list.data->signal_item_added.connect(sigc::mem_fun(this, &DataObserver::item_added));
list.data->signal_item_removed.connect(sigc::mem_fun(this, &DataObserver::item_removed));
list.data->signal_cleared.connect(sigc::mem_fun(this, &DataObserver::cleared));
list.data->signal_item_added.connect(sigc::mem_fun(this, &DataObserver::item_added));
list.data->signal_item_removed.connect(sigc::mem_fun(this, &DataObserver::item_removed));
list.data->signal_cleared.connect(sigc::mem_fun(this, &DataObserver::cleared));