Dialog.useHeaderBar

true if the dialog uses a headerbar for action buttons instead of the action-area.

For technical reasons, this property is declared as an integer property, but you should only set it to true or false.

Creating a dialog with headerbar

Builtin gtk.dialog.Dialog subclasses such as gtk.color_chooser_dialog.ColorChooserDialog set this property according to platform conventions (using the property@Gtk.Settings:gtk-dialogs-use-header setting).

Here is how you can achieve the same:

g_object_get (settings, "gtk-dialogs-use-header", &header, NULL);
dialog = g_object_new (GTK_TYPE_DIALOG, header, TRUE, NULL);