GApplication

## GApplication GApplication — Core application class |

## Synopsis

                        GApplication;
    struct              GApplicationClass;

    enum                GApplicationFlags;
    gboolean            g_application_id_is_valid           (const gchar *application_id);
    GApplication *      g_application_new                   (const gchar *application_id,
                                                             GApplicationFlags flags);

    const gchar *       g_application_get_application_id    (GApplication *application);
    void                g_application_set_application_id    (GApplication *application,
                                                             const gchar *application_id);

    guint               g_application_get_inactivity_timeout
                                                            (GApplication *application);
    void                g_application_set_inactivity_timeout
                                                            (GApplication *application,
                                                             guint inactivity_timeout);

    GApplicationFlags   g_application_get_flags             (GApplication *application);
    void                g_application_set_flags             (GApplication *application,
                                                             GApplicationFlags flags);

    GDBusConnection *   g_application_get_dbus_connection   (GApplication *application);
    const gchar *       g_application_get_dbus_object_path  (GApplication *application);

    void                g_application_set_action_group      (GApplication *application,
                                                             GActionGroup *action_group);

    gboolean            g_application_get_is_registered     (GApplication *application);
    gboolean            g_application_get_is_remote         (GApplication *application);
    gboolean            g_application_register              (GApplication *application,
                                                             GCancellable *cancellable,
                                                             GError **error);

    void                g_application_hold                  (GApplication *application);
    void                g_application_release               (GApplication *application);
    void                g_application_quit                  (GApplication *application);

    void                g_application_activate              (GApplication *application);
    void                g_application_open                  (GApplication *application,
                                                             GFile **files,
                                                             gint n_files,
                                                             const gchar *hint);

    int                 g_application_run                   (GApplication *application,
                                                             int argc,
                                                             char **argv);
    void                g_application_set_default           (GApplication *application);
    GApplication *      g_application_get_default           (void);

## Object Hierarchy

      GObject
       +----GApplication

      GFlags
       +----GApplicationFlags

## Implemented Interfaces

GApplication implements GActionGroup and GActionMap.

## Properties

      "action-group"             GActionGroup*         : Write
      "application-id"           gchar*                : Read / Write / Construct
      "flags"                    GApplicationFlags     : Read / Write
      "inactivity-timeout"       guint                 : Read / Write
      "is-registered"            gboolean              : Read
      "is-remote"                gboolean              : Read

## Signals

      "activate"                                       : Run Last
      "command-line"                                   : Run Last
      "open"                                           : Run Last
      "shutdown"                                       : Run Last
      "startup"                                        : Run First

## Description

A GApplication is the foundation of an application. It wraps some low-level platform-specific services and is intended to act as the foundation for higher-level application classes such as GtkApplication or MxApplication. In general, you should not use this class outside of a higher level framework.

GApplication provides convenient life cycle management by maintaining a use count for the primary application instance. The use count can be changed using `g_application_hold()` and `g_application_release()`. If it drops to zero, the application exits. Higher-level classes such as GtkApplication employ the use count to ensure that the application stays alive as long as it has any opened windows.

Another feature that GApplication (optionally) provides is process uniqueness. Applications can make use of this functionality by providing a unique application ID. If given, only one application with this ID can be running at a time per session. The session concept is platform-dependent, but corresponds roughly to a graphical desktop login. When your application is launched again, its arguments are passed through platform communication to the already running program. The already running instance of the program is called the primary instance; for non-unique applications this is the always the current instance. On Linux, the D-Bus session bus is used for communication.

The use of GApplication differs from some other commonly-used uniqueness libraries (such as libunique) in important ways. The application is not expected to manually register itself and check if it is the primary instance. Instead, the ``main()`` function of a GApplication should do very little more than instantiating the application instance, possibly connecting signal handlers, then calling `g_application_run()`. All checks for uniqueness are done internally. If the application is the primary instance then the startup signal is emitted and the mainloop runs. If the application is not the primary instance then a signal is sent to the primary instance and `g_application_run()` promptly returns. See the code examples below.

If used, the expected form of an application identifier is very close to that of of a DBus bus name. Examples include: "com.example.MyApp", "org.example.internal-apps.Calculator". For details on valid application identifiers, see `g_application_id_is_valid()`.

On Linux, the application identifier is claimed as a well-known bus name on the user's session bus. This means that the uniqueness of your application is scoped to the current session. It also means that your application may provide additional services (through registration of other object paths) at that bus name. The registration of these object paths should be done with the shared GDBus session bus. Note that due to the internal architecture of GDBus, method calls can be dispatched at any time (even if a main loop is not running). For this reason, you must ensure that any object paths that you wish to register are registered before GApplication attempts to acquire the bus name of your application (which happens in `g_application_register()`). Unfortunately, this means that you cannot use `g_application_get_is_remote()` to decide if you want to register object paths.

GApplication also implements the GActionGroup and GActionMap interfaces and lets you easily export actions by adding them with `g_action_map_add_action()`. When invoking an action by calling `g_action_group_activate_action()` on the application, it is always invoked in the primary instance. The actions are also exported on the session bus, and GIO provides the GDBusActionGroup wrapper to conveniently access them remotely. GIO provides a GDBusMenuModel wrapper for remote access to exported GMenuModels.

There is a number of different entry points into a GApplication:

- via 'Activate' (i.e. just starting the application)
- via 'Open' (i.e. opening some files)
- by handling a command-line
- via activating an action

The "startup" signal lets you handle the application initialization for all of these in a single place.

Regardless of which of these entry points is used to start the application, GApplication passes some platform data from the launching instance to the primary instance, in the form of a GVariant dictionary mapping strings to variants. To use platform data, override the `before_emit` or `after_emit` virtual functions in your GApplication subclass. When dealing with GApplicationCommandLine objects, the platform data is directly available via `g_application_command_line_get_cwd()`, `g_application_command_line_get_environ()` and `g_application_command_line_get_platform_data()`.

As the name indicates, the platform data may vary depending on the operating system, but it always includes the current directory (key "cwd"), and optionally the environment (ie the set of environment variables and their values) of the calling process (key "environ"). The environment is only added to the platform data if the `G_APPLICATION_SEND_ENVIRONMENT` flag is set. GApplication subclasses can add their own platform data by overriding the `add_platform_data` virtual function. For instance, GtkApplication adds startup notification data in this way.

To parse commandline arguments you may handle the "command-line" signal or override the `local_command_line()` vfunc, to parse them in either the primary instance or the local instance, respectively.

Example 14. Opening files with a GApplication

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    #include <gio/gio.h>
    #include <stdlib.h>
    #include <string.h>

    static void
    activate (GApplication *application)
    {
      g_print ("activated\n");

      /* Note: when doing a longer-lasting action here that returns
       * to the mainloop, you should use g_application_hold() and
       * g_application_release() to keep the application alive until
       * the action is completed.
       */
    }

    static void
    open (GApplication  *application,
          GFile        **files,
          gint           n_files,
          const gchar   *hint)
    {
      gint i;

      for (i = 0; i < n_files; i++)
        {
          gchar *uri = g_file_get_uri (files[i]);
          g_print ("open %s\n", uri);
          g_free (uri);
        }

      /* Note: when doing a longer-lasting action here that returns
       * to the mainloop, you should use g_application_hold() and
       * g_application_release() to keep the application alive until
       * the action is completed.
       */
    }

    int
    main (int argc, char **argv)
    {
      GApplication *app;
      int status;

      app = g_application_new ("org.gtk.TestApplication",
                               G_APPLICATION_HANDLES_OPEN);
      g_signal_connect (app, "activate", G_CALLBACK (activate), NULL);
      g_signal_connect (app, "open", G_CALLBACK (open), NULL);
      g_application_set_inactivity_timeout (app, 10000);

      status = g_application_run (app, argc, argv);

      g_object_unref (app);

      return status;
    }

Example 15. A GApplication with actions

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    #include <gio/gio.h>
    #include <stdlib.h>
    #include <string.h>

    static void
    activate (GApplication *application)
    {
      g_application_hold (application);
      g_print ("activated\n");
      g_application_release (application);
    }

    static void
    activate_action (GAction  *action,
                     GVariant *parameter,
                     gpointer  data)
    {
      GApplication *application = G_APPLICATION (data);

      g_application_hold (application);
      g_print ("action %s activated\n", g_action_get_name (action));
      g_application_release (application);
    }

    static void
    activate_toggle_action (GSimpleAction *action,
                            GVariant      *parameter,
                            gpointer       data)
    {
      GApplication *application = G_APPLICATION (data);
      GVariant *state;
      gboolean b;

      g_print ("action %s activated\n", g_action_get_name (G_ACTION (action)));

      g_application_hold (application);
      state = g_action_get_state (G_ACTION (action));
      b = g_variant_get_boolean (state);
      g_variant_unref (state);
      g_simple_action_set_state (action, g_variant_new_boolean (!b));
      g_print ("state change %d -> %d\n", b, !b);
      g_application_release (application);
    }

    static void
    add_actions (GApplication *app)
    {
      GSimpleAction *action;

      action = g_simple_action_new ("simple-action", NULL);
      g_signal_connect (action, "activate", G_CALLBACK (activate_action), app);
      g_action_map_add_action (G_ACTION_MAP (app), G_ACTION (action));
      g_object_unref (action);

      action = g_simple_action_new_stateful ("toggle-action", NULL,
                                             g_variant_new_boolean (FALSE));
      g_signal_connect (action, "activate", G_CALLBACK (activate_toggle_action), app);
      g_action_map_add_action (G_ACTION_MAP (app), G_ACTION (action));
      g_object_unref (action);
    }

    static void
    describe_and_activate_action (GActionGroup *group,
                                  const gchar  *name)
    {
      const GVariantType *param_type;
      GVariant *state;
      gboolean enabled;
      gchar *tmp;

      param_type = g_action_group_get_action_parameter_type (group, name);
      state = g_action_group_get_action_state (group, name);
      enabled = g_action_group_get_action_enabled (group, name);

      g_print ("action name:      %s\n", name);
      tmp = param_type ? g_variant_type_dup_string (param_type) : NULL;
      g_print ("parameter type:   %s\n", tmp ? tmp : "<none>");
      g_free (tmp);
      g_print ("state type:       %s\n",
               state ? g_variant_get_type_string (state) : "<none>");
      tmp = state ? g_variant_print (state, FALSE) : NULL;
      g_print ("state:            %s\n", tmp ? tmp : "<none>");
      g_free (tmp);
      g_print ("enabled:          %s\n", enabled ? "true" : "false");

      if (state != NULL)
        g_variant_unref (state);

      g_action_group_activate_action (group, name, NULL);
    }

    int
    main (int argc, char **argv)
    {
      GApplication *app;
      int status;

      app = g_application_new ("org.gtk.TestApplication", 0);
      g_signal_connect (app, "activate", G_CALLBACK (activate), NULL);
      g_application_set_inactivity_timeout (app, 10000);

      add_actions (app);

      if (argc > 1 && strcmp (argv[1], "--simple-action") == 0)
        {
          g_application_register (app, NULL, NULL);
          describe_and_activate_action (G_ACTION_GROUP (app), "simple-action");
          exit (0);
        }
      else if (argc > 1 && strcmp (argv[1], "--toggle-action") == 0)
        {
          g_application_register (app, NULL, NULL);
          describe_and_activate_action (G_ACTION_GROUP (app), "toggle-action");
          exit (0);
        }

      status = g_application_run (app, argc, argv);

      g_object_unref (app);

      return status;
    }

Example 16. A GApplication with menus

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Example 17. Using extra D-Bus hooks with a GApplication

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    #include <gio/gio.h>
    #include <stdlib.h>
    #include <string.h>

    static void
    activate (GApplication *application)
    {
      g_print ("activated\n");

      /* Note: when doing a longer-lasting action here that returns
       * to the mainloop, you should use g_application_hold() and
       * g_application_release() to keep the application alive until
       * the action is completed.
       */
    }

    typedef GApplication TestApplication;
    typedef GApplicationClass TestApplicationClass;

    static GType test_application_get_type (void);
    G_DEFINE_TYPE (TestApplication, test_application, G_TYPE_APPLICATION)

    static gboolean
    test_application_dbus_register (GApplication    *application,
                                    GDBusConnection *connection,
                                    const gchar     *object_path,
                                    GError         **error)
    {
      /* We must chain up to the parent class */
      if (!G_APPLICATION_CLASS (test_application_parent_class)->dbus_register (application,
                                                                               connection,
                                                                               object_path,
                                                                               error))
        return FALSE;

      /* Now we can do our own stuff here. For example, we could export some D-Bus objects */
      return TRUE;
    }

    static void
    test_application_dbus_unregister (GApplication    *application,
                                      GDBusConnection *connection,
                                      const gchar     *object_path)
    {
      /* Do our own stuff here, e.g. unexport any D-Bus objects we exported in the dbus_register
       * hook above. Be sure to check that we actually did export them, since the hook
       * above might have returned early due to the parent class' hook returning FALSE!
       */

      /* Lastly, we must chain up to the parent class */
      G_APPLICATION_CLASS (test_application_parent_class)->dbus_unregister (application,
                                                                            connection,
                                                                            object_path);
    }

    static void
    test_application_init (TestApplication *app)
    {
    }

    static void
    test_application_class_init (TestApplicationClass *class)
    {
      GApplicationClass *g_application_class = G_APPLICATION_CLASS (class);

      g_application_class->dbus_register = test_application_dbus_register;
      g_application_class->dbus_unregister = test_application_dbus_unregister;
    }

    static GApplication *
    test_application_new (const gchar       *application_id,
                          GApplicationFlags  flags)
    {
      g_return_val_if_fail (g_application_id_is_valid (application_id), NULL);

      g_type_init ();

      return g_object_new (test_application_get_type (),
                           "application-id", application_id,
                           "flags", flags,
                           NULL);
    }

    int
    main (int argc, char **argv)
    {
      GApplication *app;
      int status;

      app = test_application_new ("org.gtk.TestApplication", 0);
      g_signal_connect (app, "activate", G_CALLBACK (activate), NULL);
      g_application_set_inactivity_timeout (app, 10000);

      status = g_application_run (app, argc, argv);

      g_object_unref (app);

      return status;
    }

## Details

### GApplication

    typedef struct _GApplication GApplication;

Since 2.28

### struct GApplicationClass

    struct GApplicationClass {
      /* signals */
      void                      (* startup)             (GApplication              *application);

      void                      (* activate)            (GApplication              *application);

      void                      (* open)                (GApplication              *application,
                                                         GFile                    **files,
                                                         gint                       n_files,
                                                         const gchar               *hint);

      int                       (* command_line)        (GApplication              *application,
                                                         GApplicationCommandLine   *command_line);

      /* vfuncs */
      gboolean                  (* local_command_line)  (GApplication              *application,
                                                         gchar                   ***arguments,
                                                         int                       *exit_status);

      void                      (* before_emit)         (GApplication              *application,
                                                         GVariant                  *platform_data);
      void                      (* after_emit)          (GApplication              *application,
                                                         GVariant                  *platform_data);
      void                      (* add_platform_data)   (GApplication              *application,
                                                         GVariantBuilder           *builder);
      void                      (* quit_mainloop)       (GApplication              *application);
      void                      (* run_mainloop)        (GApplication              *application);
      void                      (* shutdown)            (GApplication              *application);

      gboolean                  (* dbus_register)       (GApplication              *application,
                                                         GDBusConnection           *connection,
                                                         const gchar               *object_path,
                                                         GError                   **error);
      void                      (* dbus_unregister)     (GApplication              *application,
                                                         GDBusConnection           *connection,
                                                         const gchar               *object_path);
    };

Virtual function table for GApplication.

`startup` () | invoked on the primary instance immediately after registration
`activate` () | invoked on the primary instance when an activation occurs
`open` () | invoked on the primary instance when there are files to open
`command_line` () | invoked on the primary instance when a command-line is not handled locally
`local_command_line` () | invoked (locally) when the process has been invoked via commandline execution (as opposed to, say, D-Bus activation - which is not currently supported by GApplication). The virtual function has the chance to inspect (and possibly replace) the list of command line arguments. See `g_application_run()` for more information.
`before_emit` () | invoked on the primary instance before 'activate', 'open', 'command-line' or any action invocation, gets the 'platform data' from the calling instance
`after_emit` () | invoked on the primary instance after 'activate', 'open', 'command-line' or any action invocation, gets the 'platform data' from the calling instance
`add_platform_data` () | invoked (locally) to add 'platform data' to be sent to the primary instance when activating, opening or invoking actions
`quit_mainloop` () | Used to be invoked on the primary instance when the use count of the application drops to zero (and after any inactivity timeout, if requested). Not used anymore since 2.32
`run_mainloop` () | Used to be invoked on the primary instance from `g_application_run()` if the use-count is non-zero. Since 2.32, GApplication is iterating the main context directly and is not using `run_mainloop` anymore
`shutdown` () | invoked only on the registered primary instance immediately after the main loop terminates
`dbus_register` () | invoked locally during registration, if the application is using its D-Bus backend. You can use this to export extra objects on the bus, that need to exist before the application tries to own the bus name. The function is passed the GDBusConnection to to session bus, and the object path that GApplication will use to export is D-Bus API. If this function returns `TRUE`, registration will proceed; otherwise registration will abort. Since: 2.34
`dbus_unregister` () | invoked locally during unregistration, if the application is using its D-Bus backend. Use this to undo anything done by the `dbus_register` vfunc. Since: 2.34

Since 2.28

### enum GApplicationFlags

    typedef enum {
      G_APPLICATION_FLAGS_NONE,
      G_APPLICATION_IS_SERVICE  =          (1 << 0),
      G_APPLICATION_IS_LAUNCHER =          (1 << 1),

      G_APPLICATION_HANDLES_OPEN =         (1 << 2),
      G_APPLICATION_HANDLES_COMMAND_LINE = (1 << 3),
      G_APPLICATION_SEND_ENVIRONMENT    =  (1 << 4),

      G_APPLICATION_NON_UNIQUE =           (1 << 5)
    } GApplicationFlags;

Flags used to define the behaviour of a GApplication.

`G_APPLICATION_FLAGS_NONE` | Default
`G_APPLICATION_IS_SERVICE` | Run as a service. In this mode, registration fails if the service is already running, and the application will stay around for a while when the use count falls to zero.
`G_APPLICATION_IS_LAUNCHER` | Don't try to become the primary instance.
`G_APPLICATION_HANDLES_OPEN` | This application handles opening files (in the primary instance). Note that this flag only affects the default implementation of `local_command_line()`, and has no effect if `G_APPLICATION_HANDLES_COMMAND_LINE` is given. See `g_application_run()` for details.
`G_APPLICATION_HANDLES_COMMAND_LINE` | This application handles command line arguments (in the primary instance). Note that this flag only affect the default implementation of `local_command_line()`. See `g_application_run()` for details.
`G_APPLICATION_SEND_ENVIRONMENT` | Send the environment of the launching process to the primary instance. Set this flag if your application is expected to behave differently depending on certain environment variables. For instance, an editor might be expected to use the `GIT_COMMITTER_NAME` environment variable when editing a git commit message. The environment is available to the "command-line" signal handler, via `g_application_command_line_getenv()`.
`G_APPLICATION_NON_UNIQUE` | Make no attempts to do any of the typical single-instance application negotiation, even if the application ID is given. The application neither attempts to become the owner of the application ID nor does it check if an existing owner already exists. Everything occurs in the local process. Since: 2.30.

Since 2.28

### g_application_id_is_valid ()

    gboolean            g_application_id_is_valid           (const gchar *application_id);

Checks if `application_id` is a valid application identifier.

A valid ID is required for calls to `g_application_new()` and `g_application_set_application_id()`.

For convenience, the restrictions on application identifiers are reproduced here:

- Application identifiers must contain only the ASCII characters "[A-Z][a-z][0-9]_-." and must not begin with a digit.
- Application identifiers must contain at least one '.' (period) character (and thus at least three elements).
- Application identifiers must not begin or end with a '.' (period) character.
- Application identifiers must not contain consecutive '.' (period) characters.
- Application identifiers must not exceed 255 characters.

`application_id` : | a potential application identifier
Returns : | `TRUE` if `application_id` is valid

### g_application_new ()

    GApplication *      g_application_new                   (const gchar *application_id,
                                                             GApplicationFlags flags);

Creates a new GApplication instance.

This function calls `g_type_init()` for you.

If non-`NULL`, the application id must be valid. See `g_application_id_is_valid()`.

If no application ID is given then some features of GApplication (most notably application uniqueness) will be disabled.

`application_id` : | the application id. [allow-none]
`flags` : | the application flags
Returns : | a new GApplication instance

### g_application_get_application_id ()

    const gchar *       g_application_get_application_id    (GApplication *application);

Gets the unique identifier for `application`.

`application` : | a GApplication
Returns : | the identifier for `application`, owned by `application`

Since 2.28

### g_application_set_application_id ()

    void                g_application_set_application_id    (GApplication *application,
                                                             const gchar *application_id);

Sets the unique identifier for `application`.

The application id can only be modified if `application` has not yet been registered.

If non-`NULL`, the application id must be valid. See `g_application_id_is_valid()`.

`application` : | a GApplication
`application_id` : | the identifier for `application`. [allow-none]

Since 2.28

### g_application_get_inactivity_timeout ()

    guint               g_application_get_inactivity_timeout
                                                            (GApplication *application);

Gets the current inactivity timeout for the application.

This is the amount of time (in milliseconds) after the last call to `g_application_release()` before the application stops running.

`application` : | a GApplication
Returns : | the timeout, in milliseconds

Since 2.28

### g_application_set_inactivity_timeout ()

    void                g_application_set_inactivity_timeout
                                                            (GApplication *application,
                                                             guint inactivity_timeout);

Sets the current inactivity timeout for the application.

This is the amount of time (in milliseconds) after the last call to `g_application_release()` before the application stops running.

This call has no side effects of its own. The value set here is only used for next time `g_application_release()` drops the use count to zero. Any timeouts currently in progress are not impacted.

`application` : | a GApplication
`inactivity_timeout` : | the timeout, in milliseconds

Since 2.28

### g_application_get_flags ()

    GApplicationFlags   g_application_get_flags             (GApplication *application);

Gets the flags for `application`.

See GApplicationFlags.

`application` : | a GApplication
Returns : | the flags for `application`

Since 2.28

### g_application_set_flags ()

    void                g_application_set_flags             (GApplication *application,
                                                             GApplicationFlags flags);

Sets the flags for `application`.

The flags can only be modified if `application` has not yet been registered.

See GApplicationFlags.

`application` : | a GApplication
`flags` : | the flags for `application`

Since 2.28

### g_application_get_dbus_connection ()

    GDBusConnection *   g_application_get_dbus_connection   (GApplication *application);

Gets the GDBusConnection being used by the application, or `NULL`.

If GApplication is using its D-Bus backend then this function will return the GDBusConnection being used for uniqueness and communication with the desktop environment and other instances of the application.

If GApplication is not using D-Bus then this function will return `NULL`. This includes the situation where the D-Bus backend would normally be in use but we were unable to connect to the bus.

This function must not be called before the application has been registered. See `g_application_get_is_registered()`.

`application` : | a GApplication
Returns : | a GDBusConnection, or `NULL`. [transfer none]

Since 2.34

### g_application_get_dbus_object_path ()

    const gchar *       g_application_get_dbus_object_path  (GApplication *application);

Gets the D-Bus object path being used by the application, or `NULL`.

If GApplication is using its D-Bus backend then this function will return the D-Bus object path that GApplication is using. If the application is the primary instance then there is an object published at this path. If the application is not the primary instance then the result of this function is undefined.

If GApplication is not using D-Bus then this function will return `NULL`. This includes the situation where the D-Bus backend would normally be in use but we were unable to connect to the bus.

This function must not be called before the application has been registered. See `g_application_get_is_registered()`.

`application` : | a GApplication
Returns : | the object path, or `NULL`

Since 2.34

### g_application_set_action_group ()

    void                g_application_set_action_group      (GApplication *application,
                                                             GActionGroup *action_group);

### Warning

`g_application_set_action_group` has been deprecated since version 2.32 and should not be used in newly-written code. Use the GActionMap interface instead. Never ever mix use of this API with use of GActionMap on the same `application` or things will go very badly wrong. This function is known to introduce buggy behaviour (ie: signals not emitted on changes to the action group), so you should really use GActionMap instead.

This used to be how actions were associated with a GApplication. Now there is GActionMap for that.

`application` : | a GApplication
`action_group` : | a GActionGroup, or `NULL`. [allow-none]

Since 2.28

### g_application_get_is_registered ()

    gboolean            g_application_get_is_registered     (GApplication *application);

Checks if `application` is registered.

An application is registered if `g_application_register()` has been successfully called.

`application` : | a GApplication
Returns : | `TRUE` if `application` is registered

Since 2.28

### g_application_get_is_remote ()

    gboolean            g_application_get_is_remote         (GApplication *application);

Checks if `application` is remote.

If `application` is remote then it means that another instance of application already exists (the 'primary' instance). Calls to perform actions on `application` will result in the actions being performed by the primary instance.

The value of this property cannot be accessed before `g_application_register()` has been called. See `g_application_get_is_registered()`.

`application` : | a GApplication
Returns : | `TRUE` if `application` is remote

Since 2.28

### g_application_register ()

    gboolean            g_application_register              (GApplication *application,
                                                             GCancellable *cancellable,
                                                             GError **error);

Attempts registration of the application.

This is the point at which the application discovers if it is the primary instance or merely acting as a remote for an already-existing primary instance. This is implemented by attempting to acquire the application identifier as a unique bus name on the session bus using GDBus.

If there is no application ID or if `G_APPLICATION_NON_UNIQUE` was given, then this process will always become the primary instance.

Due to the internal architecture of GDBus, method calls can be dispatched at any time (even if a main loop is not running). For this reason, you must ensure that any object paths that you wish to register are registered before calling this function.

If the application has already been registered then `TRUE` is returned with no work performed.

The "startup" signal is emitted if registration succeeds and `application` is the primary instance (including the non-unique case).

In the event of an error (such as `cancellable` being cancelled, or a failure to connect to the session bus), `FALSE` is returned and `error` is set appropriately.

Note: the return value of this function is not an indicator that this instance is or is not the primary instance of the application. See `g_application_get_is_remote()` for that.

`application` : | a GApplication
`cancellable` : | a GCancellable, or `NULL`. [allow-none]
`error` : | a pointer to a NULL GError, or `NULL`
Returns : | `TRUE` if registration succeeded

Since 2.28

### g_application_hold ()

    void                g_application_hold                  (GApplication *application);

Increases the use count of `application`.

Use this function to indicate that the application has a reason to continue to run. For example, `g_application_hold()` is called by GTK+ when a toplevel window is on the screen.

To cancel the hold, call `g_application_release()`.

`application` : | a GApplication

### g_application_release ()

    void                g_application_release               (GApplication *application);

Decrease the use count of `application`.

When the use count reaches zero, the application will stop running.

Never call this function except to cancel the effect of a previous call to `g_application_hold()`.

`application` : | a GApplication

### g_application_quit ()

    void                g_application_quit                  (GApplication *application);

Immediately quits the application.

Upon return to the mainloop, `g_application_run()` will return, calling only the 'shutdown' function before doing so.

The hold count is ignored.

The result of calling `g_application_run()` again after it returns is unspecified.

`application` : | a GApplication

Since 2.32

### g_application_activate ()

    void                g_application_activate              (GApplication *application);

Activates the application.

In essence, this results in the "activate" signal being emitted in the primary instance.

The application must be registered before calling this function.

`application` : | a GApplication

Since 2.28

### g_application_open ()

    void                g_application_open                  (GApplication *application,
                                                             GFile **files,
                                                             gint n_files,
                                                             const gchar *hint);

Opens the given files.

In essence, this results in the "open" signal being emitted in the primary instance.

`n_files` must be greater than zero.

`hint` is simply passed through to the ::open signal. It is intended to be used by applications that have multiple modes for opening files (eg: "view" vs "edit", etc). Unless you have a need for this functionality, you should use "".

The application must be registered before calling this function and it must have the `G_APPLICATION_HANDLES_OPEN` flag set.

`application` : | a GApplication
`files` : | an array of GFiles to open. [array length=n_files]
`n_files` : | the length of the `files` array
`hint` : | a hint (or ""), but never `NULL`

Since 2.28

### g_application_run ()

    int                 g_application_run                   (GApplication *application,
                                                             int argc,
                                                             char **argv);

Runs the application.

This function is intended to be run from `main()` and its return value is intended to be returned by `main()`. 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.

First, the `local_command_line()` virtual function is invoked. This function always runs on the local instance. It gets passed a pointer to a `NULL`-terminated copy of `argv` and is expected to remove the arguments that it handled (shifting up remaining arguments). See Example 19, “Split commandline handling” for an example of parsing `argv` manually. Alternatively, you may use the GOptionContext API, after setting `argc = g_strv_length (argv);`.

The last argument to `local_command_line()` is a pointer to the `status` variable which can used to set the exit status that is returned from `g_application_run()`.

If `local_command_line()` returns `TRUE`, the command line is expected to be completely handled, including possibly registering as the primary instance, calling `g_application_activate()` or `g_application_open()`, etc.

If `local_command_line()` returns `FALSE` then the application is registered and the "command-line" signal is emitted in the primary instance (which may or may not be this instance). The signal handler gets passed a GApplicationCommandLine object that (among other things) contains the remaining commandline arguments that have not been handled by `local_command_line()`.

If the application has the `G_APPLICATION_HANDLES_COMMAND_LINE` flag set then the default implementation of `local_command_line()` always returns `FALSE` immediately, resulting in the commandline always being handled in the primary instance.

Otherwise, the default implementation of `local_command_line()` tries to do a couple of things that are probably reasonable for most applications. First, `g_application_register()` is called to attempt to register the application. If that works, then the command line arguments are inspected. If no commandline arguments are given, then `g_application_activate()` is called. If commandline arguments are given and the `G_APPLICATION_HANDLES_OPEN` flag is set then they are assumed to be filenames and `g_application_open()` is called.

If you need to handle commandline arguments that are not filenames, and you don't mind commandline handling to happen in the primary instance, you should set `G_APPLICATION_HANDLES_COMMAND_LINE` and process the commandline arguments in your "command-line" signal handler, either manually or using the GOptionContext API.

If you are interested in doing more complicated local handling of the commandline then you should implement your own GApplication subclass and override `local_command_line()`. In this case, you most likely want to return `TRUE` from your `local_command_line()` implementation to suppress the default handling. See Example 19, “Split commandline handling” for an example.

If, after the above is done, the use count of the application is zero then the exit status is returned immediately. If the use count is non-zero then the default main context is iterated until the use count falls to zero, at which point 0 is returned.

If the `G_APPLICATION_IS_SERVICE` flag is set, then the exiting at use count of zero is delayed for a while (ie: the instance stays around to provide its service to others).

`application` : | a GApplication
`argc` : | the argc from `main()` (or 0 if `argv` is `NULL`)
`argv` : | the argv from `main()`, or `NULL`. [array length=argc][allow-none]
Returns : | the exit status

Since 2.28

### g_application_set_default ()

    void                g_application_set_default           (GApplication *application);

Sets or unsets the default application for the process, as returned by `g_application_get_default()`.

This function does not take its own reference on `application`. If `application` is destroyed then the default application will revert back to `NULL`.

`application` : | the application to set as default, or `NULL`. [allow-none]

Since 2.32

### g_application_get_default ()

    GApplication *      g_application_get_default           (void);

Returns the default GApplication instance for this process.

Normally there is only one GApplication per process and it becomes the default when it is created. You can exercise more control over this by using `g_application_set_default()`.

If there is no default application then `NULL` is returned.

Returns : | the default application for this process, or `NULL`. [transfer none]

Since 2.32

## Property Details

### The `"action-group"` property

      "action-group"             GActionGroup*         : Write

The group of actions that the application exports.

### The `"application-id"` property

      "application-id"           gchar*                : Read / Write / Construct

The unique identifier for the application.

Default value: NULL

### The `"flags"` property

      "flags"                    GApplicationFlags     : Read / Write

Flags specifying the behaviour of the application.

### The `"inactivity-timeout"` property

      "inactivity-timeout"       guint                 : Read / Write

Time (ms) to stay alive after becoming idle.

Default value: 0

### The `"is-registered"` property

      "is-registered"            gboolean              : Read

If g_application_register() has been called.

Default value: FALSE

### The `"is-remote"` property

      "is-remote"                gboolean              : Read

If this application instance is remote.

Default value: FALSE

## Signal Details

### The `"activate"` signal

    void                user_function                      (GApplication *application,
                                                            gpointer      user_data)        : Run Last

The ::activate signal is emitted on the primary instance when an activation occurs. See `g_application_activate()`.

`application` : | the application
`user_data` : | user data set when the signal handler was connected.

### The `"command-line"` signal

    gint                user_function                      (GApplication            *application,
                                                            GApplicationCommandLine *command_line,
                                                            gpointer                 user_data)         : Run Last

The ::command-line signal is emitted on the primary instance when a commandline is not handled locally. See `g_application_run()` and the GApplicationCommandLine documentation for more information.

`application` : | the application
`command_line` : | a GApplicationCommandLine representing the passed commandline
`user_data` : | user data set when the signal handler was connected.
Returns : | An integer that is set as the exit status for the calling process. See `g_application_command_line_set_exit_status()`.

### The `"open"` signal

    void                user_function                      (GApplication *application,
                                                            gpointer      files,
                                                            gint          n_files,
                                                            gchar        *hint,
                                                            gpointer      user_data)        : Run Last

The ::open signal is emitted on the primary instance when there are files to open. See `g_application_open()` for more information.

`application` : | the application
`files` : | an array of GFiles. [array length=n_files][element-type GFile]
`n_files` : | the length of `files`
`hint` : | a hint provided by the calling instance
`user_data` : | user data set when the signal handler was connected.

### The `"shutdown"` signal

    void                user_function                      (GApplication *application,
                                                            gpointer      user_data)        : Run Last

The ::shutdown signal is emitted only on the registered primary instance immediately after the main loop terminates.

`application` : | the application
`user_data` : | user data set when the signal handler was connected.

### The `"startup"` signal

    void                user_function                      (GApplication *application,
                                                            gpointer      user_data)        : Run First

The ::startup signal is emitted on the primary instance immediately after registration. See `g_application_register()`.

`application` : | the application
`user_data` : | user data set when the signal handler was connected.