Gtk+/Gnome Application Development - GtkVBox: A Windowless Container

Gtk+/Gnome Application Development
Prev	Home	Next

Child Arguments

GtkBox implements child arguments, which were briefly described in the section called Using Object Arguments in Your Own GtkObject Subclass in the chapter called The GTK+ Object and Type System. Child arguments represent a property of a pair of objects. In this case, the box-packing flags for each child can be read and written using the object argument system.

Here's how GtkBox registers its child arguments, in gtk_box_class_init():

  gtk_container_add_child_arg_type ("GtkBox::expand", GTK_TYPE_BOOL, GTK_ARG_READWRITE, CHILD_ARG_EXPAND);
  gtk_container_add_child_arg_type ("GtkBox::fill", GTK_TYPE_BOOL, GTK_ARG_READWRITE, CHILD_ARG_FILL);
  gtk_container_add_child_arg_type ("GtkBox::padding", GTK_TYPE_ULONG, GTK_ARG_READWRITE, CHILD_ARG_PADDING);
  gtk_container_add_child_arg_type ("GtkBox::pack_type", GTK_TYPE_PACK_TYPE, GTK_ARG_READWRITE, CHILD_ARG_PACK_TYPE);
  gtk_container_add_child_arg_type ("GtkBox::position", GTK_TYPE_LONG, GTK_ARG_READWRITE, CHILD_ARG_POSITION);

GtkBox then implements the get_child_arg and set_child_arg methods from GtkContainerClass. Here's gtk_box_get_child_arg(); the gtk_box_set_child_arg() is analagous.

static void
gtk_box_get_child_arg (GtkContainer   *container,
                       GtkWidget      *child,
                       GtkArg         *arg,
                       guint           arg_id)
{
  gboolean expand = 0;
  gboolean fill = 0;
  guint padding = 0;
  GtkPackType pack_type = 0;
  GList *list;

  if (arg_id != CHILD_ARG_POSITION)
    gtk_box_query_child_packing (GTK_BOX (container),
                                 child,
                                 &expand,
                                 &fill,
                                 &padding,
                                 &pack_type);
  
  switch (arg_id)
    {
    case CHILD_ARG_EXPAND:
      GTK_VALUE_BOOL (*arg) = expand;
      break;
    case CHILD_ARG_FILL:
      GTK_VALUE_BOOL (*arg) = fill;
      break;
    case CHILD_ARG_PADDING:
      GTK_VALUE_ULONG (*arg) = padding;
      break;
    case CHILD_ARG_PACK_TYPE:
      GTK_VALUE_ENUM (*arg) = pack_type;
      break;
    case CHILD_ARG_POSITION:
      GTK_VALUE_LONG (*arg) = 0;
      for (list = GTK_BOX (container)->children; list; list = list->next)
        {
          GtkBoxChild *child_entry;

          child_entry = list->data;
          if (child_entry->widget == child)
            break;
          GTK_VALUE_LONG (*arg)++;
        }
      if (!list)
        GTK_VALUE_LONG (*arg) = -1;
      break;
    default:
      arg->type = GTK_TYPE_INVALID;
      break;
    }
}