expander: Check for an existing child when adding

Now that GtkExpander subclasses GtkContainer instead of GtkBin, it needs
its own guard against adding more than one child.

Also, the documentation should no longer describe adding a child as if
it is descended from GtkBin.

diff --git a/gtk/gtkexpander.c b/gtk/gtkexpander.c
index 4b7fb1490917f0abd6e4118151c3a3d292df33a0..1756682561975b6701a13966bbd294c1e79750c9 100644 (file)
--- a/gtk/gtkexpander.c
+++ b/gtk/gtkexpander.c
@@ -27,7 +27,7 @@
  * A #GtkExpander allows the user to hide or show its child by clicking
  * on an expander triangle similar to the triangles used in a #GtkTreeView.
  *
- * Normally you use an expander as you would use any other descendant
+ * Normally you use an expander as you would use a descendant
  * of #GtkBin; you create the child widget and use gtk_container_add()
  * to add it to the expander. When the expander is toggled, it will take
  * care of showing and hiding the child automatically.
@@ -786,6 +786,18 @@ gtk_expander_add (GtkContainer *container,
   GtkExpander *expander = GTK_EXPANDER (container);
   GtkExpanderPrivate *priv = gtk_expander_get_instance_private (expander);
 
+  if (priv->child != NULL)
+    {
+      g_warning ("Attempting to add a widget with type %s to a %s, "
+                 "but a %s can only contain one widget at a time; "
+                 "it already contains a widget of type %s",
+                 g_type_name (G_OBJECT_TYPE (widget)),
+                 g_type_name (G_OBJECT_TYPE (container)),
+                 g_type_name (G_OBJECT_TYPE (container)),
+                 g_type_name (G_OBJECT_TYPE (priv->child)));
+      return;
+    }
+
   if (priv->expanded)
     {
       gtk_container_add (GTK_CONTAINER (priv->box), widget);