gtk2/docs/reference/gtk/tmpl/gtkmain.sgml

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<!-- ##### SECTION Title ##### -->
Main loop and Events
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<!-- ##### SECTION Short_Description ##### -->
Library initialization, main event loop, and events
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<!-- ##### SECTION Long_Description ##### -->
<para>
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.
</para>
<para>
Like all GUI toolkits, GTK+ uses an event-driven programming
model. When the user is doing nothing, GTK+ sits in the
<firstterm>main loop</firstterm> 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.
</para>
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<para>
When widgets receive an event, they frequently emit one or more
<firstterm>signals</firstterm>. 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 <firstterm>callbacks</firstterm>.
</para>
<para>
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.
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</para>
<example>
<title>Typical <function>main</function> function for a GTK+ application</title>
<programlisting>
int
main (int argc, char **argv)
{
/* Initialize i18n support */
gtk_set_locale (<!>);
/* Initialize the widget set */
gtk_init (&amp;argc, &amp;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;
}
</programlisting>
</example>
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<para>
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.
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</para>
<!-- ##### SECTION See_Also ##### -->
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<para>
See the GLib manual, especially #GMainLoop and signal-related
functions such as g_signal_connect().
</para>
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<!-- ##### FUNCTION gtk_set_locale ##### -->
<para>
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</para>
@Returns:
<!-- ##### FUNCTION gtk_disable_setlocale ##### -->
<para>
</para>
<!-- ##### FUNCTION gtk_get_default_language ##### -->
<para>
</para>
@Returns:
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<!-- ##### FUNCTION gtk_init ##### -->
<para>
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. <parameter>argc</parameter> and
<parameter>argv</parameter> are adjusted accordingly so your own code will
never see those standard arguments.
</para>
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<note>
<para>
This function will terminate your program if it was unable to initialize
the GUI for some reason. If you want your program to fall back to a
textual interface you want to call gtk_init_check() instead.
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</para>
</note>
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@argc: Address of the <parameter>argc</parameter> parameter of your
<function>main</function> function. Changed if any arguments were
handled.
@argv: Address of the <parameter>argv</parameter> parameter of
<function>main()</function>. Any parameters understood by gtk_init()
are stripped before return.
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<!-- ##### FUNCTION gtk_init_check ##### -->
<para>
This function does the same work as gtk_init() with only
a single change: It does not terminate the program if the GUI can't be
initialized. Instead it returns %FALSE on failure.
</para>
<para>
This way the application can fall back to some other means of communication
with the user - for example a curses or command line interface.
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</para>
@argc: A reference to the <parameter>argc</parameter> of the
<function>main()</function> function.
@argv: A reference to the <parameter>argv</parameter> of the
<function>main()</function> function.
@Returns: %TRUE if the GUI has been successfully initialized,
%FALSE otherwise.
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<!-- ##### FUNCTION gtk_exit ##### -->
<para>
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+.
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</para>
@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.
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<!-- ##### FUNCTION gtk_events_pending ##### -->
<para>
Checks if any events are pending. This can be used to update the GUI
and invoke timeouts etc. while doing some time intensive computation.
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</para>
<example>
<title>Updating the GUI during a long computation.</title>
<programlisting>
/* computation going on */
...
while (gtk_events_pending (<!>))
gtk_main_iteration (<!>);
...
/* computation continued */
</programlisting>
</example>
@Returns: %TRUE if any events are pending, %FALSE otherwise.
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<!-- ##### FUNCTION gtk_main ##### -->
<para>
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.
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</para>
<!-- ##### FUNCTION gtk_main_level ##### -->
<para>
Asks for the current nesting level of the main loop. This can be useful
when calling gtk_quit_add().
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</para>
@Returns: the nesting level of the current invocation of the main loop.
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<!-- ##### FUNCTION gtk_main_quit ##### -->
<para>
Makes the innermost invocation of the main loop return when it regains
control.
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</para>
<!-- ##### FUNCTION gtk_main_iteration ##### -->
<para>
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.
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</para>
@Returns: %TRUE if gtk_main_quit() has been called for the innermost mainloop.
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<!-- ##### FUNCTION gtk_main_iteration_do ##### -->
<para>
Runs a single iteration of the mainloop. If no events are available either
return or block dependent on the value of @blocking.
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</para>
@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.
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<!-- ##### FUNCTION gtk_main_do_event ##### -->
<para>
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.
</para>
<para>
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:
</para>
<orderedlist>
<listitem><para>
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.
</para></listitem>
<listitem><para>
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().
</para></listitem>
<listitem><para>
Then the event is passed on a stack so you can query the currently handled
event with gtk_get_current_event().
</para></listitem>
<listitem><para>
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:
<itemizedlist>
<listitem><para>
Deletion and destruction events are still sent to the event widget for
obvious reasons.
</para></listitem>
<listitem><para>
Events which directly relate to the visual representation of the event
widget.
</para></listitem>
<listitem><para>
Leave events are delivered to the event widget if there was an enter
event delivered to it before without the paired leave event.
</para></listitem>
<listitem><para>
Drag events are not redirected because it is unclear what the semantics
of that would be.
</para></listitem>
</itemizedlist>
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.
</para></listitem>
<listitem><para>
After finishing the delivery the event is popped from the event stack.
</para></listitem>
</orderedlist>
@event: An event to process (normally) passed by GDK.
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<!-- ##### USER_FUNCTION GtkModuleInitFunc ##### -->
<para>
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.
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</para>
@argc: Pointer to the number of arguments remaining after gtk_init().
@argv: Points to the argument vector.
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<!-- ##### FUNCTION gtk_true ##### -->
<para>
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...
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</para>
<example>
<title>A persistent window</title>
<programlisting>
##include &lt;gtk/gtk.h&gt;
int
main (int argc, char **argv)
{
GtkWidget *win, *but;
gtk_init( &amp;argc, &amp;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;
}
</programlisting>
</example>
@Returns: %TRUE
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<!-- ##### FUNCTION gtk_false ##### -->
<para>
Analogical to gtk_true() this function does nothing
but always returns %FALSE.
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</para>
@Returns: %FALSE
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<!-- ##### FUNCTION gtk_grab_add ##### -->
<para>
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.
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</para>
@widget: The widget that grabs keyboard and pointer events.
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<!-- ##### FUNCTION gtk_grab_get_current ##### -->
<para>
Queries the current grab.
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</para>
@Returns: The widget which currently has the grab or %NULL if no grab is active.
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<!-- ##### FUNCTION gtk_grab_remove ##### -->
<para>
Removes the grab from the given widget. You have to pair calls to gtk_grab_add()
and gtk_grab_remove().
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</para>
@widget: The widget which gives up the grab.
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<!-- ##### FUNCTION gtk_init_add ##### -->
<para>
Registers a function to be called when the mainloop is started.
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</para>
@function: Function to invoke when gtk_main() is called next.
@data: Data to pass to that function.
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<!-- ##### FUNCTION gtk_quit_add_destroy ##### -->
<para>
Trigger destruction of @object in case the mainloop at level @main_level
is quit.
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</para>
@main_level: Level of the mainloop which shall trigger the destruction.
@object: Object to be destroyed.
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<!-- ##### FUNCTION gtk_quit_add ##### -->
<para>
Registers a function to be called when an instance of the mainloop is left.
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</para>
@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.
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<!-- ##### FUNCTION gtk_quit_add_full ##### -->
<para>
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.
</para>
<para>
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.
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</para>
@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.
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<!-- ##### FUNCTION gtk_quit_remove ##### -->
<para>
Removes a quit handler by it's identifier.
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</para>
@quit_handler_id: Identifier for the handler returned when installing it.
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<!-- ##### FUNCTION gtk_quit_remove_by_data ##### -->
<para>
Removes a quit handler identified by it's @data field.
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</para>
@data: The pointer passed as @data to gtk_quit_add() or gtk_quit_add_full().
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<!-- ##### FUNCTION gtk_timeout_add_full ##### -->
<para>
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.
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</para>
@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.
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<!-- ##### FUNCTION gtk_timeout_add ##### -->
<para>
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.
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</para>
@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.
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<!-- ##### FUNCTION gtk_timeout_remove ##### -->
<para>
Removes the given timeout destroying all information about it.
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</para>
@timeout_handler_id: The identifier returned when installing the timeout.
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<!-- ##### FUNCTION gtk_idle_add ##### -->
<para>
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.
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</para>
@function: The function to call.
@data: The information to pass to the function.
@Returns: a unique handle for this registration.
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<!-- ##### FUNCTION gtk_idle_add_priority ##### -->
<para>
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.
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</para>
@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.
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<!-- ##### FUNCTION gtk_idle_add_full ##### -->
<para>
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.
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</para>
@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.
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<!-- ##### FUNCTION gtk_idle_remove ##### -->
<para>
Removes the idle function with the given id.
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</para>
@idle_handler_id: Identifies the idle function to remove.
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<!-- ##### FUNCTION gtk_idle_remove_by_data ##### -->
<para>
Removes the idle function identified by the user data.
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</para>
@data: remove the idle function which was registered with this user data.
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<!-- ##### FUNCTION gtk_input_add_full ##### -->
<para>
Registers a function to be called when a condition becomes true
on a file descriptor.
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</para>
@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().
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<!-- ##### FUNCTION gtk_input_remove ##### -->
<para>
Removes the function with the given id.
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</para>
@input_handler_id: Identifies the function to remove.
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<!-- ##### MACRO GTK_PRIORITY_REDRAW ##### -->
<para>
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).
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</para>
<note><para>
This macro is deprecated. You should use %GDK_PRIORITY_REDRAW instead.
</para></note>
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<!-- ##### MACRO GTK_PRIORITY_RESIZE ##### -->
<para>
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.
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</para>
<!-- ##### MACRO GTK_PRIORITY_HIGH ##### -->
<para>
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.
<note><para>
This macro is deprecated. You should use %G_PRIORITY_HIGH instead.
</para></note>
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</para>
<!-- ##### MACRO GTK_PRIORITY_INTERNAL ##### -->
<para>
This priority is for GTK+ internal stuff. Don't use it in your applications.
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</para>
<!-- ##### MACRO GTK_PRIORITY_DEFAULT ##### -->
<para>
Default priority for idle functions.
<note><para>
This macro is deprecated. You should use %G_PRIORITY_DEFAULT_IDLE instead.
</para></note>
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</para>
<!-- ##### MACRO GTK_PRIORITY_LOW ##### -->
<para>
Priority for very unimportant background tasks.
<note><para>
This macro is deprecated. You should use %G_PRIORITY_LOW instead.
</para></note>
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</para>
<!-- ##### FUNCTION gtk_key_snooper_install ##### -->
<para>
Installs a key snooper function, which will get called on all key events
before delivering them normally.
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</para>
@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().
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<!-- ##### USER_FUNCTION GtkKeySnoopFunc ##### -->
<para>
Key snooper functions are called before normal event delivery.
They can be used to implement custom key event handling.
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</para>
@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.
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<!-- ##### FUNCTION gtk_key_snooper_remove ##### -->
<para>
Removes the key snooper function with the given id.
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</para>
@snooper_handler_id: Identifies the key snooper to remove.
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<!-- ##### FUNCTION gtk_get_current_event ##### -->
<para>
</para>
@Returns:
<!-- ##### FUNCTION gtk_get_current_event_time ##### -->
<para>
</para>
@Returns:
<!-- ##### FUNCTION gtk_get_current_event_state ##### -->
<para>
</para>
@state:
@Returns:
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<!-- ##### FUNCTION gtk_get_event_widget ##### -->
<para>
</para>
@event:
@Returns:
<!-- ##### FUNCTION gtk_propagate_event ##### -->
<para>
</para>
@widget:
@event: