GTK+ Reference Manual
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# General

## Name

General -- Mainloop and event handling

## Synopsis

    #include <gtk/gtk.h>

    gchar*      gtk_set_locale                  (void);
    void        gtk_init                        (int *argc,
                                                 char ***argv);
    gboolean    gtk_init_check                  (int *argc,
                                                 char ***argv);
    void        gtk_exit                        (gint error_code);
    gint        gtk_events_pending              (void);
    void        gtk_main                        (void);
    guint       gtk_main_level                  (void);
    void        gtk_main_quit                   (void);
    gint        gtk_main_iteration              (void);
    gint        gtk_main_iteration_do           (gboolean blocking);
    void        gtk_main_do_event               (GdkEvent *event);
    void        (*GtkModuleInitFunc)            (gint *argc,
                                                 gchar ***argv);

    gint        gtk_true                        (void);
    gint        gtk_false                       (void);

    void        gtk_grab_add                    (GtkWidget *widget);
    GtkWidget*  gtk_grab_get_current            (void);
    void        gtk_grab_remove                 (GtkWidget *widget);

    void        gtk_init_add                    (GtkFunction function,
                                                 gpointer data);
    void        gtk_quit_add_destroy            (guint main_level,
                                                 GtkObject *object);
    guint       gtk_quit_add                    (guint main_level,
                                                 GtkFunction function,
                                                 gpointer data);
    guint       gtk_quit_add_full               (guint main_level,
                                                 GtkFunction function,
                                                 GtkCallbackMarshal marshal,
                                                 gpointer data,
                                                 GtkDestroyNotify destroy);
    void        gtk_quit_remove                 (guint quit_handler_id);
    void        gtk_quit_remove_by_data         (gpointer data);

    guint       gtk_timeout_add_full            (guint32 interval,
                                                 GtkFunction function,
                                                 GtkCallbackMarshal marshal,
                                                 gpointer data,
                                                 GtkDestroyNotify destroy);
    guint       gtk_timeout_add                 (guint32 interval,
                                                 GtkFunction function,
                                                 gpointer data);
    void        gtk_timeout_remove              (guint timeout_handler_id);

    guint       gtk_idle_add                    (GtkFunction function,
                                                 gpointer data);
    guint       gtk_idle_add_priority           (gint priority,
                                                 GtkFunction function,
                                                 gpointer data);
    guint       gtk_idle_add_full               (gint priority,
                                                 GtkFunction function,
                                                 GtkCallbackMarshal marshal,
                                                 gpointer data,
                                                 GtkDestroyNotify destroy);
    void        gtk_idle_remove                 (guint idle_handler_id);
    void        gtk_idle_remove_by_data         (gpointer data);

    guint       gtk_input_add_full              (gint source,
                                                 GdkInputCondition condition,
                                                 GdkInputFunction function,
                                                 GtkCallbackMarshal marshal,
                                                 gpointer data,
                                                 GtkDestroyNotify destroy);
    void        gtk_input_remove                (guint input_handler_id);

    #define     GTK_PRIORITY_REDRAW
    #define     GTK_PRIORITY_RESIZE
    #define     GTK_PRIORITY_HIGH
    #define     GTK_PRIORITY_INTERNAL
    #define     GTK_PRIORITY_DEFAULT
    #define     GTK_PRIORITY_LOW

    guint       gtk_key_snooper_install         (GtkKeySnoopFunc snooper,
                                                 gpointer func_data);
    gint        (*GtkKeySnoopFunc)              (GtkWidget *grab_widget,
                                                 GdkEventKey *event,
                                                 gpointer func_data);
    void        gtk_key_snooper_remove          (guint snooper_handler_id);

    GdkEvent*   gtk_get_current_event           (void);
    GtkWidget*  gtk_get_event_widget            (GdkEvent *event);
    void        gtk_propagate_event             (GtkWidget *widget,
                                                 GdkEvent *event);

## Description

GTK uses an event oriented programming model. While conventional C programs have control over the program flow all the time this does not apply to applications written using GTK. Instead you set up some objects and register some functions ("callbacks") to be called whenever some event occurs and give control to the GTK mainloop (e.g. by calling gtk_main).

Example 1. Typical `main` 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_showall (mainwin);

      /* Let the user interact with our application */
      gtk_main();

      /* The user lost interest */
      gtk_exit (0);
    }

## Details

### gtk_set_locale ()

    gchar*      gtk_set_locale                  (void);

Sets the current locale according to the program environment. This is the same as calling the libc function setlocale(LC_ALL, "") but also takes care of the locale specific setup of the windowing system used by GDK.

You should call this function before `gtk_init` to support internationalization of your GTK+ applications.

Returns : | A string corresponding to the locale set.

### 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. `argc` and `argv` are adjusted accordingly so your own code will never see those standard arguments.

> Note: 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.

`argc` : | Address of the `argc` parameter of your `main` function. Changed if any arguments were handled.
`argv` : | Address of the `argv` parameter of `main`. Any parameters understood by `gtk_init` are stripped before return.

### 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 GUI 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.

`argc` : | A reference to the `argc` of the `main` function.
`argv` : | A reference to the `argv` of the `main` function.
Returns : | `TRUE` if the GUI has been successful initialized, `FALSE` otherwise.

### gtk_exit ()

    void        gtk_exit                        (gint error_code);

Terminate the program and return 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.

### gtk_events_pending ()

    gint        gtk_events_pending              (void);

Check if any events are pending. This can be used to update the GUI and invoke timeouts etc. while doing some time intensive computation.

Example 2. 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.

### 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 innerst invocation of the main loop return.

### gtk_main_level ()

    guint       gtk_main_level                  (void);

Ask 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.

### gtk_main_quit ()

    void        gtk_main_quit                   (void);

Makes the innermost invocation of the main loop return when it regains control.

### gtk_main_iteration ()

    gint        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 ()

    gint        gtk_main_iteration_do           (gboolean blocking);

Run a single iteration of the mainloop. If no events are available either return or block dependend 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.

### gtk_main_do_event ()

    void        gtk_main_do_event               (GdkEvent *event);

Process 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. In that case it is passed to gtk_selection_incr_event.

3. Then the event is passed on 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 keypresses 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.

`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 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.

### gtk_true ()

    gint        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...

Example 3. 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);
      gtk_signal_connect (GTK_OBJECT(win), "delete-event",
                          (GtkSignalFunc) gtk_true, NULL);
      gtk_signal_connect (GTK_OBJECT(win), "destroy",
    		      (GtkSignalFunc) gtk_main_quit, NULL);

      but = gtk_button_new_with_label ("Close yourself. I mean it!");
      gtk_signal_connect_object (
    		  GTK_OBJECT (but), "clicked",
    		  (GtkSignalFunc) gtk_object_destroy, (gpointer) win );
      gtk_container_add (GTK_CONTAINER (win), but);

      gtk_widget_show_all (win);
      gtk_main();
      return 0;
    }

Returns : | `TRUE`

### gtk_false ()

    gint        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`.

`widget` : | The widget that grabs keyboard and pointer events.

### gtk_grab_get_current ()

    GtkWidget*  gtk_grab_get_current            (void);

Queries the current grab.

Returns : | The widget which currently has the grab or `NULL` if no grab is active.

### gtk_grab_remove ()

    void        gtk_grab_remove                 (GtkWidget *widget);

Remove 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.

### gtk_init_add ()

    void        gtk_init_add                    (GtkFunction function,
                                                 gpointer data);

Register 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.

### gtk_quit_add_destroy ()

    void        gtk_quit_add_destroy            (guint main_level,
                                                 GtkObject *object);

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.

### gtk_quit_add ()

    guint       gtk_quit_add                    (guint main_level,
                                                 GtkFunction function,
                                                 gpointer data);

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`.

### gtk_quit_add_full ()

    guint       gtk_quit_add_full               (guint main_level,
                                                 GtkFunction function,
                                                 GtkCallbackMarshal marshal,
                                                 gpointer data,
                                                 GtkDestroyNotify destroy);

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`.

### gtk_quit_remove ()

    void        gtk_quit_remove                 (guint quit_handler_id);

Remove a quit handler by it's identifier.

`quit_handler_id` : | Identifier for the handler returned when installing it.

### gtk_quit_remove_by_data ()

    void        gtk_quit_remove_by_data         (gpointer data);

Remove a quit handler identified by it's `data` field.

`data` : | The pointer passed as `data` to gtk_quit_add() or gtk_quit_add_full().

### gtk_timeout_add_full ()

    guint       gtk_timeout_add_full            (guint32 interval,
                                                 GtkFunction function,
                                                 GtkCallbackMarshal marshal,
                                                 gpointer data,
                                                 GtkDestroyNotify destroy);

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.

### gtk_timeout_add ()

    guint       gtk_timeout_add                 (guint32 interval,
                                                 GtkFunction function,
                                                 gpointer data);

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.

### gtk_timeout_remove ()

    void        gtk_timeout_remove              (guint timeout_handler_id);

Removes the given timeout destroying all information about it.

`timeout_handler_id` : | The identifier returned when installing the timeout.

### gtk_idle_add ()

    guint       gtk_idle_add                    (GtkFunction function,
                                                 gpointer data);

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.

### gtk_idle_add_priority ()

    guint       gtk_idle_add_priority           (gint priority,
                                                 GtkFunction function,
                                                 gpointer data);

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.

### gtk_idle_add_full ()

    guint       gtk_idle_add_full               (gint priority,
                                                 GtkFunction function,
                                                 GtkCallbackMarshal marshal,
                                                 gpointer data,
                                                 GtkDestroyNotify destroy);

`priority` : |
`function` : |
`marshal` : |
`data` : |
`destroy` : |
Returns : |

### gtk_idle_remove ()

    void        gtk_idle_remove                 (guint idle_handler_id);

Removes the idle function with the given id.

`idle_handler_id` : | Identifies the idle function to remove.

### gtk_idle_remove_by_data ()

    void        gtk_idle_remove_by_data         (gpointer data);

Removes the idle function identified by the user data.

`data` : | remove the idle function which was registered with this user data.

### gtk_input_add_full ()

    guint       gtk_input_add_full              (gint source,
                                                 GdkInputCondition condition,
                                                 GdkInputFunction function,
                                                 GtkCallbackMarshal marshal,
                                                 gpointer data,
                                                 GtkDestroyNotify destroy);

`source` : |
`condition` : |
`function` : |
`marshal` : |
`data` : |
`destroy` : |
Returns : |

### gtk_input_remove ()

    void        gtk_input_remove                (guint input_handler_id);

`input_handler_id` : |

### GTK_PRIORITY_REDRAW

    #define GTK_PRIORITY_REDRAW     (G_PRIORITY_HIGH_IDLE + 20)

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).

### GTK_PRIORITY_RESIZE

    #define GTK_PRIORITY_RESIZE     (G_PRIORITY_HIGH_IDLE + 10)

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.

### GTK_PRIORITY_HIGH

    #define GTK_PRIORITY_HIGH       G_PRIORITY_HIGH

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: This macro is deprecated. You should use G_PRIORITY_HIGH instead.

### GTK_PRIORITY_INTERNAL

    #define GTK_PRIORITY_INTERNAL   GTK_PRIORITY_REDRAW

This priority is for GTK+ internal stuff. Don't use it in your applications.

### GTK_PRIORITY_DEFAULT

    #define GTK_PRIORITY_DEFAULT	G_PRIORITY_DEFAULT_IDLE

Default priority for idle functions.

> Note: This macro is deprecated. You should use G_PRIORITY_DEFAULT_IDLE instead.

### GTK_PRIORITY_LOW

    #define GTK_PRIORITY_LOW	G_PRIORITY_LOW

Priority for very unimportant background tasks.

> Note: This macro is deprecated. You should use G_PRIORITY_LOW instead.

### gtk_key_snooper_install ()

    guint       gtk_key_snooper_install         (GtkKeySnoopFunc snooper,
                                                 gpointer func_data);

`snooper` : |
`func_data` : |
Returns : |

### GtkKeySnoopFunc ()

    gint        (*GtkKeySnoopFunc)              (GtkWidget *grab_widget,
                                                 GdkEventKey *event,
                                                 gpointer func_data);

`grab_widget` : |
`event` : |
`func_data` : |
Returns : |

### gtk_key_snooper_remove ()

    void        gtk_key_snooper_remove          (guint snooper_handler_id);

`snooper_handler_id` : |

### gtk_get_current_event ()

    GdkEvent*   gtk_get_current_event           (void);

Returns : |

### gtk_get_event_widget ()

    GtkWidget*  gtk_get_event_widget            (GdkEvent *event);

`event` : |
Returns : |

### gtk_propagate_event ()

    void        gtk_propagate_event             (GtkWidget *widget,
                                                 GdkEvent *event);

`widget` : |
`event` : |

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