Main loop and Events: GTK+ 3 Reference Manual

## Main loop and Events Main loop and Events — Library initialization, main event loop, and events |

## Functions

void | gtk_disable_setlocale ()
PangoLanguage * | gtk_get_default_language ()
GtkTextDirection | gtk_get_locale_direction ()
gboolean | gtk_parse_args ()
void | gtk_init ()
gboolean | gtk_init_check ()
gboolean | gtk_init_with_args ()
GOptionGroup * | gtk_get_option_group ()
gboolean | gtk_events_pending ()
void | gtk_main ()
guint | gtk_main_level ()
void | gtk_main_quit ()
gboolean | gtk_main_iteration ()
gboolean | gtk_main_iteration_do ()
void | gtk_main_do_event ()
void | (*GtkModuleInitFunc) ()
void | (*GtkModuleDisplayInitFunc) ()
gboolean | gtk_true ()
gboolean | gtk_false ()
void | gtk_grab_add ()
GtkWidget * | gtk_grab_get_current ()
void | gtk_grab_remove ()
void | gtk_device_grab_add ()
void | gtk_device_grab_remove ()
guint | gtk_key_snooper_install ()
gint | (*GtkKeySnoopFunc) ()
void | gtk_key_snooper_remove ()
GdkEvent * | gtk_get_current_event ()
guint32 | gtk_get_current_event_time ()
gboolean | gtk_get_current_event_state ()
GdkDevice * | gtk_get_current_event_device ()
GtkWidget * | gtk_get_event_widget ()
void | gtk_propagate_event ()

## Types and Values

#define | GTK_PRIORITY_RESIZE

## Includes

    #include <gtk/gtk.h>

## 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

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    int
    main (int argc, char **argv)
    {
     GtkWidget *mainwin;
      // Initialize i18n support with bindtextdomain(), etc.

      // ...

      // 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.

## 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:

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    setlocale (LC_ALL, new_locale);
    direction = gtk_get_locale_direction ();
    gtk_widget_set_default_direction (direction);

#### Returns

the GtkTextDirection of the current locale

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.

#### Parameters

argc | a pointer to the number of command line arguments. | [inout]
argv | a pointer to the array of command line arguments. | [array length=argc][inout]

#### 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.

#### Parameters

argc | Address of the `argc` parameter of your `main()` function (or 0 if `argv` is `NULL`). This will be changed if any arguments were handled. | [inout]
argv | Address of the `argv` parameter of `main()`, or `NULL`. Any options understood by GTK+ are stripped before return. | [array length=argc][inout][allow-none]

### 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.

#### Parameters

argc | Address of the `argc` parameter of your `main()` function (or 0 if `argv` is `NULL`). This will be changed if any arguments were handled. | [inout]
argv | Address of the `argv` parameter of `main()`, or `NULL`. Any options understood by GTK+ are stripped before return. | [array length=argc][inout][allow-none]

#### 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.

#### Parameters

argc | Address of the `argc` parameter of your `main()` function (or 0 if `argv` is `NULL`). This will be changed if any arguments were handled. | [inout]
argv | Address of the `argv` parameter of `main()`, or `NULL`. Any options understood by GTK+ are stripped before return. | [array length=argc][inout][allow-none]
parameter_string | a string which is displayed in the first line of `--help` output, after `programname [OPTION...]`. | [allow-none]
entries | a `NULL`-terminated array of GOptionEntrys describing the options of your program. | [array zero-terminated=1]
translation_domain | a translation domain to use for translating the `--help` output for the options in `entries` and the `parameter_string` with `gettext()`, or `NULL`. | [nullable]
error | a return location for errors |

#### 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_get_option_group ()

    GOptionGroup *
    gtk_get_option_group (gboolean open_default_display);

Returns a GOptionGroup for the commandline arguments recognized by GTK+ and GDK.

You should add this group to your GOptionContext with `g_option_context_add_group()`, if you are using `g_option_context_parse()` to parse your commandline arguments.

#### Parameters

open_default_display | whether to open the default display when parsing the commandline arguments |

#### Returns

a GOptionGroup for the commandline arguments recognized by GTK+.

[transfer full]

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

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    // computation going on...

    while (gtk_events_pending ())
      gtk_main_iteration ();

    // ...computation continued

#### 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.

#### Returns

`TRUE` if `gtk_main_quit()` has been called for the innermost mainloop

### 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` .

#### Parameters

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

### 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:

1. 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.

2. 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.

3. Then the event is pushed onto a stack so you can query the currently handled event with `gtk_get_current_event()`.

4. 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.

5. After finishing the delivery the event is popped from the event stack.

#### Parameters

event | An event to process (normally passed by GDK) |

### 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.

#### Parameters

argc | GTK+ always passes `NULL` for this argument. | [allow-none]
argv | GTK+ always passes `NULL` for this argument. | [allow-none][array length=argc]

### 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.

#### Parameters

display | an open GdkDisplay |

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...

#### A persistent window

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    #include <gtk/gtk.h>

    int
    main (int argc, char **argv)
    {
      GtkWidget *win, *but;
      const char *text = "Close yourself. I mean it!";

      gtk_init (&argc, &argv);

      win = gtk_window_new (GTK_WINDOW_TOPLEVEL);
      g_signal_connect (win,
                        "delete-event",
                        G_CALLBACK (gtk_true),
                        NULL);
      g_signal_connect (win, "destroy",
                        G_CALLBACK (gtk_main_quit),
                        NULL);

      but = gtk_button_new_with_label (text);
      g_signal_connect_swapped (but, "clicked",
                                G_CALLBACK (gtk_object_destroy),
                                win);
      gtk_container_add (GTK_CONTAINER (win), but);

      gtk_widget_show_all (win);

      gtk_main ();

      return 0;
    }

#### Returns

`TRUE`

### gtk_false ()

    gboolean
    gtk_false (void);

Analogical to `gtk_true()`, this function does nothing but always returns `FALSE`.

#### 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]

#### Parameters

widget | The widget that grabs keyboard and pointer events |

### 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]

#### Parameters

widget | The widget which gives up the grab |

### 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.

#### Parameters

widget | a GtkWidget |
device | a GdkDevice to grab on. |
block_others | `TRUE` to prevent other devices to interact with `widget` . |

Since: 3.0

### gtk_device_grab_remove ()

    void
    gtk_device_grab_remove (GtkWidget *widget,
                            GdkDevice *device);

Removes a device grab from the given widget.

You have to pair calls to `gtk_device_grab_add()` and `gtk_device_grab_remove()`.

#### Parameters

widget | a GtkWidget |
device | a GdkDevice |

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]

#### Parameters

snooper | a GtkKeySnoopFunc |
func_data | data to pass to `snooper` . | [closure]

#### Returns

a unique id for this key snooper for use with `gtk_key_snooper_remove()`.

### 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.

#### Parameters

grab_widget | the widget to which the event will be delivered |
event | the key event |
func_data | data supplied to `gtk_key_snooper_install()`. | [closure]

#### 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.

#### Parameters

snooper_handler_id | Identifies the key snooper to remove |

### 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`.

#### Returns

the timestamp from the current event, or `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`.

#### Parameters

state | a location to store the state of the current event. | [out]

#### 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`.

#### Returns

a GdkDevice, or `NULL`.

[transfer none][nullable]

### 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.

#### Parameters

event | a GdkEvent |

#### 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.

#### Parameters

widget | a GtkWidget |
event | an event |

## Types and Values

### GTK_PRIORITY_RESIZE

    #define GTK_PRIORITY_RESIZE (G_PRIORITY_HIGH_IDLE + 10)

Use this priority for functionality related to size allocation.

It is used internally by GTK+ to compute the sizes of widgets. This priority is higher than `GDK_PRIORITY_REDRAW` to avoid resizing a widget which was just redrawn.

## See Also

See the GLib manual, especially GMainLoop and signal-related functions such as `g_signal_connect()`