public Hub(Func<HubState> restoreStateHandler, Action<HubState> saveStateHandler)
{
if (restoreStateHandler == null)
throw new ArgumentNullException ("restoreStateHandler");
if (saveStateHandler == null)
throw new ArgumentNullException ("saveStateHandler");
save_state_handler = saveStateHandler;
state = restoreStateHandler ();
}
void Save(HubState state)
{
using (var xw = XmlWriter.Create (store_file_name))
serializer.WriteObject (xw, state);
}