void ToggleCell_Toggled(object o, ToggledArgs args)
{
TreeIter iter;
if (filter.GetIterFromString(out iter, args.Path))
{
var t = (Task)filter.GetValue(iter, 0);
t.IsDone = !t.IsDone;
tasksList.SetValue(FindTask(t, tasksList), 1, t.IsDone); // NotImplementedException workaround
TaskManager.Instance.AddTask(t);
}
}