gtk2/docs/reference/gtk/getting_started.xml

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<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
               "http://www.oasis-open.org/docbook/xml/4.3/docbookx.dtd" [
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<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="../../../../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="../../../../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="../../../../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="../../../../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="../../../../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="../../../../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="../../../../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="../../../../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="../../../../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="../../../../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://git.gnome.org/browse/gtk+/tree/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 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:
      </para>

      <informalexample>
        <programlisting><xi:include href="../../../../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://git.gnome.org/browse/gtk+/tree/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://git.gnome.org/browse/gtk+/tree/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="../../../../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] = { "&lt;Ctrl&gt;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://git.gnome.org/browse/gtk+/tree/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="../../../../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://git.gnome.org/browse/gtk+/tree/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="../../../../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="../../../../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://git.gnome.org/browse/gtk+/tree/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="../../../../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://git.gnome.org/browse/gtk+/tree/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="../../../../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="../../../../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://git.gnome.org/browse/gtk+/tree/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="../../../../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://git.gnome.org/browse/gtk+/tree/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://git.gnome.org/browse/gtk+/tree/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="../../../../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="../../../../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>