GTK v1.2 Tutorial: Menu Widget

13. Menu Widget

There are two ways to create menus: there's the easy way, and there's the hard way. Both have their uses, but you can usually use the Itemfactory (the easy way). The "hard" way is to create all the menus using the calls directly. The easy way is to use the gtk_item_factory calls. This is much simpler, but there are advantages and disadvantages to each approach.

The Itemfactory is much easier to use, and to add new menus to, although writing a few wrapper functions to create menus using the manual method could go a long way towards usability. With the Itemfactory, it is not possible to add images or the character '/' to the menus.

13.1 Manual Menu Creation

In the true tradition of teaching, we'll show you the hard way first. :)

There are three widgets that go into making a menubar and submenus:

a menu item, which is what the user wants to select, e.g., "Save"
a menu, which acts as a container for the menu items, and
a menubar, which is a container for each of the individual menus.

This is slightly complicated by the fact that menu item widgets are used for two different things. They are both the widgets that are packed into the menu, and the widget that is packed into the menubar, which, when selected, activates the menu.

Let's look at the functions that are used to create menus and menubars. This first function is used to create a new menubar.


GtkWidget *gtk_menu_bar_new( void );

This rather self explanatory function creates a new menubar. You use gtk_container_add to pack this into a window, or the box_pack functions to pack it into a box - the same as buttons.


GtkWidget *gtk_menu_new( void );

This function returns a pointer to a new menu; it is never actually shown (with gtk_widget_show), it is just a container for the menu items. I hope this will become more clear when you look at the example below.

The next two calls are used to create menu items that are packed into the menu (and menubar).


GtkWidget *gtk_menu_item_new( void );

and


GtkWidget *gtk_menu_item_new_with_label( const char *label );

These calls are used to create the menu items that are to be displayed. Remember to differentiate between a "menu" as created with gtk_menu_new and a "menu item" as created by the gtk_menu_item_new functions. The menu item will be an actual button with an associated action, whereas a menu will be a container holding menu items.

The gtk_menu_new_with_label and gtk_menu_new functions are just as you'd expect after reading about the buttons. One creates a new menu item with a label already packed into it, and the other just creates a blank menu item.

Once you've created a menu item you have to put it into a menu. This is done using the function gtk_menu_append. In order to capture when the item is selected by the user, we need to connect to the activate signal in the usual way. So, if we wanted to create a standard File menu, with the options Open, Save, and Quit, the code would look something like:


    file_menu = gtk_menu_new ();    /* Don't need to show menus */

    /* Create the menu items */
    open_item = gtk_menu_item_new_with_label ("Open");
    save_item = gtk_menu_item_new_with_label ("Save");
    quit_item = gtk_menu_item_new_with_label ("Quit");

    /* Add them to the menu */
    gtk_menu_append (GTK_MENU (file_menu), open_item);
    gtk_menu_append (GTK_MENU (file_menu), save_item);
    gtk_menu_append (GTK_MENU (file_menu), quit_item);

    /* Attach the callback functions to the activate signal */
    gtk_signal_connect_object (GTK_OBJECT (open_items), "activate",
                               GTK_SIGNAL_FUNC (menuitem_response),
                               (gpointer) "file.open");
    gtk_signal_connect_object (GTK_OBJECT (save_items), "activate",
                               GTK_SIGNAL_FUNC (menuitem_response),
                               (gpointer) "file.save");

    /* We can attach the Quit menu item to our exit function */
    gtk_signal_connect_object (GTK_OBJECT (quit_items), "activate",
                               GTK_SIGNAL_FUNC (destroy),
                               (gpointer) "file.quit");

    /* We do need to show menu items */
    gtk_widget_show (open_item);
    gtk_widget_show (save_item);
    gtk_widget_show (quit_item);

At this point we have our menu. Now we need to create a menubar and a menu item for the File entry, to which we add our menu. The code looks like this:


    menu_bar = gtk_menu_bar_new ();
    gtk_container_add (GTK_CONTAINER (window), menu_bar);
    gtk_widget_show (menu_bar);

    file_item = gtk_menu_item_new_with_label ("File");
    gtk_widget_show (file_item);

Now we need to associate the menu with file_item. This is done with the function

void gtk_menu_item_set_submenu( GtkMenuItem *menu_item, GtkWidget *submenu );

So, our example would continue with


    gtk_menu_item_set_submenu (GTK_MENU_ITEM (file_item), file_menu);

All that is left to do is to add the menu to the menubar, which is accomplished using the function

void gtk_menu_bar_append( GtkMenuBar *menu_bar, GtkWidget *menu_item );

which in our case looks like this:


    gtk_menu_bar_append (GTK_MENU_BAR (menu_bar), file_item);

If we wanted the menu right justified on the menubar, such as help menus often are, we can use the following function (again on file_item in the current example) before attaching it to the menubar.


void gtk_menu_item_right_justify( GtkMenuItem *menu_item );

Here is a summary of the steps needed to create a menu bar with menus attached:

Create a new menu using gtk_menu_new()
Use multiple calls to gtk_menu_item_new() for each item you wish to have on your menu. And use gtk_menu_append() to put each of these new items on to the menu.
Create a menu item using gtk_menu_item_new(). This will be the root of the menu, the text appearing here will be on the menubar itself.
Use gtk_menu_item_set_submenu() to attach the menu to the root menu item (the one created in the above step).
Create a new menubar using gtk_menu_bar_new. This step only needs to be done once when creating a series of menus on one menu bar.
Use gtk_menu_bar_append() to put the root menu onto the menubar.

Creating a popup menu is nearly the same. The difference is that the menu is not posted "automatically" by a menubar, but explicitly by calling the function gtk_menu_popup() from a button-press event, for example. Take these steps:

Create an event handling function. It needs to have the prototype
static gint handler (GtkWidget *widget, GdkEvent *event);
and it will use the event to find out where to pop up the menu.
In the event handler, if the event is a mouse button press, treat event as a button event (which it is) and use it as shown in the sample code to pass information to gtk_menu_popup().
Bind that event handler to a widget with
gtk_signal_connect_object (GTK_OBJECT (widget), "event", GTK_SIGNAL_FUNC (handler), GTK_OBJECT (menu));
where widget is the widget you are binding to, handler is the handling function, and menu is a menu created with gtk_menu_new(). This can be a menu which is also posted by a menu bar, as shown in the sample code.

13.2 Manual Menu Example

That should about do it. Let's take a look at an example to help clarify.


/* example-start menu menu.c */

#include <stdio.h>
#include <gtk/gtk.h>

static gint button_press (GtkWidget *, GdkEvent *);
static void menuitem_response (gchar *);

int main( int   argc,
          char *argv[] )
{

    GtkWidget *window;
    GtkWidget *menu;
    GtkWidget *menu_bar;
    GtkWidget *root_menu;
    GtkWidget *menu_items;
    GtkWidget *vbox;
    GtkWidget *button;
    char buf[128];
    int i;

    gtk_init (&argc, &argv);

    /* create a new window */
    window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
    gtk_widget_set_usize (GTK_WIDGET (window), 200, 100);
    gtk_window_set_title (GTK_WINDOW (window), "GTK Menu Test");
    gtk_signal_connect (GTK_OBJECT (window), "delete_event",
                        (GtkSignalFunc) gtk_main_quit, NULL);

    /* Init the menu-widget, and remember -- never
     * gtk_show_widget() the menu widget!! 
     * This is the menu that holds the menu items, the one that
     * will pop up when you click on the "Root Menu" in the app */
    menu = gtk_menu_new ();

    /* Next we make a little loop that makes three menu-entries for "test-menu".
     * Notice the call to gtk_menu_append.  Here we are adding a list of
     * menu items to our menu.  Normally, we'd also catch the "clicked"
     * signal on each of the menu items and setup a callback for it,
     * but it's omitted here to save space. */

    for (i = 0; i < 3; i++)
        {
            /* Copy the names to the buf. */
            sprintf (buf, "Test-undermenu - %d", i);

            /* Create a new menu-item with a name... */
            menu_items = gtk_menu_item_new_with_label (buf);

            /* ...and add it to the menu. */
            gtk_menu_append (GTK_MENU (menu), menu_items);

            /* Do something interesting when the menuitem is selected */
            gtk_signal_connect_object (GTK_OBJECT (menu_items), "activate",
                GTK_SIGNAL_FUNC (menuitem_response), (gpointer) g_strdup (buf));

            /* Show the widget */
            gtk_widget_show (menu_items);
        }

    /* This is the root menu, and will be the label
     * displayed on the menu bar.  There won't be a signal handler attached,
     * as it only pops up the rest of the menu when pressed. */
    root_menu = gtk_menu_item_new_with_label ("Root Menu");

    gtk_widget_show (root_menu);

    /* Now we specify that we want our newly created "menu" to be the menu
     * for the "root menu" */
    gtk_menu_item_set_submenu (GTK_MENU_ITEM (root_menu), menu);

    /* A vbox to put a menu and a button in: */
    vbox = gtk_vbox_new (FALSE, 0);
    gtk_container_add (GTK_CONTAINER (window), vbox);
    gtk_widget_show (vbox);

    /* Create a menu-bar to hold the menus and add it to our main window */
    menu_bar = gtk_menu_bar_new ();
    gtk_box_pack_start (GTK_BOX (vbox), menu_bar, FALSE, FALSE, 2);
    gtk_widget_show (menu_bar);

    /* Create a button to which to attach menu as a popup */
    button = gtk_button_new_with_label ("press me");
    gtk_signal_connect_object (GTK_OBJECT (button), "event",
        GTK_SIGNAL_FUNC (button_press), GTK_OBJECT (menu));
    gtk_box_pack_end (GTK_BOX (vbox), button, TRUE, TRUE, 2);
    gtk_widget_show (button);

    /* And finally we append the menu-item to the menu-bar -- this is the
     * "root" menu-item I have been raving about =) */
    gtk_menu_bar_append (GTK_MENU_BAR (menu_bar), root_menu);

    /* always display the window as the last step so it all splashes on
     * the screen at once. */
    gtk_widget_show (window);

    gtk_main ();

    return(0);
}

/* Respond to a button-press by posting a menu passed in as widget.
 *
 * Note that the "widget" argument is the menu being posted, NOT
 * the button that was pressed.
 */

static gint button_press( GtkWidget *widget,
                          GdkEvent *event )
{

    if (event->type == GDK_BUTTON_PRESS) {
        GdkEventButton *bevent = (GdkEventButton *) event; 
        gtk_menu_popup (GTK_MENU (widget), NULL, NULL, NULL, NULL,
                        bevent->button, bevent->time);
        /* Tell calling code that we have handled this event; the buck
         * stops here. */
        return TRUE;
    }

    /* Tell calling code that we have not handled this event; pass it on. */
    return FALSE;
}


/* Print a string when a menu item is selected */

static void menuitem_response( gchar *string )
{
    printf ("%s\n", string);
}
/* example-end */

You may also set a menu item to be insensitive and, using an accelerator table, bind keys to menu functions.

13.3 Using ItemFactory

Now that we've shown you the hard way, here's how you do it using the gtk_item_factory calls.

13.4 Item Factory Example

Here is an example using the GTK item factory.


/* example-start menu itemfactory.c */

#include <gtk/gtk.h>
#include <strings.h>

/* Obligatory basic callback */
static void print_hello( GtkWidget *w,
                         gpointer   data )
{
  g_message ("Hello, World!\n");
}

/* This is the GtkItemFactoryEntry structure used to generate new menus.
   Item 1: The menu path. The letter after the underscore indicates an
           accelerator key once the menu is open.
   Item 2: The accelerator key for the entry
   Item 3: The callback function.
   Item 4: The callback action.  This changes the parameters with
           which the function is called.  The default is 0.
   Item 5: The item type, used to define what kind of an item it is.
           Here are the possible values:

           NULL               -> "<Item>"
           ""                 -> "<Item>"
           "<Title>"          -> create a title item
           "<Item>"           -> create a simple item
           "<CheckItem>"      -> create a check item
           "<ToggleItem>"     -> create a toggle item
           "<RadioItem>"      -> create a radio item
           <path>             -> path of a radio item to link against
           "<Separator>"      -> create a separator
           "<Branch>"         -> create an item to hold sub items (optional)
           "<LastBranch>"     -> create a right justified branch 
*/

static GtkItemFactoryEntry menu_items[] = {
  { "/_File",         NULL,         NULL, 0, "<Branch>" },
  { "/File/_New",     "<control>N", print_hello, 0, NULL },
  { "/File/_Open",    "<control>O", print_hello, 0, NULL },
  { "/File/_Save",    "<control>S", print_hello, 0, NULL },
  { "/File/Save _As", NULL,         NULL, 0, NULL },
  { "/File/sep1",     NULL,         NULL, 0, "<Separator>" },
  { "/File/Quit",     "<control>Q", gtk_main_quit, 0, NULL },
  { "/_Options",      NULL,         NULL, 0, "<Branch>" },
  { "/Options/Test",  NULL,         NULL, 0, NULL },
  { "/_Help",         NULL,         NULL, 0, "<LastBranch>" },
  { "/_Help/About",   NULL,         NULL, 0, NULL },
};


void get_main_menu( GtkWidget  *window,
                    GtkWidget **menubar )
{
  GtkItemFactory *item_factory;
  GtkAccelGroup *accel_group;
  gint nmenu_items = sizeof (menu_items) / sizeof (menu_items[0]);

  accel_group = gtk_accel_group_new ();

  /* This function initializes the item factory.
     Param 1: The type of menu - can be GTK_TYPE_MENU_BAR, GTK_TYPE_MENU,
              or GTK_TYPE_OPTION_MENU.
     Param 2: The path of the menu.
     Param 3: A pointer to a gtk_accel_group.  The item factory sets up
              the accelerator table while generating menus.
  */

  item_factory = gtk_item_factory_new (GTK_TYPE_MENU_BAR, "<main>", 
                                       accel_group);

  /* This function generates the menu items. Pass the item factory,
     the number of items in the array, the array itself, and any
     callback data for the the menu items. */
  gtk_item_factory_create_items (item_factory, nmenu_items, menu_items, NULL);

  /* Attach the new accelerator group to the window. */
  gtk_window_add_accel_group (GTK_WINDOW (window), accel_group);

  if (menubar)
    /* Finally, return the actual menu bar created by the item factory. */ 
    *menubar = gtk_item_factory_get_widget (item_factory, "<main>");
}

int main( int argc,
          char *argv[] )
{
  GtkWidget *window;
  GtkWidget *main_vbox;
  GtkWidget *menubar;
  
  gtk_init (&argc, &argv);
  
  window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
  gtk_signal_connect (GTK_OBJECT (window), "destroy", 
                      GTK_SIGNAL_FUNC (gtk_main_quit), 
                      "WM destroy");
  gtk_window_set_title (GTK_WINDOW(window), "Item Factory");
  gtk_widget_set_usize (GTK_WIDGET(window), 300, 200);
  
  main_vbox = gtk_vbox_new (FALSE, 1);
  gtk_container_border_width (GTK_CONTAINER (main_vbox), 1);
  gtk_container_add (GTK_CONTAINER (window), main_vbox);
  gtk_widget_show (main_vbox);
  
  get_main_menu (window, &menubar);
  gtk_box_pack_start (GTK_BOX (main_vbox), menubar, FALSE, TRUE, 0);
  gtk_widget_show (menubar);
  
  gtk_widget_show (window);
  gtk_main ();
  
  return(0);
}
/* example-end */

For now, there's only this example. An explanation and lots 'o' comments will follow later.

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