In this step, we use a Gtk::Builder instance to associate a Gtk::Builder ui file with our application window class.

Our simple ui file gives the window a title, and puts a Gtk::Stack widget as the main content.

To make use of this file in our application, we revisit our Gtk::ApplicationWindow subclass, and call Gtk::Builder::create_from_resource() and Gtk::Builder::get_widget_derived() from the ExampleAppWindow::create() method to get an instance of our subclassed Gtk::ApplicationWindow. See the Using derived widgets section for more information about get_widget_derived().

You may have noticed that we use the _from_resource() variant of the method that reads the ui file. 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. 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 --target=resources.c --generate-source exampleapp.gresource.xml

The Gio::Resource and glib-compile-resources section contains more information about resource files. If you build with Meson, use the compile_resources() function in Meson's GNOME module.

Our application now looks like this:

Source Code

File: exampleapplication.h (For use with gtkmm 4)

#include "../step1/exampleapplication.h"
// Equal to the corresponding file in step1

File: exampleappwindow.h (For use with gtkmm 4)

#ifndef GTKMM_EXAMPLEAPPWINDOW_H_
#define GTKMM_EXAMPLEAPPWINDOW_H_

#include <gtkmm.h>

class ExampleAppWindow : public Gtk::ApplicationWindow
{
public:
  ExampleAppWindow(BaseObjectType* cobject,
    const Glib::RefPtr<Gtk::Builder>& refBuilder);

  static ExampleAppWindow* create();

  void open_file_view(const Glib::RefPtr<Gio::File>& file);

protected:
  Glib::RefPtr<Gtk::Builder> m_refBuilder;
};

#endif /* GTKMM_EXAMPLEAPPWINDOW_H */

File: exampleapplication.cc (For use with gtkmm 4)

#include "exampleapplication.h"
#include "exampleappwindow.h"
#include <iostream>
#include <exception>

ExampleApplication::ExampleApplication()
: Gtk::Application("org.gtkmm.examples.application", Gio::Application::Flags::HANDLES_OPEN)
{
}

Glib::RefPtr<ExampleApplication> ExampleApplication::create()
{
  return Glib::make_refptr_for_instance<ExampleApplication>(new ExampleApplication());
}

ExampleAppWindow* ExampleApplication::create_appwindow()
{
  auto appwindow = ExampleAppWindow::create();

  // Make sure that the application runs for as long this window is still open.
  add_window(*appwindow);

  // A window can be added to an application with Gtk::Application::add_window()
  // or Gtk::Window::set_application(). When all added windows have been hidden
  // or removed, the application stops running (Gtk::Application::run() returns()),
  // unless Gio::Application::hold() has been called.

  // Delete the window when it is hidden.
  appwindow->signal_hide().connect([appwindow](){ delete appwindow; });

  return appwindow;
}

void ExampleApplication::on_activate()
{
  try
  {
    // The application has been started, so let's show a window.
    auto appwindow = create_appwindow();
    appwindow->present();
  }
  // If create_appwindow() throws an exception (perhaps from Gtk::Builder),
  // no window has been created, no window has been added to the application,
  // and therefore the application will stop running.
  catch (const Glib::Error& ex)
  {
    std::cerr << "ExampleApplication::on_activate(): " << ex.what() << std::endl;
  }
  catch (const std::exception& ex)
  {
    std::cerr << "ExampleApplication::on_activate(): " << ex.what() << std::endl;
  }
}

void ExampleApplication::on_open(const Gio::Application::type_vec_files& files,
  const Glib::ustring& /* hint */)
{
  // The application has been asked to open some files,
  // so let's open a new view for each one.
  ExampleAppWindow* appwindow = nullptr;
  auto windows = get_windows();
  if (windows.size() > 0)
    appwindow = dynamic_cast<ExampleAppWindow*>(windows[0]);

  try
  {
    if (!appwindow)
      appwindow = create_appwindow();

    for (const auto& file : files)
      appwindow->open_file_view(file);

    appwindow->present();
  }
  catch (const Glib::Error& ex)
  {
    std::cerr << "ExampleApplication::on_open(): " << ex.what() << std::endl;
  }
  catch (const std::exception& ex)
  {
    std::cerr << "ExampleApplication::on_open(): " << ex.what() << std::endl;
  }
}

File: exampleappwindow.cc (For use with gtkmm 4)

#include "exampleappwindow.h"
#include <stdexcept>

ExampleAppWindow::ExampleAppWindow(BaseObjectType* cobject,
  const Glib::RefPtr<Gtk::Builder>& refBuilder)
: Gtk::ApplicationWindow(cobject),
  m_refBuilder(refBuilder)
{
}

//static
ExampleAppWindow* ExampleAppWindow::create()
{
  // Load the Builder file and instantiate its widgets.
  auto refBuilder = Gtk::Builder::create_from_resource("/org/gtkmm/exampleapp/window.ui");

  auto window = Gtk::Builder::get_widget_derived<ExampleAppWindow>(refBuilder, "app_window");
  if (!window)
    throw std::runtime_error("No \"app_window\" object in window.ui");

  return window;
}

void ExampleAppWindow::open_file_view(const Glib::RefPtr<Gio::File>& /* file */)
{
}

File: main.cc (For use with gtkmm 4)

#include "../step1/main.cc"
// Equal to the corresponding file in step1

File: exampleapp.gresource.xml (For use with gtkmm 4)

<?xml version="1.0" encoding="UTF-8"?>
<gresources>
  <gresource prefix="/org/gtkmm/exampleapp">
    <file preprocess="xml-stripblanks">window.ui</file>
  </gresource>
</gresources>

File: window.ui (For use with gtkmm 4)

<?xml version="1.0" encoding="UTF-8"?>
<interface>
  <object class="GtkApplicationWindow" id="app_window">
    <property name="title" translatable="yes">Example Application</property>
    <property name="default-width">600</property>
    <property name="default-height">400</property>
    <property name="hide-on-close">True</property>
    <child>
      <object class="GtkBox" id="content_box">
        <property name="orientation">vertical</property>
        <child>
          <object class="GtkStack" id="stack"/>
        </child>
      </object>
    </child>
  </object>
</interface>