gtk.expander.Expander allows the user to reveal its child by clicking on an expander triangle.

This is similar to the triangles used in a gtk.tree_view.TreeView.

Normally you use an expander as you would use a frame; you create the child widget and use gtk.expander.Expander.setChild to add it to the expander. When the expander is toggled, it will take care of showing and hiding the child automatically.

Special Usage

There are situations in which you may prefer to show and hide the expanded widget yourself, such as when you want to actually create the widget at expansion time. In this case, create a gtk.expander.Expander but do not add a child to it. The expander widget has an gtk.expander.Expander.gboolean property which can be used to monitor its expansion state. You should watch this property with a signal connection as follows:

static void
expander_callback (GObject    *object,
                   GParamSpec *param_spec,
                   gpointer    user_data)
{
  GtkExpander *expander;

  expander = GTK_EXPANDER (object);

  if (gtk_expander_get_expanded (expander))
    {
      // Show or create widgets
    }
  else
    {
      // Hide or destroy widgets
    }
}

static void
create_expander (void)
{
  GtkWidget *expander = gtk_expander_new_with_mnemonic ("_More Options");
  g_signal_connect (expander, "notify::expanded",
                    G_CALLBACK (expander_callback), NULL);

  // ...
}

GtkExpander as GtkBuildable

The gtk.expander.Expander implementation of the gtk.buildable.Buildable interface supports placing a child in the label position by specifying “label” as the “type” attribute of a <child> element. A normal content child can be specified without specifying a <child> type attribute.

An example of a UI definition fragment with GtkExpander:

<object class="GtkExpander">
  <child type="label">
    <object class="GtkLabel" id="expander-label"/>
  </child>
  <child>
    <object class="GtkEntry" id="expander-content"/>
  </child>
</object>

CSS nodes

expander-widget
╰── box
    ├── title
    │   ├── expander
    │   ╰── <label widget>
    ╰── <child>

gtk.expander.Expander has a main node expander-widget, and subnode box containing the title and child widget. The box subnode title contains node expander, i.e. the expand/collapse arrow; then the label widget if any. The arrow of an expander that is showing its child gets the :checked pseudoclass set on it.

Accessibility

gtk.expander.Expander uses the gtk.types.AccessibleRole.Button role.