Using c++-gtk-utils with GtkBuilder

The Cgu::WinBase and Cgu::MainWidgetBase classes can manage GTK+ objects constructed with GtkBuilder, and thus with UI interfaces generated by, say, glade, just as they can be used with GTK+ objects generated by hand. Lifetime management will work automatically (the Cgu::MainWidgetBase constructor calls g_object_ref_sink() to take ownership from the GtkBuilder object, and the Cgu::WinBase destructor calls gtk_widget_destroy() to correctly handle the reference count of top level windows).

With Cgu::WinBase, two different approaches are possible. First, the WinBase object can take an object comprising or derived from GtkWindow which has been generated by GtkBuilder in the ordinary way. Alternatively, Cgu::WinBase can construct its own GtkWindow object, and a widget heirarchy generated by GtkBuilder can be added to that top level window. The following two examples construct the demonstration Message class (as appearing in the Cgu::WinBase documentation) using GtkBuilder adopting either approach.

First, an example which attaches a widget heirarchy constructed with GtkBuilder to a GtkApplicationWindow object constructed with a Cgu::WinBase object:

#include <exception>
#include <string>
#include <gtk/gtk.h>
#include <c++-gtk-utils/window.h>
#include <c++-gtk-utils/shared_handle.h>
#include <c++-gtk-utils/gobj_handle.h>
#include <c++-gtk-utils/application.h>
#include <c++-gtk-utils/callback.h>
 
// *** class headers ***
 
class UiBuildError: public std::exception {
  Cgu::GcharSharedHandle message;
public:
  virtual const char* what() const throw() {return message.get();}
  UiBuildError(const char* msg):
    message(g_strdup_printf("UiBuildError: %s", msg)) {}
  ~UiBuildError() throw() {}
};
 
extern "C" void message_button_clicked(GtkWidget*, void*);
 
class Message: public Cgu::WinBase {
public:
  friend void message_button_clicked(GtkWidget*, void*);
  Message(const char* text, GApplication* app);
};
 
// *** class implementation ***
 
// *** Message menu actions ***
 
namespace {
extern "C" {
 
void app_beep(GSimpleAction*,
              GVariant*,
              void*) {
  gdk_beep();
}
 
void app_quit(GSimpleAction*,
              GVariant*,
              void* data) {
  Cgu::Application* app = static_cast<Cgu::Application*>(data);
  std::list<Cgu::WinBase*> wins = app->get_windows();
  for (auto iter = wins.begin(); iter != wins.end(); ++iter) {
    delete *iter;  // this will also remove the Message object from
                   // the Cgu::Application object
  }
}
 
GActionEntry app_entries[] = {
  { "beep", app_beep, NULL, NULL, NULL },
  { "quit", app_quit, NULL, NULL, NULL },
};
 
void win_beep(GSimpleAction*, GVariant*, void*) {
  gdk_beep();
}
 
GActionEntry win_entries[] = {
  { "beep", win_beep, NULL, NULL, NULL },
};
 
} // extern "C"
} // unnamed namespace           
 
// *** Message callbacks ***
                        
void message_button_clicked(GtkWidget*, void* data) {
  static_cast<Message*>(data)->close();
}
 
// *** Message UI and menu XML definitions
 
const gchar ui[] =
"<interface>"
"  <object class='GtkVBox' id='vbox'>"
"    <property name='homogeneous'>FALSE</property>"
"    <property name='spacing'>2</property>"
"    <child>"
"      <object class='GtkLabel' id='label'>"
"      </object>"
"      <packing>"
"        <property name='fill'>FALSE</property>"
"      </packing>"
"    </child>"
"    <child>"
"      <object class='GtkHButtonBox' id='bbox'>"
"        <child>"
"          <object class='GtkButton' id='button'>"
"            <property name='label'>gtk-ok</property>"
"            <property name='use-stock'>TRUE</property>"
"            <property name='can-focus'>TRUE</property>"
"          </object>"
"        </child>"
"      </object>"
"      <packing>"
"        <property name='expand'>FALSE</property>"
"        <property name='fill'>FALSE</property>"
"      </packing>"
"    </child>"
"  </object>"
"</interface>";
 
const gchar menus[] =
"<interface>"
"  <menu id='app-menu'>"
"    <section>"
"      <item>"
"        <attribute name='label'>Beep</attribute>"
"        <attribute name='action'>app.beep</attribute>"
"      </item>"
"      <item>"
"        <attribute name='label'>_Quit</attribute>"
"        <attribute name='action'>app.quit</attribute>"
"      </item>"
"    </section>"
"  </menu>"
"  <menu id='menubar'>"
"    <submenu>"
"      <attribute name='label'>Menu1</attribute>"
"      <section>"
"        <item>"
"          <attribute name='label'>More beep</attribute>"
"          <attribute name='action'>win.beep</attribute>"
"        </item>"
"      </section>"
"    </submenu>"
"  </menu>"
"</interface>";
 
// *** Message methods
 
Message::Message(const char* text,
                 GApplication* app):
    Cgu::WinBase{"Message", 0,
                 false, 0,
                 GTK_WINDOW(gtk_application_window_new(GTK_APPLICATION(app)))} {
 
  g_action_map_add_action_entries(G_ACTION_MAP(get_win()),
                                  win_entries,
                                  G_N_ELEMENTS(win_entries),
                                  static_cast<void*>(0));
 
  Cgu::GobjHandle<GtkBuilder> builder{gtk_builder_new()};
  GError* err = 0;
  if (!gtk_builder_add_from_string(builder, ui, sizeof(ui) - 1, &err)) {
    std::string msg{"Message::build_interface: "};
    msg += err->message;
    throw UiBuildError{msg.c_str()};
  }
 
  GObject* component = gtk_builder_get_object(builder, "vbox");
  if (!component) {
    throw UiBuildError{"Message constructor: Can't find 'vbox' object"};
  }
  gtk_container_add(GTK_CONTAINER(get_win()), GTK_WIDGET(component));
 
  component = gtk_builder_get_object(builder, "label");
  if (!component) {
    throw UiBuildError{"Message constructor: Can't find 'label' object"};
  }
  gtk_label_set_text(GTK_LABEL(component), text);
 
  component = gtk_builder_get_object(builder, "button");
  if (!component) {
    throw UiBuildError{"Message constructor: Can't find 'button' object"};
  }
  g_signal_connect(component, "clicked",
                   G_CALLBACK(message_button_clicked), this);
 
  gtk_widget_show_all(GTK_WIDGET(get_win()));
}
 
// *** Cgu::Application callbacks
 
void startup(Cgu::Application* app) {
  g_action_map_add_action_entries(G_ACTION_MAP(app->get_g_app()),
                                  app_entries,
                                  G_N_ELEMENTS(app_entries),
                                  app);
 
  // we cannot propagate exceptions out of the signal handler, so use
  // gtk_builder_new_from_string() and error out if loading fails
  Cgu::GobjHandle<GtkBuilder> builder{gtk_builder_new_from_string(menus, -1)};
 
  GObject* component = gtk_builder_get_object(builder, "app-menu");
  if (!component) {
    g_error("%s", "startup: Can't find 'app-menu' object");
  }
  gtk_application_set_app_menu(GTK_APPLICATION(app->get_g_app()),
                               G_MENU_MODEL(component)); 
 
  component = gtk_builder_get_object(builder, "menubar");
  if (!component) {
    g_error("%s", "startup: Can't find 'menubar' object");
  }
  gtk_application_set_menubar(GTK_APPLICATION(app->get_g_app()),
                              G_MENU_MODEL(component));
}
 
void activate(Cgu::Application* app) {
  if (app->get_win_count() > 0) {
    gtk_window_present(app->get_windows().front()->get_win());
    return;
  }
 
  // we cannot propagate exceptions out of the signal handler, so
  // error out with g_error if there is an exception
  Cgu::WinBase* dialog;
  try {
    dialog = new Message{"This is a message", app->get_g_app()};
  }
  catch (std::exception& e) {
    g_error("%s", e.what());    
  }
  dialog->show_all();
 
  app->add(dialog);
}
 
// *** user code ***
 
int main(int argc, char* argv[]) {
  Cgu::Application app{"my_prog", G_APPLICATION_FLAGS_NONE};
  app.startup.connect(Cgu::Callback::make(startup));
  app.activate.connect(Cgu::Callback::make(activate));
  return app.run(0, 0);
}

Secondly, an example which constructs the top level window and all its children using GtkBuilder:

#include <exception>
#include <string>
#include <gtk/gtk.h>
#include <c++-gtk-utils/window.h>
#include <c++-gtk-utils/shared_handle.h>
#include <c++-gtk-utils/gobj_handle.h>
#include <c++-gtk-utils/application.h>
#include <c++-gtk-utils/callback.h>
 
// *** class headers ***
 
class UiBuildError: public std::exception {
  Cgu::GcharSharedHandle message;
public:
  virtual const char* what() const throw() {return message.get();}
  UiBuildError(const char* msg):
    message(g_strdup_printf("UiBuildError: %s", msg)) {}
  ~UiBuildError() throw() {}
};
 
extern "C" void message_button_clicked(GtkWidget*, void*);
 
// Message objects are constructed from GtkBuilder objects. The class
// has two helper static member functions, get_window() and
// build_interface().
class Message: public Cgu::WinBase {
  // get_window() must be static as it is called when initialising the
  // base class
  static GtkWindow* get_window(const Cgu::GobjHandle<GtkBuilder>&);
public:
  // build_interface() must be static as it is invoked before the
  // Message object constructor is entered
  static Cgu::GobjHandle<GtkBuilder> build_interface();
 
  friend void message_button_clicked(GtkWidget*, void*);
 
  // the Message::build_interface() static member function provides
  // the in-built default UI for Message objects.  Alternative
  // interfaces can be passed when the Message object is constructed,
  // but they must provide the 'win', 'label' and 'button' objects or
  // the constructor will throw UiBuildError
  Message(const char* text,
          GApplication* app,
          const Cgu::GobjHandle<GtkBuilder>& = Message::build_interface());
};
 
// *** class implementation ***
 
// *** Message menu actions ***
 
namespace {
extern "C" {
 
void app_beep(GSimpleAction*,
              GVariant*,
              void*) {
  gdk_beep();
}
 
void app_quit(GSimpleAction*,
              GVariant*,
              void* data) {
  Cgu::Application* app = static_cast<Cgu::Application*>(data);
  std::list<Cgu::WinBase*> wins = app->get_windows();
  for (auto iter = wins.begin(); iter != wins.end(); ++iter) {
    delete *iter;  // this will also remove the Message object from
                   // the Cgu::Application object
  }
}
 
GActionEntry app_entries[] = {
  { "beep", app_beep, NULL, NULL, NULL },
  { "quit", app_quit, NULL, NULL, NULL },
};
 
void win_beep(GSimpleAction*, GVariant*, void*) {
  gdk_beep();
}
 
GActionEntry win_entries[] = {
  { "beep", win_beep, NULL, NULL, NULL },
};
 
} // extern "C"
} // unnamed namespace           
 
// *** Message callbacks ***
                             
void message_button_clicked(GtkWidget*, void* data) {
  static_cast<Message*>(data)->close();
}
 
// *** Message UI and menu XML definitions
 
// this is the default UI for Message objects, obtained by calling
// Message::build_interface().  Any custom interface passed to the
// Message constructor must provide 'win', 'label' and 'button'
// objects.  The remainder are optional.  A custom interface could
// for example provide an icon in the window, or change layout.
const gchar ui[] =
"<interface>"
"  <object class='GtkApplicationWindow' id='win'>"
"    <child>"
"      <object class='GtkVBox' id='vbox'>"
"        <property name='homogeneous'>FALSE</property>"
"        <property name='spacing'>2</property>"
"        <child>"
"          <object class='GtkLabel' id='label'>"
"          </object>"
"          <packing>"
"            <property name='fill'>FALSE</property>"
"          </packing>"
"        </child>"
"        <child>"
"          <object class='GtkHButtonBox' id='bbox'>"
"            <child>"
"              <object class='GtkButton' id='button'>"
"                <property name='label'>gtk-ok</property>"
"                <property name='use-stock'>TRUE</property>"
"                <property name='can-focus'>TRUE</property>"
"              </object>"
"            </child>"
"          </object>"
"          <packing>"
"            <property name='expand'>FALSE</property>"
"            <property name='fill'>FALSE</property>"
"          </packing>"
"        </child>"
"      </object>"
"    </child>"
"  </object>"
"</interface>";
 
const gchar menus[] =
"<interface>"
"  <menu id='app-menu'>"
"    <section>"
"      <item>"
"        <attribute name='label'>Beep</attribute>"
"        <attribute name='action'>app.beep</attribute>"
"      </item>"
"      <item>"
"        <attribute name='label'>_Quit</attribute>"
"        <attribute name='action'>app.quit</attribute>"
"      </item>"
"    </section>"
"  </menu>"
"  <menu id='menubar'>"
"    <submenu>"
"      <attribute name='label'>Menu1</attribute>"
"      <section>"
"        <item>"
"          <attribute name='label'>More beep</attribute>"
"          <attribute name='action'>win.beep</attribute>"
"        </item>"
"      </section>"
"    </submenu>"
"  </menu>"
"</interface>";
 
// *** Message methods
 
GtkWindow* Message::get_window(const Cgu::GobjHandle<GtkBuilder>& builder) {
  GObject* win = gtk_builder_get_object(builder, "win");
  if (!win) {
    throw UiBuildError{"Message::get_window(): Can't find 'win' object"};
  }
  return GTK_WINDOW(win);
}
 
Cgu::GobjHandle<GtkBuilder> Message::build_interface() {
  Cgu::GobjHandle<GtkBuilder> builder{gtk_builder_new()};
  GError* err = 0;
  if (!gtk_builder_add_from_string(builder, ui, sizeof(ui) - 1, &err)) {
    std::string msg{"Message::build_interface: "};
    msg += err->message;
    throw UiBuildError{msg.c_str()};
  }
  return builder;
}
 
Message::Message(const char* text,
                 GApplication* app,
                 const Cgu::GobjHandle<GtkBuilder>& builder): Cgu::WinBase{"Message", 0,
                                                                           false, 0,
                                                                           get_window(builder)} {
 
  // set the application property of the GtkApplicationWindow object
  // to the underlying GtkApplication object before we add action
  // entries - GtkBuilder cannot do this for us and sets the
  // application property to NULL
  g_object_set(get_win(),
              "application", app,
              static_cast<void*>(0));
 
  g_action_map_add_action_entries(G_ACTION_MAP(get_win()),
                                  win_entries,
                                  G_N_ELEMENTS(win_entries),
                                  static_cast<void*>(0));
 
  GObject* component = gtk_builder_get_object(builder, "label");
  if (!component) {
    throw UiBuildError{"Message constructor: Can't find 'label' object"};
  }
  gtk_label_set_text(GTK_LABEL(component), text);
 
  component = gtk_builder_get_object(builder, "button");
  if (!component) {
    throw UiBuildError{"Message constructor: Can't find 'button' object"};
  }
  g_signal_connect(component, "clicked",
                   G_CALLBACK(message_button_clicked), this);
 
  gtk_widget_show_all(GTK_WIDGET(get_win()));
}
 
// *** Cgu::Application callbacks
 
void startup(Cgu::Application* app) {
  g_action_map_add_action_entries(G_ACTION_MAP(app->get_g_app()),
                                  app_entries,
                                  G_N_ELEMENTS(app_entries),
                                  app);
 
  // we cannot propagate exceptions out of the signal handler, so use
  // gtk_builder_new_from_string() and error out if loading fails
  Cgu::GobjHandle<GtkBuilder> builder{gtk_builder_new_from_string(menus, -1)};
 
  GObject* component = gtk_builder_get_object(builder, "app-menu");
  if (!component) {
    g_error("%s", "startup: Can't find 'app-menu' object");
  }
  gtk_application_set_app_menu(GTK_APPLICATION(app->get_g_app()),
                               G_MENU_MODEL(component)); 
 
  component = gtk_builder_get_object(builder, "menubar");
  if (!component) {
    g_error("%s", "startup: Can't find 'menubar' object");
  }
  gtk_application_set_menubar(GTK_APPLICATION(app->get_g_app()),
                              G_MENU_MODEL(component));
}
 
void activate(Cgu::Application* app) {
  if (app->get_win_count() > 0) {
    gtk_window_present(app->get_windows().front()->get_win());
    return;
  }
 
  // we cannot propagate exceptions out of the signal handler, so
  // error out with g_error if there is an exception
  Cgu::WinBase* dialog;
  try {
    dialog = new Message{"This is a message", app->get_g_app()};
  }
  catch (std::exception& e) {
    g_error("%s", e.what());    
  }
  dialog->show_all();
 
  app->add(dialog);
}
 
// *** user code ***
 
int main(int argc, char* argv[]) {
  Cgu::Application app{"my_prog", G_APPLICATION_FLAGS_NONE};
  app.startup.connect(Cgu::Callback::make(startup));
  app.activate.connect(Cgu::Callback::make(activate));
  return app.run(0, 0);
}

Care must be taken if initializing a Cgu::GobjHandle object with a widget or GObject object obtained from GtkBuilder. It is necessary to call g_object_ref() by hand in that case, as the Cgu::GobjHandle constructor taking a pointer does not call g_object_ref_sink() if the initializing object does not have a floating reference, and GtkBuilder always sinks floating references itself.