## Using a Context Menu

The Panel Applet library uses GtkAction to define menu items appearing in the context menu of the applet.

### Guidelines for Context Menu

To help guarantee consistency in the interaction with applets, there are some guidelines that are recommended to follow:

- Do not make the context menu too long: if you have more than five or six menu items, then it might be worth investing efforts on rethinking what is important in the menu.

- For the menu item that will enable the user to configure the applet, use "Preferences" for the label, and try to avoid "Configure", "Configuration", "Settings", etc.

- Avoid putting a "Help" menu item. The user will usually explicitly add the applet, so it is expected that he knows what the applet is about. Putting a "Help" menu item in the context menu is therefore too prominent. It might make sense to add a "Help" button in the Preferences dialog, though.

- If you agree, avoid putting a "About" menu item. To the user, applets are not different applications but elements of one global application, the panel. Of course, this means that credits for working on the applet are not visible to the user.

### Setting Up the Menu

The only part of dealing with a context menu that is specific to applets is how to setup the context menu. Once it is setup, this is really just a matter of using GtkAction.

To setup the context menu of the applet, the `panel_applet_setup_menu_from_file()` function should be used, with a path to a menu XML file and a GtkActionGroup object containing all actions that are used in the menu XML file. The example below shows how to achieve this:

Example 3. Hello World applet, with a context menu

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    #include <glib/gi18n.h>
    #include <gtk/gtk.h>
    #include <panel-applet.h>

    /* This would usually be defined in config.h */
    #define GETTEXT_PACKAGE "hello-world"
    /* This would usually be defined in Makefile.am */
    #define HELLO_WORLD_UI_DIR "/usr/share/hello-world"

    static void hello_world_applet_prefs (GtkAction   *action,
                                          PanelApplet *applet);
    static void hello_world_applet_say   (GtkAction   *action,
                                          PanelApplet *applet);

    static const GtkActionEntry hello_world_menu_actions [] = {
            { "HelloWorldPrefs", GTK_STOCK_HELP, N_("_Preferences"),
              NULL, NULL,
              G_CALLBACK (hello_world_applet_prefs) },
            { "HelloWorldSay", GTK_STOCK_ABOUT, N_("_Say Hello"),
              NULL, NULL,
              G_CALLBACK (hello_world_applet_say) }
    };

    static void
    hello_world_applet_prefs (GtkAction   *action,
                              PanelApplet *applet)
    {
        GtkWidget *dialog;
        dialog = gtk_message_dialog_new (NULL, 0,
                                        GTK_MESSAGE_INFO, GTK_BUTTONS_CLOSE,
                                        "Preferences");
        g_signal_connect (dialog, "response",
                          G_CALLBACK (gtk_widget_destroy), NULL);
        gtk_widget_show (dialog);
    }

    static void
    hello_world_applet_say (GtkAction   *action,
                            PanelApplet *applet)
    {
        GtkWidget *dialog;
        dialog = gtk_message_dialog_new (NULL, 0,
                                        GTK_MESSAGE_INFO, GTK_BUTTONS_CLOSE,
                                        "Hello World!");
        g_signal_connect (dialog, "response",
                          G_CALLBACK (gtk_widget_destroy), NULL);
        gtk_widget_show (dialog);
    }

    static gboolean
    hello_world_applet_start (PanelApplet *applet)
    {
        GtkWidget *label;
        GtkActionGroup *action_group;
        gchar *ui_path;

        label = gtk_label_new ("Hello World");
        gtk_container_add (GTK_CONTAINER (applet), label);

        action_group = gtk_action_group_new ("Hello World Applet Actions");
        gtk_action_group_set_translation_domain (action_group, GETTEXT_PACKAGE);
        gtk_action_group_add_actions (action_group,
                                      hello_world_menu_actions,
                                      G_N_ELEMENTS (hello_world_menu_actions),
                                      applet);

        ui_path = g_build_filename (HELLO_WORLD_UI_DIR, "hello-world-menu.xml", NULL);
        panel_applet_setup_menu_from_file (applet, ui_path, action_group);

        g_free (ui_path);
        g_object_unref (action_group);

        gtk_widget_show_all (GTK_WIDGET (applet));

        return TRUE;
    }

    static gboolean
    hello_world_factory_callback (PanelApplet  *applet,
                                  const gchar  *iid,
                                  gpointer      data)
    {
        gboolean retval = FALSE;

        if (g_strcmp0 (iid, "HelloWorldApplet") == 0)
            retval = hello_world_applet_start (applet);

        return retval;
    }

    PANEL_APPLET_OUT_PROCESS_FACTORY ("HelloWorldFactory",
                                      PANEL_TYPE_APPLET,
                                      hello_world_factory_callback,
                                      NULL)

Here are the changes compared to the simple example with no context menu:

- We define a list of GtkActionEntry entries: `hello_world_menu_actions`. This will be used later on to build GtkAction objects, with their label and callback. We obviously implement the callbacks.

- We change `hello_world_applet_start()` to define a GtkActionGroup object, to which we add, with `gtk_action_group_add_actions()`, GtkAction objects based on the GtkActionEntry entries. Note that the the last argument to `gtk_action_group_add_actions()` will be passed as user data to the callbacks.

- We also change `hello_world_applet_start()` to add this GtkActionGroup object to the context menu of the applet, by calling `panel_applet_setup_menu_from_file()`. This function takes as argument a path to the menu XML file that will define how to display the GtkAction objects in the context menu.

### Menu XML File

The file that is used to setup menu with the `panel_applet_setup_menu_from_file()` function is a GtkUIManager UI definition file, without the top-level `<ui>` tag. It must only contain menuitem entries and separators. For example:

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    <menuitem name="Hello World Prefs" action="HelloWorldPrefs" />
    <separator/>
    <menuitem name="Hello World Say"   action="HelloWorldSay" />

Alternatively, the `panel_applet_setup_menu()` function can be used with a string containing directly the XML.