Building user interfaces

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.

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.

Example 3. Packing buttons with GtkBuilder Create a new file with the following content named example-3.c. #include <gtk/gtk.h> static void print_hello (GtkWidget *widget, gpointer data) { g_print ("Hello World

"); } int main (int argc, char *argv[]) { GtkBuilder *builder; GObject *window; GObject *button; GError *error = NULL; gtk_init (&argc, &argv); /* Construct a GtkBuilder instance and load our UI description */ builder = gtk_builder_new (); if (gtk_builder_add_from_file (builder, "builder.ui", &error) == 0) { g_printerr ("Error loading file: %s

", error->message); g_clear_error (&error); return 1; } /* Connect signal handlers to the constructed widgets. */ window = gtk_builder_get_object (builder, "window"); g_signal_connect (window, "destroy", G_CALLBACK (gtk_main_quit), NULL); button = gtk_builder_get_object (builder, "button1"); g_signal_connect (button, "clicked", G_CALLBACK (print_hello), NULL); button = gtk_builder_get_object (builder, "button2"); g_signal_connect (button, "clicked", G_CALLBACK (print_hello), NULL); button = gtk_builder_get_object (builder, "quit"); g_signal_connect (button, "clicked", G_CALLBACK (gtk_main_quit), NULL); gtk_main (); return 0; } Create a new file with the following content named builder.ui. <interface> <object id="window" class="GtkWindow"> <property name="visible">True</property> <property name="title">Grid</property> <property name="border-width">10</property> <child> <object id="grid" class="GtkGrid"> <property name="visible">True</property> <child> <object id="button1" class="GtkButton"> <property name="visible">True</property> <property name="label">Button 1</property> </object> <packing> <property name="left-attach">0</property> <property name="top-attach">0</property> </packing> </child> <child> <object id="button2" class="GtkButton"> <property name="visible">True</property> <property name="label">Button 2</property> </object> <packing> <property name="left-attach">1</property> <property name="top-attach">0</property> </packing> </child> <child> <object id="quit" class="GtkButton"> <property name="visible">True</property> <property name="label">Quit</property> </object> <packing> <property name="left-attach">0</property> <property name="top-attach">1</property> <property name="width">2</property> </packing> </child> </object> <packing> </packing> </child> </object> </interface>

You can compile the program above with GCC using:



gcc `pkg-config --cflags gtk+-3.0` -o example-3 example-3.c `pkg-config --libs gtk+-3.0`



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*.

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 /usr/share/ appname .