_iteration_do (gboolean blocking);
Runs a single iteration of the mainloop.
If no events are available either return or block depending on
the value of blocking
.
gtk_main_do_event ()
void
gtk_main_do_event (GdkEvent *event);
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.
Then the event is pushed onto 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.
GtkModuleInitFunc ()
void
(*GtkModuleInitFunc) (gint *argc,
gchar ***argv);
Each GTK+ module must have a function gtk_module_init() with this prototype.
This function is called after loading the module.
GtkModuleDisplayInitFunc ()
void
(*GtkModuleDisplayInitFunc) (GdkDisplay *display);
A multihead-aware GTK+ module may have a gtk_module_display_init() function
with this prototype. GTK+ calls this function for each opened display.
Since: 2.2
gtk_true ()
gboolean
gtk_true (void);
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...
gtk_false ()
gboolean
gtk_false (void);
Analogical to gtk_true(), this function does nothing
but always returns FALSE.
gtk_grab_add ()
void
gtk_grab_add (GtkWidget *widget);
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.
If widget
is not sensitive, it is not set as the current
grabbed widget and this function does nothing.
[method]
gtk_grab_get_current ()
GtkWidget *
gtk_grab_get_current (void);
Queries the current grab of the default window group.
Returns
The widget which currently
has the grab or NULL if no grab is active.
[transfer none][nullable]
gtk_grab_remove ()
void
gtk_grab_remove (GtkWidget *widget);
Removes the grab from the given widget.
You have to pair calls to gtk_grab_add() and gtk_grab_remove().
If widget
does not have the grab, this function does nothing.
[method]
gtk_device_grab_add ()
void
gtk_device_grab_add (GtkWidget *widget,
GdkDevice *device,
gboolean block_others);
Adds a GTK+ grab on device
, so all the events on device
and its
associated pointer or keyboard (if any) are delivered to widget
.
If the block_others
parameter is TRUE, any other devices will be
unable to interact with widget
during the grab.
Since: 3.0
gtk_key_snooper_install ()
guint
gtk_key_snooper_install (GtkKeySnoopFunc snooper,
gpointer func_data);
gtk_key_snooper_install has been deprecated since version 3.4 and should not be used in newly-written code.
Key snooping should not be done. Events should
be handled by widgets.
Installs a key snooper function, which will get called on all
key events before delivering them normally.
[skip]
GtkKeySnoopFunc ()
gint
(*GtkKeySnoopFunc) (GtkWidget *grab_widget,
GdkEventKey *event,
gpointer func_data);
Key snooper functions are called before normal event delivery.
They can be used to implement custom key event handling.
Returns
TRUE to stop further processing of event
, FALSE to continue.
gtk_key_snooper_remove ()
void
gtk_key_snooper_remove (guint snooper_handler_id);
gtk_key_snooper_remove has been deprecated since version 3.4 and should not be used in newly-written code.
Key snooping should not be done. Events should
be handled by widgets.
Removes the key snooper function with the given id.
gtk_get_current_event ()
GdkEvent *
gtk_get_current_event (void);
Obtains a copy of the event currently being processed by GTK+.
For example, if you are handling a “clicked” signal,
the current event will be the GdkEventButton that triggered
the ::clicked signal.
Returns
a copy of the current event, or
NULL if there is no current event. The returned event must be
freed with gdk_event_free().
[transfer full][nullable]
gtk_get_current_event_time ()
guint32
gtk_get_current_event_time (void);
If there is a current event and it has a timestamp,
return that timestamp, otherwise return GDK_CURRENT_TIME.
gtk_get_current_event_state ()
gboolean
gtk_get_current_event_state (GdkModifierType *state);
If there is a current event and it has a state field, place
that state field in state
and return TRUE, otherwise return
FALSE.
Returns
TRUE if there was a current event and it
had a state field
gtk_get_current_event_device ()
GdkDevice *
gtk_get_current_event_device (void);
If there is a current event and it has a device, return that
device, otherwise return NULL.
gtk_get_event_widget ()
GtkWidget *
gtk_get_event_widget (GdkEvent *event);
If event
is NULL or the event was not associated with any widget,
returns NULL, otherwise returns the widget that received the event
originally.
Returns
the widget that originally
received event
, or NULL.
[transfer none][nullable]
gtk_propagate_event ()
void
gtk_propagate_event (GtkWidget *widget,
GdkEvent *event);
Sends an event to a widget, propagating the event to parent widgets
if the event remains unhandled.
Events received by GTK+ from GDK normally begin in gtk_main_do_event().
Depending on the type of event, existence of modal dialogs, grabs, etc.,
the event may be propagated; if so, this function is used.
gtk_propagate_event() calls gtk_widget_event() on each widget it
decides to send the event to. So gtk_widget_event() is the lowest-level
function; it simply emits the “event” and possibly an
event-specific signal on a widget. gtk_propagate_event() is a bit
higher-level, and gtk_main_do_event() is the highest level.
All that said, you most likely don’t want to use any of these
functions; synthesizing events is rarely needed. There are almost
certainly better ways to achieve your goals. For example, use
gdk_window_invalidate_rect() or gtk_widget_queue_draw() instead
of making up expose events.