Created attachment 149411 [details] [review]
implementation

As it stands, GtkTreeModelFilter doesn't provide its visible and modify functions as vcalls you can implement in a subclass. If you want to provide a class with some filtering options, you have to set the function in init(), which makes it possible for someone to accidentally replace the filtering function, and break your subclass.

This patch exposes the visible() and modify() methods as vcalls in the class structure, allowing them to be implemented by a subclass. The subclass can then choose whether or not to chain-up the parent implementation (e.g. for additional custom filtering).

Here is an example from the upcoming Telepathy-Gtk, where the user can set the show_hidden property (more properties to come in the future) and then still add additional custom filtering if she wishes:

static gboolean
tp_gtk_roster_model_filter_visible (GtkTreeModelFilter *self,
                                    GtkTreeModel       *child_model,
                                    GtkTreeIter        *iter)
{
  TpGtkRosterModelFilterPrivate *priv = GET_PRIVATE (self);
  TpGtkRosterModelColumnType type;
  TpConnectionPresenceType state;
  gboolean v;
 
  gtk_tree_model_get (child_model, iter,
      TP_GTK_ROSTER_MODEL_CONTACT, &type,
      TP_GTK_ROSTER_MODEL_STATE, &state,
      -1);

  v = (priv->show_hidden || type == TP_GTK_ROSTER_MODEL_COLUMN_TYPE_GROUP ||
      (state != TP_CONNECTION_PRESENCE_TYPE_UNSET &&
       state != TP_CONNECTION_PRESENCE_TYPE_OFFLINE &&
       state != TP_CONNECTION_PRESENCE_TYPE_UNKNOWN &&
       state != TP_CONNECTION_PRESENCE_TYPE_ERROR));

  return v &&
    GTK_TREE_MODEL_FILTER_CLASS (tp_gtk_roster_model_filter_parent_class)->visible (self, child_model, iter);
}

http://git.collabora.co.uk/?p=user/danni/gtk%2B.git;a=commitdiff;h=850f2681cdf632d5afa616538d4403c2b9e40854