my codes
        PointShape startPoint = new PointShape(57.6538, -20.1305);
        PointShape endPoint = new PointShape(57.4283, -20.4254);
        List<PointShape> viaPoints = new List<PointShape>();
        for (int i = 0; i < lPoints.Count; i++)
        {
            Double lon = lPoints[i].lon;
            Double lat = lPoints[i].lat;
            PointShape myPoint = new PointShape(lon, lat);
            if (i == 0)
                startPoint = myPoint;
            else if (i == lPoints.Count - 1)
                endPoint = myPoint;
            else
                viaPoints.Add(myPoint);
        }
        // route shape
        RoutingEngine engine = new RoutingEngine(routeSource, shapeFileSource);
        engine.SearchRadiusInMeters = searchRadiusInMeters;
        RoutingResult rr = engine.GetRoute(startPoint, endPoint, viaPoints);
        return rr;
i tried RoutingResult rr = engine.GetRoute(startPoint, viaPoints); but that does not return any ShapeLines