<?xml version="1.0"?>
<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
"http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd" [
]>
<chapter id="gtk-getting-started" xmlns:xi="http://www.w3.org/2003/XInclude">
<title>Getting Started with GTK+</title>
<para>GTK+ is a <ulink url="http://en.wikipedia.org/wiki/Widget_toolkit">
widget toolkit</ulink>. Each user interface created by
GTK+ consists of widgets. This is implemented in C using
<link linkend="gobject">GObject</link>, an object-oriented framework for C.
Widgets are organized in a hierachy. The window widget is the main container.
The user interface is then built by adding buttons, drop-down menus, input
fields, and other widgets to the window.
If you are creating complex user interfaces it is recommended to
use #GtkBuilder and its GTK-specific markup description language, instead of
assembling the interface manually. You can also use a visual user interface
editor, like <ulink url="https://glade.gnome.org/">Glade</ulink>.</para>
<para>GTK+ is event-driven. The toolkit listens for events such as
a click on a button, and passes the event to your application.</para>
<para>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
<link linkend="gtk-compiling">Compiling the GTK+ libraries</link>
section in this reference.</para>
<section>
<title>Basics</title>
<para>To begin our introduction to GTK, we'll start with a simple
signal-based Gtk application. This program will create an empty 200 × 200 pixel
window.</para>
<informalfigure>
<mediaobject>
<imageobject>
<imagedata fileref="window-default.png" format="PNG"/>
</imageobject>
</mediaobject>
</informalfigure>
<informalexample>
<para>Create a new file with the following content named <filename>example-0.c.</filename></para>
<programlisting><xi:include href="@abs_top_srcdir@/examples/window-default.c" parse="text"><xi:fallback>MISSING XINCLUDE CONTENT</xi:fallback></xi:include></programlisting>
</informalexample>
<para>
You can compile the program above with GCC using:
<literallayout>
<literal>gcc `pkg-config --cflags gtk+-3.0` -o example-0 example-0.c `pkg-config --libs gtk+-3.0`</literal>
</literallayout>
</para>
<note><para>For more information on how to compile a GTK+ application, please
refer to the <link linkend="gtk-compiling">Compiling GTK+ Applications</link>
section in this reference.</para></note>
<para>All GTK+ applications will, of course, include
<filename>gtk/gtk.h</filename>, which declares functions, types and
macros required by GTK+ applications.</para>
<warning><para>Even if GTK+ installs multiple header files, only the
top-level <filename>gtk/gtk.h</filename> header can be directly included
by third party code. The compiler will abort with an error if any other
header is directly included.</para></warning>
<para>In a GTK+ application, the purpose of the main() function is to
create a #GtkApplication object and run it. In this example a
#GtkApplication pointer named <varname>app</varname> is called and then
initialized using gtk_application_new().</para>
<para>When creating a #GtkApplication
you need to pick an application identifier (a name)
and input to gtk_application_new() as parameter.
For this example <varname>org.gtk.example</varname> is used
but for choosing an identifier for your application see
<ulink url="https://wiki.gnome.org/HowDoI/ChooseApplicationID">this guide</ulink>.
Lastly gtk_application_new() takes a GApplicationFlags as input for your
application, if your application would have special needs.
</para>
<para>Next the
<ulink url="https://wiki.gnome.org/HowDoI/GtkApplication">activate signal</ulink>
is connected to the activate() function above the main() functions.
The <varname>activate</varname> signal will be sent
when your application is launched with
g_application_run() on the line below.
The gtk_application_run() also 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.
</para>
<para>Within g_application_run the activate() signal is sent and
we then proceed into the <function>activate</function>() function of the
application. Inside the activate() function we want to construct
our GTK window, so that a window is shown when the application
is launched. The call to gtk_application_window_new() will
create a new #GtkWindow and store it inside the
<varname>window</varname> pointer. The window will have a frame,
a title bar, and window controls depending on the platform.</para>
<para>A window title is set using gtk_window_set_title(). This function
takes a GtkWindow* pointer and a string as input. As our
<varname>window</varname> pointer is a GtkWidget pointer, we need to cast it
to GtkWindow*.
But instead of casting <varname>window</varname> via
<varname>(GtkWindow*)</varname>,
<varname>window</varname> can be cast using the macro
<varname>GTK_WINDOW()</varname>.
<varname>GTK_WINDOW()</varname> will check if the
pointer is an instance of the GtkWindow class, before casting, and emit a
warning if the check fails. More information about this convention
can be found
<ulink url="https://developer.gnome.org/gobject/stable/gtype-conventions.html">
here</ulink>.</para>
<para>Finally the window size is set using gtk_window_set_default_size and
the window is then shown by GTK via gtk_widget_show_all().</para>
<para>When you exit the window, by for example pressing the X,
the g_application_run() in the main loop returns with a number
which is saved inside an integer named "status". Afterwards, the
#GtkApplication object is freed from memory with g_object_unref().
Finally the status integer is returned and the GTK application exits.</para>
<para>While the program is running, GTK+ is receiving
<firstterm>events</firstterm>. 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, <firstterm>signals</firstterm> 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.</para>
<para>The following example is slightly more complex, and tries to
showcase some of the capabilities of GTK+.</para>
<para>In the long tradition of programming languages and libraries,
it is called <emphasis>Hello, World</emphasis>.</para>
<informalfigure>
<mediaobject>
<imageobject>
<imagedata fileref="hello-world.png" format="PNG"/>
</imageobject>
</mediaobject>
</informalfigure>
<example id="gtk-getting-started-hello-world">
<title>Hello World in GTK+</title>
<para>Create a new file with the following content named example-1.c.</para>
<programlisting><xi:include href="@abs_top_srcdir@/examples/hello-world.c" parse="text">
<xi:fallback>MISSING XINCLUDE CONTENT</xi:fallback></xi:include></programlisting>
</example>
<para>
You can compile the program above with GCC using:
<literallayout>
<literal>gcc `pkg-config --cflags gtk+-3.0` -o example-1 example-1.c `pkg-config --libs gtk+-3.0`</literal>
</literallayout>
</para>
</section>
<para>As seen above, example-1.c builds further upon example-0.c by adding a
button to our window, with the label "Hello World". Two new GtkWidget pointers
are declared to accomplish this, <varname>button</varname> and
<varname>button_box</varname>. The button_box variable is created to store a
#GtkButtonBox which is GTK+'s way of controlling the size and layout of buttons.
The #GtkButtonBox is created and assigned to gtk_button_box_new() which takes a
#GtkOrientation enum as parameter. The buttons which this box will contain can
either be stored horizontally or vertically but this does not matter in this
particular case as we are dealing with only one button. After initializing
button_box with horizontal orientation, the code adds the button_box widget to the
window widget using gtk_container_add().</para>
<para>Next the <varname>button</varname> variable is initialized in similar manner.
gtk_button_new_with_label() is called which returns a GtkButton to be stored inside
<varname>button</varname>. Afterwards <varname>button</varname> is added to
our <varname>button_box</varname>.
Using g_signal_connect the button is connected to a function in our app called
print_hello(), so that when the button is clicked, GTK will call this function.
As the print_hello() function does not use any data as input, NULL is passed
to it. print_hello() calls g_print() with the string "Hello World"
which will print Hello World in a terminal if the GTK application was started
from one.</para>
<para>After connecting print_hello(), another signal is connected to the "clicked" state
of the button using g_signal_connect_swapped(). This functions is similar to
a g_signal_connect() with the difference lying in how the callback function is
treated. g_signal_connect_swapped() allow you to specify what the callback
function should take as parameter by letting you pass it as data. In this case
the function being called back is gtk_widget_destroy() and the <varname>window</varname>
pointer is passed to it. This has the effect that when the button is clicked,
the whole GTK window is destroyed. In contrast if a normal g_signal_connect() were used
to connect the "clicked" signal with gtk_widget_destroy(), then the <varname>button</varname>
itself would have been destroyed, not the window.
More information about creating buttons can be found
<ulink url="https://wiki.gnome.org/HowDoI/Buttons">here</ulink>.
</para>
<para>The rest of the code in example-1.c is identical to example-0.c. Next
section will elaborate further on how to add several GtkWidgets to your GTK
application.</para>
<section>
<title>Packing</title>
<para>When creating an application, you'll want to put more than one widget
inside a window.
When you want to put more than one widget into a window,
it becomes important to control how each widget is positioned and sized.
This is where packing comes in.</para>
<para>GTK+ comes with a large variety of <firstterm>layout containers</firstterm>
whose purpose it is to control the layout of the child widgets that are
added to them. See <xref linkend="LayoutContainers"/> for an overview.</para>
<para>The following example shows how the GtkGrid container lets you
arrange several buttons:</para>
<informalfigure>
<mediaobject>
<imageobject>
<imagedata fileref="grid-packing.png" format="PNG"/>
</imageobject>
</mediaobject>
</informalfigure>
<example id="gtk-getting-started-grid-packing">
<title>Packing buttons</title>
<para>Create a new file with the following content named example-2.c.</para>
<programlisting><xi:include href="@abs_top_srcdir@/examples/grid-packing.c" parse="text"><xi:fallback>MISSING XINCLUDE CONTENT</xi:fallback></xi:include></programlisting>
</example>
<para>
You can compile the program above with GCC using:
<literallayout>
<literal>gcc `pkg-config --cflags gtk+-3.0` -o example-2 example-2.c `pkg-config --libs gtk+-3.0`</literal>
</literallayout>
</para>
</section>
<section>
<title>Building user interfaces</title>
<para>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.</para>
<para>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.</para>
<example>
<title>Packing buttons with GtkBuilder</title>
<para>Create a new file with the following content named example-3.c.</para>
<programlisting><xi:include href="@abs_top_srcdir@/examples/builder.c" parse="text"><xi:fallback>MISSING XINCLUDE CONTENT</xi:fallback></xi:include></programlisting>
<para>Create a new file with the following content named builder.ui.</para>
<programlisting><xi:include href="@abs_top_srcdir@/examples/builder.ui" parse="text"><xi:fallback>MISSING XINCLUDE CONTENT</xi:fallback></xi:include></programlisting>
</example>
<para>
You can compile the program above with GCC using:
<literallayout>
<literal>gcc `pkg-config --cflags gtk+-3.0` -o example-3 example-3.c `pkg-config --libs gtk+-3.0`</literal>
</literallayout>
</para>
<para>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*.</para>
<para>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
<filename>/usr/share/<replaceable>appname</replaceable></filename>.
</para>
<para>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 <ulink url="http://glade.gnome.org">glade</ulink>
can load the file and allow you to create and modify your UI by
point-and-click.</para>
</section>
<section>
<title>Building applications</title>
<para>An application consists of a number of files:
<variablelist>
<varlistentry>
<term>The binary</term>
<listitem>This gets installed in <filename>/usr/bin</filename>.</listitem>
</varlistentry>
<varlistentry>
<term>A desktop file</term>
<listitem>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 <filename>/usr/share/applications</filename>.</listitem>
</varlistentry>
<varlistentry>
<term>An icon</term>
<listitem>The icon gets installed in <filename>/usr/share/icons/hicolor/48x48/apps</filename>, where it will be found regardless of the current theme.</listitem>
</varlistentry>
<varlistentry>
<term>A settings schema</term>
<listitem>If the application uses GSettings, it will install its schema
in <filename>/usr/share/glib-2.0/schemas</filename>, so that tools
like dconf-editor can find it.</listitem>
</varlistentry>
<varlistentry>
<term>Other resources</term>
<listitem>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 <filename>/usr/share</filename>.</listitem>
</varlistentry>
</variablelist>
</para>
<para>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.</para>
<para>The full, buildable sources for these examples can be found
in the examples/ directory of the GTK+ source distribution, or
<ulink url="https://git.gnome.org/browse/gtk+/tree/examples">online</ulink> in the GTK+ git repository.
You can build each example separately by using make with the <filename>Makefile.example</filename>
file. For more information, see the <filename>README</filename> included in the
examples directory.</para>
<section>
<title>A trivial application</title>
<para>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.</para>
<informalexample>
<programlisting><xi:include href="@abs_top_srcdir@/examples/application1/main.c" parse="text"><xi:fallback>MISSING XINCLUDE CONTENT</xi:fallback></xi:include></programlisting>
</informalexample>
<para>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.</para>
<para>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.</para>
<para>To learn more about GApplication entry points, consult the
GIO <ulink url="https://developer.gnome.org/gio/2.36/GApplication.html#GApplication.description">documentation</ulink>.</para>
<informalexample>
<programlisting><xi:include href="@abs_top_srcdir@/examples/application1/exampleapp.c" parse="text"><xi:fallback>MISSING XINCLUDE CONTENT</xi:fallback></xi:include></programlisting>
</informalexample>
<para>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.</para>
<informalexample>
<programlisting><xi:include href="@abs_top_srcdir@/examples/application1/exampleappwin.c" parse="text"><xi:fallback>MISSING XINCLUDE CONTENT</xi:fallback></xi:include></programlisting>
</informalexample>
<para>As part of the initial setup of our application, we also
create an icon and a desktop file.</para>
<informalfigure>
<mediaobject>
<imageobject>
<imagedata fileref="exampleapp.png" format="PNG"/>
</imageobject>
</mediaobject>
</informalfigure>
<informalexample>
<programlisting><xi:include href="@abs_top_srcdir@/examples/application1/exampleapp.desktop" parse="text"><xi:fallback>MISSING XINCLUDE CONTENT</xi:fallback></xi:include></programlisting>
</informalexample>
<para>Note that <replaceable>@<!-- -->bindir@</replaceable> needs to be replaced
with the actual path to the binary before this desktop file can be used.</para>
<para>Here is what we've achieved so far:</para>
<informalfigure>
<mediaobject>
<imageobject>
<imagedata fileref="getting-started-app1.png" format="PNG"/>
</imageobject>
</mediaobject>
</informalfigure>
<para>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.</para>
</section>
<section>
<title>Populating the window</title>
<para>In this step, we use a #GtkBuilder template to associate a
#GtkBuilder ui file with our application window class.</para>
<para>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.
</para>
<informalexample>
<programlisting><xi:include href="@abs_top_srcdir@/examples/application2/window.ui" parse="text"><xi:fallback>MISSING XINCLUDE CONTENT</xi:fallback></xi:include></programlisting>
</informalexample>
<para>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.</para>
<informalexample>
<programlisting><![CDATA[
...
static void
example_app_window_init (ExampleAppWindow *win)
{
gtk_widget_init_template (GTK_WIDGET (win));
}
static void
example_app_window_class_init (ExampleAppWindowClass *class)
{
gtk_widget_class_set_template_from_resource (GTK_WIDGET_CLASS (class),
"/org/gtk/exampleapp/window.ui");
}
...
]]></programlisting>
<para>(<ulink url="https://gitlab.gnome.org/GNOME/gtk/blob/gtk-3-22/examples/application2/exampleappwin.c">full source</ulink>)</para>
</informalexample>
<para>You may have noticed that we used the <literal>_from_resource(<!-- -->)</literal> variant
of the function that sets a template. Now we need to use <ulink url="https://developer.gnome.org/gio/stable/GResource.html">GLib's resource functionality</ulink>
to include the ui file in the binary. This is commonly done by listing
all resources in a .gresource.xml file, such as this:
</para>
<informalexample>
<programlisting><xi:include href="@abs_top_srcdir@/examples/application2/exampleapp.gresource.xml" parse="text"><xi:fallback>MISSING XINCLUDE CONTENT</xi:fallback></xi:include></programlisting>
</informalexample>
<para>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:</para>
<screen>
glib-compile-resources exampleapp.gresource.xml --target=resources.c --generate-source
</screen>
<para>Our application now looks like this:</para>
<informalfigure>
<mediaobject>
<imageobject>
<imagedata fileref="getting-started-app2.png" format="PNG"/>
</imageobject>
</mediaobject>
</informalfigure>
</section>
<section>
<title>Opening files</title>
<para>In this step, we make our application show the content of
all the files that it is given on the commandline.</para>
<para>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.</para>
<informalexample>
<programlisting><![CDATA[
...
struct _ExampleAppWindowPrivate
{
GtkWidget *stack;
};
G_DEFINE_TYPE_WITH_PRIVATE(ExampleAppWindow, example_app_window, GTK_TYPE_APPLICATION_WINDOW);
...
static void
example_app_window_class_init (ExampleAppWindowClass *class)
{
gtk_widget_class_set_template_from_resource (GTK_WIDGET_CLASS (class),
"/org/gtk/exampleapp/window.ui");
gtk_widget_class_bind_template_child_private (GTK_WIDGET_CLASS (class), ExampleAppWindow, stack);
}
...
]]></programlisting>
<para>(<ulink url="https://gitlab.gnome.org/GNOME/gtk/blob/gtk-3-22/examples/application3/exampleappwin.c">full source</ulink>)</para>
</informalexample>
<para>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:</para>
<informalexample>
<programlisting><![CDATA[
...
void
example_app_window_open (ExampleAppWindow *win,
GFile *file)
{
ExampleAppWindowPrivate *priv;
gchar *basename;
GtkWidget *scrolled, *view;
gchar *contents;
gsize length;
priv = example_app_window_get_instance_private (win);
basename = g_file_get_basename (file);
scrolled = gtk_scrolled_window_new (NULL, NULL);
gtk_widget_show (scrolled);
gtk_widget_set_hexpand (scrolled, TRUE);
gtk_widget_set_vexpand (scrolled, TRUE);
view = gtk_text_view_new ();
gtk_text_view_set_editable (GTK_TEXT_VIEW (view), FALSE);
gtk_text_view_set_cursor_visible (GTK_TEXT_VIEW (view), FALSE);
gtk_widget_show (view);
gtk_container_add (GTK_CONTAINER (scrolled), view);
gtk_stack_add_titled (GTK_STACK (priv->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);
}
...
]]></programlisting>
<para>(<ulink url="https://gitlab.gnome.org/GNOME/gtk/blob/gtk-3-22/examples/application3/exampleappwin.c">full source</ulink>)</para>
</informalexample>
<para>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.</para>
<para>Our application is beginning to take shape:</para>
<informalfigure>
<mediaobject>
<imageobject>
<imagedata fileref="getting-started-app3.png" format="PNG"/>
</imageobject>
</mediaobject>
</informalfigure>
</section>
<section>
<title>An application menu</title>
<para>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.</para>
<para>Just like the window template, we specify our application menu
in a ui file, and add it as a resource to our binary.</para>
<informalexample>
<programlisting><xi:include href="@abs_top_srcdir@/examples/application4/app-menu.ui" parse="text"><xi:fallback>MISSING XINCLUDE CONTENT</xi:fallback></xi:include></programlisting>
</informalexample>
<para>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.</para>
<para>Both of these tasks are best done in the startup() vfunc,
which is guaranteed to be called once for each primary application
instance:</para>
<informalexample>
<programlisting>
...
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;
const gchar *quit_accels[2] = { "<Ctrl>Q", NULL };
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);
gtk_application_set_accels_for_action (GTK_APPLICATION (app),
"app.quit",
quit_accels);
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;
...
}
...
</programlisting>
<para>(<ulink url="https://gitlab.gnome.org/GNOME/gtk/blob/gtk-3-22/examples/application4/exampleapp.c">full source</ulink>)</para>
</informalexample>
<para>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 added with gtk_application_set_accels_for_action().
</para>
<para>The application menu looks like this:</para>
<informalfigure>
<mediaobject>
<imageobject>
<imagedata fileref="getting-started-app4.png" format="PNG"/>
</imageobject>
</mediaobject>
</informalfigure>
</section>
<section>
<title>A preference dialog</title>
<para>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.</para>
<para>We are going to use GSettings to store our preferences.
GSettings requires a schema that describes our settings:</para>
<informalexample>
<programlisting><xi:include href="@abs_top_srcdir@/examples/application5/org.gtk.exampleapp.gschema.xml" parse="text"><xi:fallback>MISSING XINCLUDE CONTENT</xi:fallback></xi:include></programlisting>
</informalexample>
<para>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 <ulink url="https://developer.gnome.org/gio/2.36/ch31s06.html">macros</ulink>
to do this in autotools-based projects.</para>
<para>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.</para>
<informalexample>
<programlisting><![CDATA[
...
static void
example_app_window_init (ExampleAppWindow *win)
{
ExampleAppWindowPrivate *priv;
priv = example_app_window_get_instance_private (win);
gtk_widget_init_template (GTK_WIDGET (win));
priv->settings = g_settings_new ("org.gtk.exampleapp");
g_settings_bind (priv->settings, "transition",
priv->stack, "transition-type",
G_SETTINGS_BIND_DEFAULT);
}
...
]]></programlisting>
<para>(<ulink url="https://gitlab.gnome.org/GNOME/gtk/blob/gtk-3-22/examples/application5/exampleappwin.c">full source</ulink>)</para>
</informalexample>
<para>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.</para>
<para>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.</para>
<para>Lets start with the template.</para>
<informalexample>
<programlisting><xi:include href="@abs_top_srcdir@/examples/application6/prefs.ui" parse="text"><xi:fallback>MISSING XINCLUDE CONTENT</xi:fallback></xi:include></programlisting>
</informalexample>
<para>Next comes the dialog subclass.</para>
<informalexample>
<programlisting><xi:include href="@abs_top_srcdir@/examples/application6/exampleappprefs.c" parse="text"><xi:fallback>MISSING XINCLUDE CONTENT</xi:fallback></xi:include></programlisting>
</informalexample>
<para>Now we revisit the <literal>preferences_activated(<!-- -->)</literal> function in our
application class, and make it open a new preference dialog.</para>
<informalexample>
<programlisting><![CDATA[
...
static void
preferences_activated (GSimpleAction *action,
GVariant *parameter,
gpointer app)
{
ExampleAppPrefs *prefs;
GtkWindow *win;
win = gtk_application_get_active_window (GTK_APPLICATION (app));
prefs = example_app_prefs_new (EXAMPLE_APP_WINDOW (win));
gtk_window_present (GTK_WINDOW (prefs));
}
...
]]></programlisting>
<para>(<ulink url="https://gitlab.gnome.org/GNOME/gtk/blob/gtk-3-22/examples/application6/exampleapp.c">full source</ulink>)</para>
</informalexample>
<para>After all this work, our application can now show
a preference dialog like this:</para>
<informalfigure>
<mediaobject>
<imageobject>
<imagedata fileref="getting-started-app6.png" format="PNG"/>
</imageobject>
</mediaobject>
</informalfigure>
</section>
<section>
<title>Adding a search bar</title>
<para>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.</para>
<para>We add a toggle button to the header bar, which can be used
to slide out the search bar below the header bar.</para>
<informalexample>
<programlisting><xi:include href="@abs_top_srcdir@/examples/application7/window.ui" parse="text"><xi:fallback>MISSING XINCLUDE CONTENT</xi:fallback></xi:include></programlisting>
</informalexample>
<para>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.</para>
<informalexample>
<programlisting><![CDATA[
...
static void
search_text_changed (GtkEntry *entry,
ExampleAppWindow *win)
{
ExampleAppWindowPrivate *priv;
const gchar *text;
GtkWidget *tab;
GtkWidget *view;
GtkTextBuffer *buffer;
GtkTextIter start, match_start, match_end;
text = gtk_entry_get_text (entry);
if (text[0] == '\0')
return;
priv = example_app_window_get_instance_private (win);
tab = gtk_stack_get_visible_child (GTK_STACK (priv->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);
...
}
...
]]></programlisting>
<para>(<ulink url="https://gitlab.gnome.org/GNOME/gtk/blob/gtk-3-22/examples/application7/exampleappwin.c">full source</ulink>)</para>
</informalexample>
<para>With the search bar, our application now looks like this:</para>
<informalfigure>
<mediaobject>
<imageobject>
<imagedata fileref="getting-started-app7.png" format="PNG"/>
</imageobject>
</mediaobject>
</informalfigure>
</section>
<section>
<title>Adding a side bar</title>
<para>As another piece of functionality, we are adding a sidebar,
which demonstrates #GtkMenuButton, #GtkRevealer and #GtkListBox.</para>
<informalexample>
<programlisting><xi:include href="@abs_top_srcdir@/examples/application8/window.ui" parse="text"><xi:fallback>MISSING XINCLUDE CONTENT</xi:fallback></xi:include></programlisting>
</informalexample>
<para>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.</para>
<para>As expected by now, the gears menu is specified in a GtkBuilder
ui file.</para>
<informalexample>
<programlisting><xi:include href="@abs_top_srcdir@/examples/application8/gears-menu.ui" parse="text"><xi:fallback>MISSING XINCLUDE CONTENT</xi:fallback></xi:include></programlisting>
</informalexample>
<para>To connect the menuitem to the show-words setting, we use
a #GAction corresponding to the given #GSettings key.</para>
<informalexample>
<programlisting><![CDATA[
...
static void
example_app_window_init (ExampleAppWindow *win)
{
...
builder = gtk_builder_new_from_resource ("/org/gtk/exampleapp/gears-menu.ui");
menu = G_MENU_MODEL (gtk_builder_get_object (builder, "menu"));
gtk_menu_button_set_menu_model (GTK_MENU_BUTTON (priv->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);
}
...
]]></programlisting>
<para>(<ulink url="https://gitlab.gnome.org/GNOME/gtk/blob/gtk-3-22/examples/application8/exampleappwin.c">full source</ulink>)</para>
</informalexample>
<para>What our application looks like now:</para>
<informalfigure>
<mediaobject>
<imageobject>
<imagedata fileref="getting-started-app8.png" format="PNG"/>
</imageobject>
</mediaobject>
</informalfigure>
</section>
<section>
<title>Properties</title>
<para>Widgets and other objects have many useful properties.</para>
<para>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.</para>
<para>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.</para>
<para>We add a new "Lines" menu item to the gears menu, which
triggers the show-lines action:</para>
<informalexample>
<programlisting><xi:include href="@abs_top_srcdir@/examples/application9/gears-menu.ui" parse="text"><xi:fallback>MISSING XINCLUDE CONTENT</xi:fallback></xi:include></programlisting>
</informalexample>
<para>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.</para>
<para>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.</para>
<informalexample>
<programlisting>
...
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);
}
...
</programlisting>
<para>(<ulink url="https://gitlab.gnome.org/GNOME/gtk/blob/gtk-3-22/examples/application9/exampleappwin.c">full source</ulink>)</para>
</informalexample>
<para>We also need a function that counts the lines of the currently
active tab, and updates the @lines label. See the
<ulink url="https://gitlab.gnome.org/GNOME/gtk/blob/gtk-3-22/examples/application9/exampleappwin.c">full source</ulink>
if you are interested in the details.</para>
<para>This brings our example application to this appearance:</para>
<informalfigure>
<mediaobject>
<imageobject>
<imagedata fileref="getting-started-app9.png" format="PNG"/>
</imageobject>
</mediaobject>
</informalfigure>
</section>
<section>
<title>Header bar</title>
<para>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.</para>
<informalexample>
<programlisting><xi:include href="@abs_top_srcdir@/examples/application10/window.ui" parse="text"><xi:fallback>MISSING XINCLUDE CONTENT</xi:fallback></xi:include></programlisting>
</informalexample>
<para>A small extra bonus of using a header bar is that we get
a fallback application menu for free. Here is how the
application now looks, if this fallback is used.</para>
<informalfigure>
<mediaobject>
<imageobject>
<imagedata fileref="getting-started-app10.png" format="PNG"/>
</imageobject>
</mediaobject>
</informalfigure>
<para>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.</para>
</section>
</section>
<section>
<title>Custom Drawing</title>
<para>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.
</para>
<para>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 the 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.</para>
<para>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.</para>
<informalfigure>
<mediaobject>
<imageobject>
<imagedata fileref="drawing.png" format="PNG"/>
</imageobject>
</mediaobject>
</informalfigure>
<example id="gtk-getting-started-drawing">
<title>Drawing in response to input</title>
<para>Create a new file with the following content named example-4.c.</para>
<programlisting><xi:include href="@abs_top_srcdir@/examples/drawing.c" parse="text"><xi:fallback>MISSING XINCLUDE CONTENT</xi:fallback></xi:include></programlisting>
</example>
<para>
You can compile the program above with GCC using:
<literallayout>
<literal>gcc `pkg-config --cflags gtk+-3.0` -o example-4 example-4.c `pkg-config --libs gtk+-3.0`</literal>
</literallayout>
</para>
</section>
</chapter>