How to subclass GTK IconView in Vala with Glade - oop

Question

When I try to subclass a GTK IconView in Vala using Glade, I get a segmentation fault. Is this a bug in Vala, or am I just doing something wrong? This is using vala 0.42.3. Maybe this is related to how IconView doesn't have a base() constructor? (see: Chain up to 'Gtk.Box.new' not supported)
test.vala:
using Gtk;
public class IconViewSubclass : Gtk.IconView {
public IconViewSubclass() {
}
}
public static int main(string[] args) {
Gtk.init(ref args);
var builder = new Builder.from_file("test.glade");
var window = builder.get_object("window") as Window;
var iconViewSubclass = builder.get_object("iconViewSubclass") as IconViewSubclass;
iconViewSubclass.set_pixbuf_column(0);
iconViewSubclass.set_text_column(1);
window.show_all();
Gtk.main();
return 0;
}
test.glade:
<?xml version="1.0" encoding="UTF-8"?>
<!-- Generated with glade 3.22.1 -->
<interface>
<requires lib="gtk+" version="3.20"/>
<object class="GtkListStore" id="store">
<columns>
<!-- column-name pixbuf -->
<column type="GdkPixbuf"/>
<!-- column-name text -->
<column type="gchararray"/>
</columns>
</object>
<object class="GtkWindow" id="window">
<property name="can_focus">False</property>
<child>
<placeholder/>
</child>
<child>
<object class="GtkIconView" id="iconViewSubclass">
<property name="visible">True</property>
<property name="can_focus">True</property>
<property name="margin">6</property>
<property name="model">store</property>
</object>
</child>
</object>
</interface>
$ valac --pkg gtk+-3.0 test.vala && ./test
Segmentation fault

Answer 1

It looks like you need to let the Gtk.Builder know IconViewSubclass exists using expose_object(). This allows the sub-type to be used in the Builder UI definition file. Here's an example that compiles and does not segfault:
test.ui:
<?xml version="1.0" encoding="UTF-8"?>
<!-- Generated with glade 3.22.1 -->
<interface>
<requires lib="gtk+" version="3.18"/>
<object class="GtkWindow" id="window">
<property name="window-position">GTK_WIN_POS_CENTER</property>
<property name="default-height">250</property>
<property name="default-width">250</property>
<child>
<placeholder/>
</child>
<child>
<object class="IconViewSubclass" id="iconViewSubclass">
<property name="visible">True</property>
<property name="can_focus">True</property>
<property name="margin">6</property>
</object>
</child>
</object>
</interface>
and test.vala:
using Gtk;
public class IconViewSubclass : Gtk.IconView {}
public static int main(string[] args) {
Gtk.init(ref args);
var builder = new Builder ();
builder.expose_object ("IconViewSubclass", new IconViewSubclass ());
try {
builder.add_from_file ("test.ui");
} catch (Error error) {
print (#"$(error.message)");
}
var window = builder.get_object ("window") as Window;
var iconViewSubclass = (IconViewSubclass)builder.get_object ("iconViewSubclass");
iconViewSubclass.set_pixbuf_column (0);
iconViewSubclass.set_text_column (1);
window.show_all();
Gtk.main();
return 0;
}
You may want to look into using templates with Vala [GtkTemplate], [GtkChild] and [GtkCallback] attributes. The attributes will tell Vala to generate the boiler plate code for you.

Answer 2

AIThomas' code worked great, however, in order to continue editing the UI file in Glade I had to add a catalog file, as follows:
<?xml version="1.0" encoding="UTF-8"?>
<glade-catalog name="test" depends="gtk+">
<glade-widget-classes>
<glade-widget-class name="IconViewSubclass" generic-name="iconviewsubclass" title="IconViewSubclass" parent="GtkIconView"/>
</glade-widget-classes>
<glade-widget-group name="test" title="test">
<glade-widget-class-ref name="IconViewSubclass"/>
</glade-widget-group>
</glade-catalog>
I also discovered that the subclass name in Vala must correspond exactly with the widget name in the UI XML, i.e. changing IconViewSubclass to IconViewSubclass2 in test.vala will give you:
$ valac --pkg gtk+-3.0 test.vala && ./test
test.ui:14:1 Invalid object type 'IconViewSubclass'Segmentation fault
You can also use a namespace as part of the class name, i.e. namespace Foo { public class Bar : Baz } should work for a widget of type FooBar in the UI XML file.