GTK+ programs with GtkBuilder and dynamic signal handlers.

Well, I decided to review some GTK+ and Gnome development lately. With GTK+, a nice way to create a user interface is with the Glade Interface Designer. Glade produces an xml file with a glade-interface element that can be loaded by libglade. You can then change attributes of the user interface without having to recompile your program. You just edit the design xml file and you’re good to go. Here are a couple things I noted during the process that weren’t too clear from the documentation:

1. You have to work with C, not C++, if you want to dynamically load the signal handlers. Many times, it is convenient to write a program mostly in C, but use the C++ compiler and take advantage of a few of the niceties in C++. You can’t do that in this case. According to the libglade documentation, you’ll need to add -export-dynamic flag so that the dynamic loader for the signal handlers can locate the functions in the executable with the gmodule library. That doesn’t work with a C++ compiled executable. You’ll have to stick with C. If you really want to use GTK+ with C++, you can always try the glademm bindings instead of the default C bindings. You could also use gtkmm and write the entire program w/ C++ instead.

   UPDATE: I think you could get around this by using extern “C” around the function calls for the signal handlers. Then you could still use the automatic signal handlers while compiling with g++.

2. As of GTK+ 2.0, libglade is deprecated. There is a new GtkBuilder interface that does the same thing. You no longer need to compile and link against the libglade libraries. I searched all over for a new interface designer to replace Glade but found a lot of references to people still using Glade. The xml file produced by glade is not exactly the same and not compatible with the GtkBuilder interface however. I finally found that there is a conversion function included with GTK+ 2.0 that converts the glade file to a GtkBuilder xml file.

   gtk-builder-convert <input file> <output file>

Anyway, with those two items taken care of, here is a really simple program and a really simple Makefile I put together to show how to get a GTK+ 2.0 program window showing.

hello.c

#include 
void close_app(GtkWidget* widget,gpointer user_data) {
 gtk_main_quit();
}
int main (int argc, char **argv) {
 GtkBuilder *gtkBuilder;
 GtkWidget *mainwin;
 gtk_set_locale();
 /* Initialize the widget set */
 gtk_init (&argc, &argv);
 /* Create the main window */
 gtkBuilder= gtk_builder_new();
 gtk_builder_add_from_file(gtkBuilder,"hello.ui",NULL); 
 gtk_builder_connect_signals ( gtkBuilder, NULL );
 mainwin= GTK_WIDGET(gtk_builder_get_object(gtkBuilder,"window1"));
 g_object_unref ( G_OBJECT(gtkBuilder) );
 /* Show the application window */
 gtk_widget_show_all ( mainwin );
 /* Enter the main event loop, and wait for user interaction */
 gtk_main ();
 /* The user lost interest */
 return 0;
}

MakeFile
LIBS=$(shell pkg-config --cflags --libs gtk+-2.0)
CFLAGS=-Wall -g -export-dynamic
hello: hello.c hello.ui
    gcc -o hello hello.c $(LIBS) $(CFLAGS)
hello.ui: hello.glade
    gtk-builder-convert hello.glade hello.ui


hello.glade
For the sake of space, I’ll leave the xml contents out. Suffice it to say that there is a window, “window1”, and I set the destroy handler to “close_app”.

The Makefile converts hello.glade to hello.ui, which is loaded by the hello program at runtime to produce the UI. You can of course build a window dynamically at runtime and you can also choose to connect the signal handlers manually. It just struck me as a lot less C code to do it like this.