This chapter contains some tutorial information to get you started with GTK+ programming. It assumes that you have GTK+, its dependencies and a C compiler installed and ready to use. If you need to build GTK+ itself first, refer to the Compiling the GTK+ libraries section in this reference.

To begin our introduction to GTK, we'll start with the simplest program possible. This program will create an empty 200 × 200 pixel window. Create a new file with the following content named example-0.c. FIXME: MISSING XINCLUDE CONTENT You can compile the program above with GCC using: gcc `pkg-config --cflags gtk+-3.0` -o example-0 example-0.c `pkg-config --libs gtk+-3.0` For more information on how to compile a GTK+ application, please refer to the Compiling GTK+ Applications section in this reference. All GTK+ applications will, of course, include gtk/gtk.h, which declares functions, types and macros required by GTK+ applications. Even if GTK+ installs multiple header files, only the top-level gtk/gtk.h header can be directly included by third party code. The compiler will abort with an error if any other header is directly included. We then proceed into the main() function of the application, and we declare a window variable as a pointer of type #GtkWidget. The following line will call gtk_init(), which is the initialization function for GTK+; this function will set up GTK+, the type system, the connection to the windowing environment, etc. The gtk_init() takes as arguments the pointers to the command line arguments counter and string array; this allows GTK+ to parse specific command line arguments that control the behavior of GTK+ itself. The parsed arguments will be removed from the array, leaving the unrecognized ones for your application to parse. For more information on which command line arguments GTK+ recognizes, please refer to the Running GTK+ Applications section in this reference. The call to gtk_window_new() will create a new #GtkWindow and store it inside the window variable. The type of the window is %GTK_WINDOW_TOPLEVEL, which means that the #GtkWindow will be managed by the windowing system: it will have a frame, a title bar and window controls, depending on the platform. In order to terminate the application when the #GtkWindow is destroyed, we connect the #GtkWidget::destroy signal to the gtk_main_quit() function. This function will terminate the GTK+ main loop started by calling gtk_main() later. The #GtkWidget::destroy signal is emitted when a widget is destroyed, either by explicitly calling gtk_widget_destroy() or when the widget is unparented. Top-level #GtkWindows are also destroyed when the Close window control button is clicked. #GtkWidgets are hidden by default. By calling gtk_widget_show() on a #GtkWidget we are asking GTK+ to set the visibility attribute so that it can be displayed. All this work is done after the main loop has been started. The last line of interest is the call to gtk_main(). This function will start the GTK+ main loop and will block the control flow of the main() until the gtk_main_quit() function is called. While the program is running, GTK+ is receiving events. These are typically input events caused by the user interacting with your program, but also things like messages from the window manager or other applications. GTK+ processes these and as a result, signals may be emitted on your widgets. Connecting handlers for these signals is how you normally make your program do something in response to user input. The following example is slightly more complex, and tries to showcase some of the capabilities of GTK+. In the long tradition of programming languages and libraries, it is called Hello, World. Create a new file with the following content named example-1.c. FIXME: MISSING XINCLUDE CONTENT You can compile the program above with GCC using: gcc `pkg-config --cflags gtk+-3.0` -o example-1 example-1.c `pkg-config --libs gtk+-3.0`

When creating an application, you'll want to put more than one widget inside a window. Our first helloworld example only used one widget so we could simply use a gtk_container_add() call to "pack" the widget into the window. But when you want to put more than one widget into a window, it it becomes important to control how each widget is positioned and sized. This is where packing comes in. GTK+ comes with a large variety of layout containers whose purpose it is to control the layout of the child widgets that are added to them. See for an overview. The following example shows how the GtkGrid container lets you arrange several buttons: Create a new file with the following content named example-2.c. FIXME: MISSING XINCLUDE CONTENT You can compile the program above with GCC using: gcc `pkg-config --cflags gtk+-3.0` -o example-2 example-2.c `pkg-config --libs gtk+-3.0`

Many widgets, like buttons, do all their drawing themselves. You just tell them the label you want to see, and they figure out what font to use, draw the button outline and focus rectangle, etc. Sometimes, it is necessary to do some custom drawing. In that case, a #GtkDrawingArea might be the right widget to use. It offers a canvas on which you can draw by connecting to the #GtkWidget::draw signal. The contents of a widget often need to be partially or fully redrawn, e.g. when another window is moved and uncovers part of the widget, or when tie window containing it is resized. It is also possible to explicitly cause part or all of the widget to be redrawn, by calling gtk_widget_queue_draw() or its variants. GTK+ takes care of most of the details by providing a ready-to-use cairo context to the ::draw signal handler. The following example shows a ::draw signal handler. It is a bit more complicated than the previous examples, since it also demonstrates input event handling by means of ::button-press and ::motion-notify handlers. Create a new file with the following content named example-3.c. FIXME: MISSING XINCLUDE CONTENT You can compile the program above with GCC using: gcc `pkg-config --cflags gtk+-3.0` -o example-3 example-3.c `pkg-config --libs gtk+-3.0`

When construcing a more complicated user interface, with dozens or hundreds of widgets, doing all the setup work in C code is cumbersome, and making changes becomes next to impossible. Thankfully, GTK+ supports the separation of user interface layout from your business logic, by using UI descriptions in an XML format that can be parsed by the #GtkBuilder class. Create a new file with the following content named example-4.c. FIXME: MISSING XINCLUDE CONTENT Create a new file with the following content named builder.ui. FIXME: MISSING XINCLUDE CONTENT You can compile the program above with GCC using: gcc `pkg-config --cflags gtk+-3.0` -o example-4 example-4.c `pkg-config --libs gtk+-3.0` Note that GtkBuilder can also be used to construct objects that are not widgets, such as tree models, adjustments, etc. That is the reason the method we use here is called gtk_builder_get_object() and returns a GObject* instead of a GtkWidget*. Normally, you would pass a full path to gtk_builder_add_from_file() to make the execution of your program independent of the current directory. A common location to install UI descriptions and similar data is /usr/share/appname. It is also possible to embed the UI description in the source code as a string and use gtk_builder_add_from_string() to load it. But keeping the UI description in a separate file has several advantages: It is then possible to make minor adjustments to the UI without recompiling your program, and, more importantly, graphical UI editors such as glade can load the file and allow you to create and modify your UI by point-and-click.

An application consists of a number of files: The binary This gets installed in /usr/bin. A desktop file The desktop file provides important information about the application to the desktop shell, such as its name, icon, D-Bus name, commandline to launch it, etc. It is installed in /usr/share/applications. An icon The icon gets installed in /usr/share/icons/hicolor/48x48/apps, where it will be found regardless of the current theme. A settings schema If the application uses GSettings, it will install its schema in /usr/share/glib-2.0/schemas, so that tools like dconf-editor can find it. Other resources Other files, such as GtkBuilder ui files, are best loaded from resources stored in the application binary itself. This eliminates the need for most of the files that would traditionally be installed in an application-specific location in /usr/share. GTK+ includes application support that is built on top of #GApplication. In this tutorial we'll build a simple application by starting from scratch, adding more and more pieces over time. Along the way, we'll learn about #GtkApplication, templates, resources, application menus, settings, #GtkHeaderBar, #GtkStack, #GtkSearchBar, #GtkListBox, and more. The full, buildable sources for these examples can be found in the examples/ directory of the GTK+ source distribution, or online in the GTK+ git repository.

When using #GtkApplication, the main() function can be very simple. We just call g_application_run() and give it an instance of our application class. FIXME: MISSING XINCLUDE CONTENT All the application logic is in the application class, which is a subclass of #GtkApplication. Our example does not yet have any interesting functionality. All it does is open a window when it is activated without arguments, and open the files it is given, if it is started with arguments. To handle these two cases, we override the activate() vfunc, which gets called when the application is launched without commandline arguments, and the open() vfunc, which gets called when the application is launched with commandline arguments. To learn more about GApplication entry points, consult the GIO documentation. FIXME: MISSING XINCLUDE CONTENT Another important class that is part of the application support in GTK+ is #GtkApplicationWindow. It is typically subclassed as well. Our subclass does not do anything yet, so we will just get an empty window. FIXME: MISSING XINCLUDE CONTENT As part of the initial setup of our application, we also create an icon and a desktop file. FIXME: MISSING XINCLUDE CONTENT Note that @bindir@ needs to be replaced with the actual path to the binary before this desktop file can be used. Here is what we've achieved so far: This does not look very impressive yet, but our application is already presenting itself on the session bus, it has single-instance semantics, and it accepts files as commandline arguments.

In this step, we use a #GtkBuilder template to associate a #GtkBuilder ui file with our application window class. Our simple ui file puts a #GtkHeaderBar on top of a #GtkStack widget. The header bar contains a #GtkStackSwitcher, which is a standalone widget to show a row of 'tabs' for the pages of a #GtkStack. FIXME: MISSING XINCLUDE CONTENT To make use of this file in our application, we revisit our #GtkApplicationWindow subclass, and call gtk_widget_class_set_template_from_resource() from the class init function to set the ui file as template for this class. We also add a call to gtk_widget_init_template() in the instance init function to instantiate the template for each instance of our class. (full source) You may have noticed that we used the _from_resource() variant of the function that sets a template. Now we need to use GLib's resource functionality to include the ui file in the binary. This is commonly done by listing all resources in a .gresource.xml file, such as this: FIXME: MISSING XINCLUDE CONTENT This file has to be converted into a C source file that will be compiled and linked into the application together with the other source files. To do so, we use the glib-compile-resources utility: glib-compile-resources exampleapp.gresource.xml --target=resources.c --generate-source Our application now looks like this:

In this step, we make our application show the content of all the files that it is given on the commandline. To this end, we add a private struct to our application window subclass and keep a reference to the #GtkStack there. The gtk_widget_class_bind_template_child_private() function arranges things so that after instantiating the template, the @stack member of the private struct will point to the widget of the same name from the template. (full source) Now we revisit the example_app_window_open() function that is called for each commandline argument, and construct a GtkTextView that we then add as a page to the stack: stack), scrolled, basename, basename); if (g_file_load_contents (file, NULL, &contents, &length, NULL, NULL)) { GtkTextBuffer *buffer; buffer = gtk_text_view_get_buffer (GTK_TEXT_VIEW (view)); gtk_text_buffer_set_text (buffer, contents, length); g_free (contents); } g_free (basename); } ... ]]> (full source) Note that we did not have to touch the stack switcher at all. It gets all its information from the stack that it belongs to. Here, we are passing the label to show for each file as the last argument to the gtk_stack_add_titled() function. Our application is beginning to take shape:

An application menu is shown by GNOME shell at the top of the screen. It is meant to collect infrequently used actions that affect the whole application. Just like the window template, we specify our application menu in a ui file, and add it as a resource to our binary. FIXME: MISSING XINCLUDE CONTENT To associate the app menu with the application, we have to call gtk_application_set_app_menu(). Since app menus work by activating #GActions, we also have to add a suitable set of actions to our application. Both of these tasks are best done in the startup() vfunc, which is guaranteed to be called once for each primary application instance: ... static void preferences_activated (GSimpleAction *action, GVariant *parameter, gpointer app) { } static void quit_activated (GSimpleAction *action, GVariant *parameter, gpointer app) { g_application_quit (G_APPLICATION (app)); } static GActionEntry app_entries[] = { { "preferences", preferences_activated, NULL, NULL, NULL }, { "quit", quit_activated, NULL, NULL, NULL } }; static void example_app_startup (GApplication *app) { GtkBuilder *builder; GMenuModel *app_menu; G_APPLICATION_CLASS (example_app_parent_class)->startup (app); g_action_map_add_action_entries (G_ACTION_MAP (app), app_entries, G_N_ELEMENTS (app_entries), app); builder = gtk_builder_new_from_resource ("/org/gtk/exampleapp/app-menu.ui"); app_menu = G_MENU_MODEL (gtk_builder_get_object (builder, "appmenu")); gtk_application_set_app_menu (GTK_APPLICATION (app), app_menu); g_object_unref (builder); } static void example_app_class_init (ExampleAppClass *class) { G_APPLICATION_CLASS (class)->startup = example_app_startup; ... } ... (full source) Our preferences menu item does not do anything yet, but the Quit menu item is fully functional. Note that it can also be activated by the usual Ctrl-Q shortcut. The shortcut was specified in the ui file. The application menu looks like this:

A typical application will have a some preferences that should be remembered from one run to the next. Even for our simple example application, we may want to change the font that is used for the content. We are going to use GSettings to store our preferences. GSettings requires a schema that describes our settings: FIXME: MISSING XINCLUDE CONTENT Before we can make use of this schema in our application, we need to compile it into the binary form that GSettings expects. GIO provides macros to do this in autotools-based projects. Next, we need to connect our settings to the widgets that they are supposed to control. One convenient way to do this is to use GSettings bind functionality to bind settings keys to object properties, as we do here for the transition setting. settings = g_settings_new ("org.gtk.exampleapp"); g_settings_bind (priv->settings, "transition", priv->stack, "transition-type", G_SETTINGS_BIND_DEFAULT); } ... ]]> (full source) The code to connect the font setting is a little more involved, since there is no simple object property that it corresponds to, so we are not going to go into that here. At this point, the application will already react if you change one of the settings, e.g. using the gsettings commandline tool. Of course, we expect the application to provide a preference dialog for these. So lets do that now. Our preference dialog will be a subclass of GtkDialog, and we'll use the same techniques that we've already seen: templates, private structs, settings bindings. Lets start with the template. FIXME: MISSING XINCLUDE CONTENT Next comes the dialog subclass. FIXME: MISSING XINCLUDE CONTENT Now we revisit the preferences_activated() function in our application class, and make it open a new preference dialog. (full source) After all this work, our application can now show a preference dialog like this:

We continue to flesh out the functionality of our application. For now, we add search. GTK+ supports this with #GtkSearchEntry and #GtkSearchBar. The search bar is a widget that can slide in from the top to present a search entry. We add a toggle button to the header bar, which can be used to slide out the search bar below the header bar. FIXME: MISSING XINCLUDE CONTENT Implementing the search needs quite a few code changes that we are not going to completely go over here. The central piece of the search implementation is a signal handler that listens for text changes in the search entry. stack)); view = gtk_bin_get_child (GTK_BIN (tab)); buffer = gtk_text_view_get_buffer (GTK_TEXT_VIEW (view)); /* Very simple-minded search implementation */ gtk_text_buffer_get_start_iter (buffer, &start); if (gtk_text_iter_forward_search (&start, text, GTK_TEXT_SEARCH_CASE_INSENSITIVE, &match_start, &match_end, NULL)) { gtk_text_buffer_select_range (buffer, &match_start, &match_end); gtk_text_view_scroll_to_iter (GTK_TEXT_VIEW (view), &match_start, 0.0, FALSE, 0.0, 0.0); } } static void example_app_window_init (ExampleAppWindow *win) { ... gtk_widget_class_bind_template_callback (GTK_WIDGET_CLASS (class), search_text_changed); ... } ... ]]> (full source) With the search bar, our application now looks like this:

As another piece of functionality, we are adding a sidebar, which demonstrates #GtkMenuButton, #GtkRevealer and #GtkListBox. FIXME: MISSING XINCLUDE CONTENT The code to populate the sidebar with buttons for the words found in each file is a little too involved to go into here. But we'll look at the code to add the gears menu. As expected by now, the gears menu is specified in a GtkBuilder ui file. FIXME: MISSING XINCLUDE CONTENT To connect the menuitem to the show-words setting, we use a #GAction corresponding to the given #GSettings key. gears), menu); g_object_unref (builder); action = g_settings_create_action (priv->settings, "show-words"); g_action_map_add_action (G_ACTION_MAP (win), action); g_object_unref (action); } ... ]]> (full source) What our application looks like now:

Widgets and other objects have many useful properties. Here we show some ways to use them in new and flexible ways, by wrapping them in actions with #GPropertyAction or by binding them with #GBinding. To set this up, we add two labels to the header bar in our window template, named @lines_label and @lines, and bind them to struct members in the private struct, as we've seen a couple of times by now. We add a new "Lines" menu item to the gears menu, which triggers the show-lines action: FIXME: MISSING XINCLUDE CONTENT To make this menu item do something, we create a property action for the visible property of the @lines label, and add it to the actions of the window. The effect of this is that the visibility of the label gets toggled every time the action is activated. Since we want both labels to appear and disappear together, we bind the visible property of the @lines_label widget to the same property of the @lines widget. ... static void example_app_window_init (ExampleAppWindow *win) { ... action = (GAction*) g_property_action_new ("show-lines", priv->lines, "visible"); g_action_map_add_action (G_ACTION_MAP (win), action); g_object_unref (action); g_object_bind_property (priv->lines, "visible", priv->lines_label, "visible", G_BINDING_DEFAULT); } ... (full source) We also need a function that counts the lines of the currently active tab, and updates the @lines label. See the full source if you are interested in the details. This brings our example application to this appearance:

Our application already uses a GtkHeaderBar, but so far it still gets a 'normal' window titlebar on top of that. This is a bit redundant, and we will now tell GTK+ to use the header bar as replacement for the titlebar. To do so, we move it around to be a direct child of the window, and set its type to be titlebar. FIXME: MISSING XINCLUDE CONTENT A small extra refinement that we have added here is to allow the header bar to provide a fallback application menu, by setting the show-fallback-app-menu property to TRUE. Here is how the application now looks, if this fallback is used. If we set up the window icon for our window, the menu button will use that instead of the generic placeholder icon you see here.