public static Polyline FromJson( 
   string jsonString
)

{
  // MapPoint
  string inputString =
    "{\"x\":1,\"y\":2,\"spatialReference\":{\"wkid\":4326,\"latestWkid\":4326}}";
  Geometry geometryFromJson = GeometryEngine.Instance.ImportFromJson(
    JsonImportFlags.JsonImportDefaults, inputString);

  MapPoint importPoint = geometryFromJson as MapPoint;
  // importPoint = 1, 2
  // importPoint.SpatialReference.WKid = 4326

  // use the MapPointBuilderEx convenience method
  MapPoint importPoint2 = MapPointBuilderEx.FromJson(inputString);
  // importPoint2 = 1, 2
  // impointPoint2.SpatialReference.Wkid = 4326

  string outputString = GeometryEngine.Instance.ExportToJson(
    JsonExportFlags.JsonExportDefaults, importPoint);
  // outputString =
  //   "{\"x\":1,\"y\":2,\"spatialReference\":{\"wkid\":4326,\"latestWkid\":4326}}"

  string outputString2 = importPoint.ToJson();

  inputString =
    "{\"spatialReference\":{\"wkid\":4326},\"z\":3,\"m\":4,\"x\":1,\"y\":2}";
  importPoint = GeometryEngine.Instance.ImportFromJson(
    JsonImportFlags.JsonImportDefaults, inputString) as MapPoint;
  // importPoint.HasM = true
  // importPoint.HasZ = true
  // importPoint.X = 1
  // importPoint.Y = 2
  // importPoint.M = 4
  // importPoint.Z = 3

  importPoint2 = MapPointBuilderEx.FromJson(inputString);

  // export to json - skip spatial reference
  outputString = GeometryEngine.Instance.ExportToJson(
                JsonExportFlags.JsonExportSkipCRS, importPoint);
  // outputString = "{\"x\":1,\"y\":2,\"z\":3,\"m\":4}"

  // export from mappoint, skipping the sr - same as GeometryEngine.Instance.ExportToJson w JsonExportFlags.JsonExportSkipCRS
  outputString2 = importPoint.ToJson(true);

  //
  // Multipoint
  //
  List<Coordinate2D> coords = new List<Coordinate2D>()
{
  new Coordinate2D(100, 200),
  new Coordinate2D(201, 300),
  new Coordinate2D(301, 400),
  new Coordinate2D(401, 500)
};

  Multipoint multipointFromCoords = MultipointBuilderEx.CreateMultipoint(
    coords, SpatialReferences.WebMercator);

  inputString =
    "{\"points\":[[100,200],[201,300],[301,400],[401,500]],\"spatialReference\":{\"wkid\":3857}}";
  Multipoint importMultipoint =
    GeometryEngine.Instance.ImportFromJson(
           JsonImportFlags.JsonImportDefaults, inputString) as Multipoint;
  // importMultipoint.IsEqual(multipoint) = true

  ReadOnlyPointCollection pointsFromMultipoint = importMultipoint.Points;
  // points.Count = 4
  // points[0] = 100, 200
  // points[1] = 201, 300
  // points[2] = 301, 400
  // points[3] = 401, 500

  // use the MultipointbuilderEx convenience method
  Multipoint importMultipoint2 = MultipointBuilderEx.FromJson(inputString);
  // importMultipoint2.IsEqual(multipoint) = true

  // export to json
  outputString = GeometryEngine.Instance.ExportToJson(
                  JsonExportFlags.JsonExportDefaults, multipointFromCoords);
  // outputString = inputString

  // or use the multipoint itself
  outputString2 = multipointFromCoords.ToJson();

  //
  // Polyline
  //
  Polyline polylineFromCoords = PolylineBuilderEx.CreatePolyline(
                           coords, SpatialReferences.WebMercator);

  // export without the spatial reference
  outputString = GeometryEngine.Instance.ExportToJson(
                          JsonExportFlags.JsonExportSkipCRS, polylineFromCoords);
  // import
  geometry = GeometryEngine.Instance.ImportFromJson(
               JsonImportFlags.JsonImportDefaults, outputString);
  Polyline importPolyline = geometryFromJson as Polyline;
  // importPolyline.SpatialReference = null


  pointsFromMultipoint = importPolyline.Points;
  // points.Count = 4
  // points[0] = 100, 200
  // points[1] = 201, 300
  // points[2] = 301, 400
  // points[3] = 401, 500

  // use the polylineBuilderEx convenience method 
  Polyline importPolyline2 = PolylineBuilderEx.FromJson(outputString);
  // importPolyline2 = importPolyline

  outputString2 = importPolyline2.ToJson();
  // outputString2 = outputString

  //
  // Polygon
  //
  Polygon polygonFromCoords = PolygonBuilderEx.CreatePolygon(
                                coords, SpatialReferences.WebMercator);

  // export without the spatial reference
  outputString = GeometryEngine.Instance.ExportToJson(
                            JsonExportFlags.JsonExportSkipCRS, polygonFromCoords);
  // import
  geometryFromJson = GeometryEngine.Instance.ImportFromJson(
                       JsonImportFlags.JsonImportDefaults, outputString);

  Polygon importPolygon = geometry as Polygon;
  // importPolygon.SpatialReference = null
  pointsFromMultipoint = importPolygon.Points;
  // points.Count = 5

  // polygonBuilderEx convenience method
  Polygon importPolyon2 = PolygonBuilderEx.FromJson(outputString);
  // importPolygon2 = importPolygon

  // export from the polygon
  outputString2 = importPolyon2.ToJson(true);

  // Empty polygon
  polygon = PolygonBuilderEx.CreatePolygon(SpatialReferences.WebMercator);
  outputString = GeometryEngine.Instance.ExportToJson(
                                 JsonExportFlags.JsonExportDefaults, polygon);
  importPolygon = GeometryEngine.Instance.ImportFromJson(
                      JsonImportFlags.JsonImportDefaults, outputString) as Polygon;

  // importPolygon.IsEmpty = true
  // importPolygon.SpatialReference.Wkid = 3857
}