gtkcontainer: clarify requirements for implementations

Spent quite a few time investigating why the widgets were
not shown in my GtkContainer implementation.

https://bugzilla.gnome.org/show_bug.cgi?id=758087

diff --git a/gtk/gtkcontainer.c b/gtk/gtkcontainer.c
index 30a6d1ef79be87d96f0b07503577401a9561e5fd..9c4b81d70a3f04072b4eda83127b2b11e8c6a575 100644 (file)
--- a/gtk/gtkcontainer.c
+++ b/gtk/gtkcontainer.c
@@ -80,6 +80,16 @@
  * children in a horizontal row, and a #GtkGrid arranges the widgets it contains
  * in a two-dimensional grid.
  *
+ * For implementations of #GtkContainer the virtual method #GtkContainerClass.forall()
+ * is always required, since it's used for drawing and other internal operations
+ * on the children.
+ * If the #GtkContainer implementation expect to have non internal children
+ * it's needed to implement both #GtkContainerClass.add() and #GtkContainerClass.remove().
+ * If the GtkContainer implementation has internal children, they should be added
+ * with gtk_widget_set_parent() on init() and removed with gtk_widget_unparent()
+ * in the #GtkWidgetClass.destroy() implementation.
+ * See more about implementing custom widgets at https://wiki.gnome.org/HowDoI/CustomWidgets
+ *
  * # Height for width geometry management
  *
  * GTK+ uses a height-for-width (and width-for-height) geometry management system.