List<T>转IEnumerable<T>

  public static Polyline gettwoLine(double x1, double y1, double x2, double y2)
        {
            Coordinate2D p1 = new Coordinate2D(x1, y1);
            Coordinate2D p2 = new Coordinate2D(x2, y2);
            List<Coordinate2D> pList = new List<Coordinate2D>();
            pList.Add(p1);
            pList.Add(p2);

            IEnumerable<Coordinate2D> coordinates = pList.AsEnumerable<Coordinate2D>();
            //IEnumerable<Coordinate2D> coordinates =(p1,p2);

            var newPolyline = PolylineBuilder.CreatePolyline(coordinates);

            return newPolyline;
        }