c++-gtk-utils: Using c++-gtk-utils with GtkBuilder

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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 constructs the top level window and all its children using GtkBuilder:

#include <exception>
#include <gtk/gtk.h>
#include <c++-gtk-utils/window.h>
#include <c++-gtk-utils/shared_handle.h>
#include <c++-gtk-utils/gobj_handle.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 memberer 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, const Cgu::GobjHandle<GtkBuilder>& = Message::build_interface());
};
// *** class implementation ***
void message_button_clicked(GtkWidget*, void* data) {
static_cast<Message*>(data)->close();
}
// 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='GtkWindow' 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>";
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());
if (!gtk_builder_add_from_string(builder, ui, sizeof(ui) - 1, 0)) {
throw UiBuildError("Message::build_interface: Can't create interface from ui");
}
return builder;
}
Message::Message(const char* text,
const Cgu::GobjHandle<GtkBuilder>& builder): Cgu::WinBase("Message", 0,
true, 0,
get_window(builder)) {
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()));
}
// *** user code ***
int main(int argc, char* argv[]) {
gtk_init(&argc, &argv);
Message dialog("This is a message");
dialog.exec();
return 0;
}

Secondly, an example which attaches a widget heirarchy constructed with GtkBuilder to a GtkWindow object generated by the Cgu::WinBase object:

#include <exception>
#include <gtk/gtk.h>
#include <c++-gtk-utils/window.h>
#include <c++-gtk-utils/shared_handle.h>
#include <c++-gtk-utils/gobj_handle.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);
};
// *** class implementation ***
void message_button_clicked(GtkWidget*, void* data) {
static_cast<Message*>(data)->close();
}
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>";
Message::Message(const char* text): Cgu::WinBase("Message", 0, true) {
Cgu::GobjHandle<GtkBuilder> builder(gtk_builder_new());
if (!gtk_builder_add_from_string(builder, ui, sizeof(ui) - 1, 0)) {
throw UiBuildError("Message::build_interface: Can't create interface from ui");
}
GObject* component = gtk_builder_get_object(builder, "vbox");
gtk_container_add(GTK_CONTAINER(get_win()), GTK_WIDGET(component));
component = gtk_builder_get_object(builder, "label");
gtk_label_set_text(GTK_LABEL(component), text);
component = gtk_builder_get_object(builder, "button");
g_signal_connect(component, "clicked",
G_CALLBACK(message_button_clicked), this);
gtk_widget_show_all(GTK_WIDGET(get_win()));
}
// *** user code ***
int main(int argc, char* argv[]) {
gtk_init(&argc, &argv);
Message dialog("This is a message");
dialog.exec();
return 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.