ArcGIS Pro 2.8 API Reference Guide
ReverseOrientation Method (MultipartBuilder<T>)
Example 

ArcGIS.Core.Geometry Namespace > MultipartBuilder<T> Class : ReverseOrientation Method
Changes the direction of the MultipartBuilder parts without changing the spatial position of the parts. The From Point and To Point of each Segment in each part of the MultipartBuilder are interchanged. This method must be called on the MCT. Use QueuedTask.Run.
Syntax
public void ReverseOrientation()
Public Sub ReverseOrientation() 
Exceptions
ExceptionDescription
This method or property must be called within the lambda passed to QueuedTask.Run.
Remarks
Caution should be taken in using ReverseOrientation on Polygons. Since ReverseOrientation changes the direction of each part within the Polygon, all Exterior Rings become Interior Rings and vice versa.

GeometryEngine Reverse Orientation

Example
// Builder constructors need to run on the MCT.
ArcGIS.Desktop.Framework.Threading.Tasks.QueuedTask.Run(() =>
{
  using (PolylineBuilder polylineBuilder = new PolylineBuilder(polyline))
  {
    polylineBuilder.ReverseOrientation();
    Polyline reversedPolyline = polylineBuilder.ToGeometry();
  }
});
Requirements

Target Platforms: Windows 10, Windows 8.1

See Also

Reference

MultipartBuilder<T> Class
MultipartBuilder<T> Members