getSelection
Gets the set containing all currently selected items in the model.
This function may be slow, so if you are only interested in single item, consider using method@Gtk.SelectionModel.is_selected or if you are only interested in a few, consider method@Gtk.SelectionModel.get_selection_in_range.
Return
a GtkBitset containing all the values currently selected in @model. If no items are selected, the bitset is empty. The bitset must not be modified.